o ye s » . a " sf » A ’ ‘ a a : 3 . 2 Le sbed adimce aloe oe . erp eat ass ; eraser ete eat A free hud As _ ; . » a 4 ¢ 4 ‘| y ‘ i nomen - Lets ee pee eee P 2 re a = e S 3.4 ‘ 3 = - a 4 ~ kee eg A 4 . se at hear Ss <4 i tne ae perk ER a ote oa A ee eet ae Sarena Poy a io rae a thet ore hms pee ae Sree p. Ase’ # ie ihe ALBERT R. MANN LIBRARY NEw York STATE COLLEGES OF AGRICULTURE AND HomE ECONOMICS AT CORNELL UNIVERSITY DATE DUE GAYLORD PRINTED INU.S.A. ! oon University Library aL 45.K' ~ (mil natural hist mn NATURAL HISTORY OF INVERTEBRATES. SAMUEL F. CLARKE, Ph.D. D. 8S. KELLICOTT, Ph.D. J. WALTER FEWKES, Ph.D. J. S. KINGSLEY. ROMYN HITCHCOCK. W. N. LOCKINGTON. ALPHEUS HYATT. CHARLES S. MINOT, D.Sc. ALPHEUS 8. PACKARD, Ph.D. Cucumaria hyndemanni, sea cucumber. THE STANDARD NATURAL HISTORY. EDITED BY JOHN STERLING KINGSLEY. VoL. I. LOWER INVERTEBRATES. Mustrated BY FIVE HUNDRED AND ONE WOOD-CUTS AND TWENTY-TWO FULL-PAGE PLATES. Boston: Ss. E. CASSINO AND COMPANY. 1885. ee) Fut il 7g Copyright by S. E. Cassino AND COMPANY, 1884. = VON IVERSITY Hf “fy PRESS. ff Ss Cc. J. PETERS AND SON, STEREOTYPERS AND ELECTROTYPERS, 145 Hiew STREET. CONTENTS. PAGE INTRODUCTION Z 3 "i ae : ‘i ‘ a ‘ é ‘ ‘ ‘ * - i Brancu I.—PrRorozoa . ‘i : ‘ - 5 é . ‘ i é : 3 . 1 Crass I. —Monera . 7 3 7 7 : ‘i - ‘ 5 : ‘ . a 2 Cuass II. —RuIzopopa 3 ‘ - ‘ ‘ ‘ 3 . ‘ ‘i ‘ s : 4 Cxiass III.—GREGARINIDA . é - i 4 . ‘ ‘ 7 é ‘ : . 28 Ciass IV. — INFuUSORIA : 4 ‘ , ‘ : : 3 ‘ ‘ a , si 26 Brancu Il. — PoRiFERATA . . : 3 ‘ a , ‘ ‘ i ‘ 7 3 . 49 Ciass I. —CALCISPONGIZ . 3 ‘5 ‘ ‘ és . ‘ ‘ : 3 i Fi 61 Cuass II. — CARNEOSPONGIZ . 5 : 3 . F , ‘ : 2 : ‘ . 63 Brancw IL]. — C@LENTERATA . a 3 ‘ ‘ - ‘ 3 ‘ ‘ 3 ‘i 2 Ciass I.—Hyprozoa . : - . 5 P 5 F - 3 ‘i : 5 . 72 OrDER I.—HypDROIDEA . , ‘i é ‘ 3 3 ‘: * 3 3 * 13 ORDER II. — DiscopHora 5 5 : . : é ‘i ; ‘ : . . 89 Cuass II. —SIPHONOPHORA . : : ‘ . ‘ ‘ F 3 ‘ 7 - 97 OrDER I.—PHYSOPHORZE . 7 < ‘ 7 : i ‘ ‘ ‘ fi » 98 ORDER II. — PNEUMATOPHORZ . i . og ab : : . ‘ : 104 ORDER ITI.— DipHy#z . ‘ 5 r ‘ : “ 4 - - a F - 105 OrnpeER IV.—Discome#z . . . 2... ee 107 Cuass III. — CTENOPHORA : ‘ : if ‘ 3 : - : : - ‘ - 108 Crass IV. — ACTINOZOA é ‘ ‘ : S S 5 3 ‘ 7 ‘ $ : 112 OrveER I. — ZOANFHARIA t n . ‘ i ‘ A : ‘ ‘ % - 116 ORDER IT. — HALCYONOIDA m < ‘ g : ‘ 3 ‘ ‘i : 2 121 BRANCH IV. — ECHINODERMATA. : : 5 3 - 7 A : 2 - ‘ - 135 Cuass I.—CRINOIDEA . ‘ : 2 : é 5 F ; 2 . el : : 139 ORDER J. — BLASTOIDEA ‘ ‘ ‘ 7 3 é s 2 F 4 “ - 1389 OrpDER II. — CysTIDEA 3 ‘ r ‘ ‘ 3 ‘i ‘ 2 ‘ : “ 139 ORDER III. — BRACHIATA . : : ‘ : ‘ is : j . é . 140 Cuass II. —STELLERIDA . F é ‘ ‘ : ‘ ‘ 5 3 " ‘ 147 OrpER I.—OPHIUROIDEA . ‘ : 3 ‘ ° i ‘ : : ; . 147 ORDER II. — ASTEROIDEA . : ‘i ‘ : : . : P s si ‘ 152 Crass III. — EcHINOIDEA : i ‘ ‘i 3 : A - . : ‘ a . 161 ORDER I. — DESMOSTICHA . f ‘ ‘ : ‘ . : “ 3 : ‘ 164 OrpER II. — CLYPEASTRIDZ . , ‘ 2 4 ‘ e i ‘ . ‘ . 170 OrDER III. —PETALOSTICHA . - 3 ‘ : : é ‘ 5 . i 172 CLass IV. — HoLoTHUROIDEA. i ‘ 3 é ‘ ‘ i 5 7 : A . 176 OrpDER I.—ELASIPODA . é 7 : 5 : . 5 ; 5 3 j 179 ORDER II. — APopa ‘ , ‘ 7 . ; 2 3 é < : 4 . 179 ORDER III. — PEDATA - z é ; ; ‘ 3 . : . - 180 ORDER IV. — DIPLOSTOMIDEA * "i . : 3 é : ; . : . 183 CONTENTS. BRANCH V. — VERMES Cuiass J. — PLATHELMINTHEA . Sus-Cuass I. — TURBELLARIA. Sus-Cuass II. — TREMATODA Sup-Cuass III. —CrEstopa Cuass Il. — RoTiIreRa - Cass III. — GAstrorrRicua Z ‘ . ‘ ‘ ‘ 3 < ‘ 7 Cuass IV. —NEMATODA . ‘ Cuiass V. — ACANTHOCEPHALI i z - . - ¥ 3 5 Cuass VI.—CHATOGNATHI . ‘ : : Z x 3 é ‘ Cuass VII.—NEMERTEA . ‘i ‘ i . . - 5 - . 7 ‘ Cuass VII. — Gevnyrea : _ . . J ‘ 7 . . A Cuass IX.— ANNELIDA j ‘ ‘ ; 5 ‘i fs . Sus-Cuass I. — ARCHIANNELIDA c ; ‘ : 3 i 3 Sus-C.Lass II.—CH2&ToPODA . Sus-Ciass III. — ENTEROPNEUSTI Sus-CuLass IV. — DiscopHor! . Brancnu VI. — MOLLUSCOIDEA . A 3 A . . Ciass I.—Poutyzoa . é ; - ‘ 5 3 : 3 ‘ ° ‘ . Sus-Cuass I, — ENTOPROCTA . ‘ : ‘ aj 3 a i . Sus-Cuass IT. — EcroPprocta . j < ‘ ‘ Sus-CLass III. —PopDOSTOMATA . . ‘ 3 Fi a ‘i é 3 CLass II.— BRACHIOPODA . : J A 3 i 3 ‘ 3 3 F Brancu VIL—MonuuscA. . . «2. 2. we ee Cuass IL.—ACEPHALA. . 6 0. eee Cuass II]. —CEPHALOPHORA . ‘ 4 3 : ‘ 5 3 . ‘ ; SuB-CLass I. —ScapPHopopDa . : ‘ 3 x ‘ - - - > é Sus-Cuiass II. —GASTEROPODA . , ‘ ‘ ; 3 fi Fi i SUPER-ORDER I. —ISOPLEURA . - 3 5 5 . ‘ ; i OrDER I.—CHATODERME . , ‘ A ‘i ‘ i ij . 5 OrpER II.— NEOMENOIDEA é ‘ ‘ F - ‘ r ‘ 5 ORDER III. — POLYPLACOPHORA . SurER-ORDER II. — ANISOPLEURA ‘ 2 7 ‘ é ‘ ‘ r ORDER I. — OPISTHOBRANCHIATA . ORDER IJ. —PULMONATA . i : ‘ : 7 : ‘ : : ORDER III. — ZYGOBRANCHIA ORDER IV. —SCUTIBRANCHIA . F 5 ‘ js , : ORDER V. — CTENOBRANCHIA ‘ ¥ ; , . OrpER VI. — HETEROPODA ; : i . . 7 A : ‘ Susp-C.ass III.—PTEROPODA . : ‘ ‘ ‘ 3 ‘ OrvDER I. — THECOSOMATA. 2 3 5 - ‘ : : : : OrpDER II. —GyMNOSOMATA . r ‘ : . 3 : . r : Cuass III. —CEPHALOPODA 3 é ° 4 ‘ : SuB-Cuass I. — TETRABRANCHIATA Sup-Cuass II.— DIsRANCHIATA . ; a. OR ; 5 ‘ j ‘ ; OrvER I. — OcTorpopa OrvrEr II.— DEcCACERA . . é . és . 3 185 187 188 191 198 202 206 207 213 213 215 217 218 219 219 231 232 236 236 239 240 244 244 248 252 287 201 292 292 292 292 298 204 295 808 319 822 824 358 356 357 359 360 367 369 369 872 LIST OF PLATES. PAGE Sea CUCUMBER . ‘ ; , ‘ - : . * i é . 7 . Frontispiece POLYSTOMELLA . . Fy ‘ ‘ ‘i : " . . ; A 3 16 SPONGES “oe é é : 7 ‘ P 2 i 7 ‘ . F ‘ : . 56 DALMATIAN SPONGE FISHERY . é ‘ ‘i . . : : : ‘i 64 GORGONIA VERRUCOSA . 7 . - F . i : 7 = ‘ é . . 72 TUBULARIAN HypRoIp . ‘ ‘ : . 4 : s . z : 5 r 5 80 Hyproip JELLY-FISHES : . 3 - - ‘ : ‘ ‘ é , : . 82 HyDROIDs . . - ‘ . ; ‘ 3 . ‘ ‘ : 3 ‘ “ ‘ ‘ 86 CORALLINE JELLY-FISH ‘ 3 : 1 : . ‘ ‘i é é é 5 3 . 90 PLEUROBRACHIA AND BOUGAINVILLEA ‘ ‘i 5 3 : x ‘ 3 ° 110 EUROPEAN SEA-ANEMONES. 3 ‘ ! 3 F 3 ‘ - s ‘ : < . 114 RED CoRAL - . ‘ a ‘ ‘ ; 5 4 i ‘ 2 m P * 122 Cork POLYP . ; : 3 5 : ; s ‘ ‘ a . ‘ 3 a ‘ - 128 Livine CRINOIDS . si : 3 3 7 ‘ ‘ 5 a ‘ * e ‘ 146 STar-FisH, HOLOTHURIAN, AND WORMS . 4 z - ; ‘ 5 3 ‘ : - 160 MARINE WORMS ; . . 5 4 ‘ ‘ ‘ ‘ 5 , 4 F : ‘ 228 BIVALVE MOLLUSCS . 7 ‘ 5 7 3 3 ‘ ‘ ‘ ‘ F : ‘ - 276 AMERICAN LAND SHELLS . é 5 ‘ . ‘ 3 i : , “ - - 314 AMERICAN PoND SNAILS. ‘ ‘i j ‘ : ‘ ‘ é 3 ‘ : ‘ . 3840 PTEROTRACHEA . : 2 é A ‘ ‘ é ‘ : ‘ 3 r a 7 . 356 Musk POULPE 2 5 3 7 ‘ ‘ 2 pi ‘i r ‘ 3 , . ‘ . 3872 CUTTLE-FIisH . ‘i a 3 é ‘ . ‘ és i . ‘i : A 374. THE ANIMAL KINGDOM. INTRODUCTION. Tux term Natural History has at different times and by different authors been used in a variety of senses. At the present time it is perhaps more commonly used in con- tradistinction to natural philosophy ; it is generally applied to the study of natural ob- jects, both mineral or inorganic, and to plants and animals, or organic bodies, At first it was applied to the study of all natural objects, whether the minerals, rocks, and living beings observed upon our own planet, or heavenly bodies in general. The study of external nature, and the phenomena or laws governing the movements of natural bodies, was formerly opposed to metaphysics, history, literature, ete. After a while astronomy and chemistry were eliminated from natural history; then natural philosophy, or what is now called physics, was farther separated from chemistry, so that a chemist studies the constitution or atomic nature of bodies, both inorganic and organic; how they combine, and how compound bodies may be analyzed or separated into their simple constituents ; the natural philosopher, or physicist, studies the forces of nature, the mechanical movements of inorganic bodies, and their phenomena, such as light, heat, and electricity, while the naturalist studies minerals, rocks, plants, and animals. But natural science, as distinguished from physical science, has made such progress, the work has been so sub-divided or differentiated, that even the term naturalist has become a vague, indefinite one. We must now know whether our naturalist is a mineralogist, a geologist, a botanist, or a zoologist; and the latter may be an entomologist, or ichthyologist, or ornithologist, according as he devotes himself exclusively to insects, fishes, or birds. The term natural history is popularly, at least by many, confined to botany and zoology, often, however, to zoology alone ; and such is the convenient though inexact-title of the present work. Man is an animal as well as a mental and spiritual being. His material body is dom- inated by his mind and soul, but as zoologists we study him simply as an animal. The natural history of man is his physical history ; it concerns his bodily structure and de- velopment, the work of his hands and the language he speaks, as well as the races into which his species is divided. Anthropology is a convenient and comprehensive term now generally used for the natural history of man. The anthropologist, making a specialty of the natural history of man, studies not only his bodily structure, especially his skull or cranium and the other bones of the skeleton, comparing those of different races both living and extinct, but the works of human art; also human languages, both those now spoken and those which have become extinct. Moreover the anthropologist goes out of the realm of zoology into those of mental phenomena or psychology, and of sociology, and studies man as 2 spirit, his notions of the future life, his myths, traditions; he also studies his origin, history, and social laws and government. i il THE ANIMAL KINGDOM. We have seen that the term natural history, as applied to plants and animals, is in- exact, having been used in different senses; a more exact and suitable one is Biology, which is the science which relates to living beings. It is derived from the Greek Bios, life, and Adyos, discourse. It is divided into Botany, which relates to plants, and Zoology (cor, animal; Adyos, discourse), the science treating of animals. The science of zoology may be subdivided thus: MoRPHOLOGY, or gross Anatomy, and the anatomy of the tissues (HisToLoGy), based on embryology. Puysio_oey and PsycHoLoey. ZOOLOGY. } REPRopucTION and EMBRYOLOGY. SYSTEMATIC ZOOLOGY, or Classification. PALZONTOLOGY, the study of fossil animals. Z00-GEOGRAPHY, or the geographical distribution of animals, MORPHOLOGY. Inorganic AND OrGanic Bopiszs. The differences between the inorganic or mineral bodies, and organic or living bodies, are not always appreciable to the untrained eye and mind. Mineral bodies, such as water, and solid minerals such as quartz, salt, or lime, may assume definite crystalline shapes, and such shapes may grow, 7. e. increase in size, by the addition, on the outside, of particles of the same substance. Minerals may exist in three different states, gas or vapor, fluid, or solid. The air, carbonic acid gas, and water are min- erals, as much so as lime or salt. Rocks are made up of minerals, and thus the earth, the air, and water are of mineral origin. Minerals may assume plant-like shapes, as seen in the beautiful forms and delicate leaf-like tracery of the frost on our windows. The drops of sea-water dashed by the waves upon one’s coat-sleeve may be seen under a glass to evaporate and the solid particles left to arrange themselves in beautiful but definite crystalline forms. By watching the evaporation of salt water under the micro- scope, the crystals may be seen actually to grow, ¢. e. to build themselves up, to extend and enlarge in size. “If,” as Huxley states, “a crystal of common salt is hung by a thread in a saturated solution of salt, which is exposed to the air so as to allow the water to evaporate slowly, the molecules of the salt which is left behind and can no ‘longer be held in solution, deposit themselves on the crystal in regular order and in- crease its size without changing inform. And, in this way, the small crystal may grow to a great size.” Thus growth in minerals consists in the addition of particle after particle of solid matter to the outside of the growing body. Now, how do living bodies essentially differ from those not living? In the first place, plants and animals are built up of protoplasm. Protoplasm consists of mineral matter, to be sure, but so combined as to form a substance not found in minerals. Moreover, a plant or animal has life; the plant grows, and, if it is a vine, is capable of some degree of motion, it twines about some post or tree as a support; the living bird flies, and the living dog runs; after a time the plant or the bird dies, it is then dead. Minerals do not die. Besides, when the plant or animal grows, it increases in size, not like minerals, by additions from without, but by manufacturing protoplasm and other organic substances, such as starch and fat, within its body. Thus organisms or living beings grow by additions from within, these additions being produced by the living being itself. After a while this process stops and it becomes dead. As Professor Hux- INTRODUCTION. iil ley tells us: “In the spring, a wheat-field is covered with small green plants. These grow taller and taller until they attain many times the size which they had when they first appeared ; and they produce the heads of flowers which eventually change into ears of corn. “In so far as this is a process of growth, accompanied by the assumption of a defi- nite form, it might be compared with the growth of a crystal of salt in brine; but, on closer exaiination, it turns out to be something very different. For the crystal of salt grows by taking to itself the salt contained in the brine, which is added to its exterior; whereas the plant grows by addition to its interior; and there is not a trace of the characteristic compounds of the plant’s body, albumen, gluten, starch, or cellulose, or fat, in the soil, or in the water, or in the air. “Yet the plant creates nothing, and therefore the matter of the proteids and amy- loids and fats which it contains must be supplied to it, and simply manufactured, or combined in new fashions, in the body. of the plant. “It is easy to see, in a general way, what the raw materials are which the plant works up, for the plant gets nothing but the materials supplied to it by the atmosphere and by the soil. The atmosphere contains oxygen and nitrogen, a little carbonic acid gas, a minute quantity of ammoniacal salts, and a variable proportion of water. The soil contains clay and sand (silica), lime, iron, potash, phosphorus, sulphur, ammoniacal salts, and other matters which are of no importance. Thus, between them, the soil and the atmosphere contain all the elementary bodies which we find in the plant; but the plant has to separate them and join them together afresh. “ Moreover the new matter by the addition of which the plant grows is not applied to its outer surface, but is manufactured in its interior; and the new molecules are diffused among the old ones.” Living beings also reproduce their kind. The corn bears seed, the hen lays eggs. Minerals cannot reproduce, so that we see that organic beings differ from minerals in three essential characteristics: they contain and are built up from protoplasm; they grow from within, and they reproduce by seeds, germs or eggs. As Huxley again says: “Thus there is a very broad distinction between mineral matter and living matter. The elements of living matter are: identical with those of mineral bodies; and the fundamental laws of matter and motion apply as much to living matter as to mineral matter; but every living body is, as it were, a com- plicated piece of mechanism, which ‘goes’ or lives, only under certain conditions. The germ contained in the fowl’s egg requires nothing but a supply of warmth within certain narrow limits of temperature, to build the molecules of the egg into the body of the chick. And the process of development of the egg, like that of the seed, is neither more or less mysterious than that in virtue of which the molecules of water, when it is cooled down to the freezing point, build themselves up into regular crystals.” Tue DIFFERENCES BETWEEN Piants AND ANIMALS. We now come to the differences between plants and animals; and here the dis- tinctions are more or less arbitrary. As we have remarked elsewhere, — “Tt is difficult to define what an animal is as distinguished from a plant, when we consider the simplest forms of either kingdom, for it is impossible to draw hard and fast lines in nature. In defining the limits between the animal and vegetable king- doms, our ordinary conception of what a plant or animal is will be of little use in dealing with the lowest forms of either kingdom. a comparatively late stage of development. This is < carried to its furthest extent in some of the fishes. All of these modifications of the type of segmentation are variously combined, so that great differences result, and as in the eggs of the same class, or occasionally even of the same genus, the distribution of the food-yolk will vary, it will readily be seen that the segmentation is but a very poor guide to the relationships of forms. In the insects the segmentation is very greatly modified, but as yet our knowledge is so slight as not to warrant any — FI. ee broad generalizations on the earlier stages of the group. Correlated with the variations in the segmentation are certain modifications in the gastrulation and the production of the epiblast and hypoblast. Let us return to the normal gastrula for a moment, and trace its progress just a little farther, naming some of the points omitted above. The invagination is carried to such an extent that the segmentation cavity is nearly obliterated, and at the same time the edges of the in- folded ball are brought closer together, so that a comparatively narrow opening is the INTRODUCTION. = result, known as the blastopore. This blastopore in most forms completely closes ; but to this we will return again. The hollow, which we have mentioned above as form- ing primarily the digestive cavity, is known as the archenteron or primitive stomach, and the hypoblastic cells which form its boundary are almost invariably larger than those of the epiblast. This is true of all gastrulas, even those where the segmentation is regular, and the reason is not difficult to find. The external cells have to embrace a greater superficial extent than the internal ones, and hence the layer becomes thinner and the resulting cells smaller. In other cases the segmentation is irregular and then a greater inequality occurs, until in some forms the hypoblast is invaginated as a few cells, or even a single cell, and the archenteron does not appear until alater date, when it is hollowed out of the hypoblastic cells. A greatly different mode of forming the gastrula is by what is known as delamination. A general idea of the process may be obtained by saying that the inner ends of the cells of the blastula (Fig. II., G) are segmented off to form the hypoblast. In the gastrula we have two of the so-called germinal layers, the epiblast and the hypoblast; in all animals except some of the ceelenterates and the Dicyemids, a third layer, the mesoblast or mesoderm, occurs, hence these are known as triploblastic animals, in contradistinction to those with only hypoblast and epiblast, which are called diplo- blastic. We will not enter into a discussion of the many different ways in which the mesoblast arises, but will merely indicate what is apparently the typical method, which in reality exists unmodified in but very few animals. From the hypoblast, pouches bud off on either side, as shown on the left of our. figure. These pouches eventually become separated from the archenteron, as shown on the right side Fic. V.—Diagram illustrating the formation of the germ layers of the same figure, and the walls of these pouches are the —_ (but little modified from that occurring in Peripatus); on the mesoblast. Now we are ready for the names of these parts _ right an earlier, on the left a later stage; b, blastopore; c, and an enumeration of the organs into which they develop. —ceelom; ‘d, mesoblastic pouch; After the formation of the mesoblast and the separation of See. hy ee inte a portion of the archenteron, the hypoblastic cavity is a uavie, ture; s, segmenta- known as the mesenteron, from the fact that its lining cells form the epithelium of the middle portion of the digestive tract. From other pouches and outgrowths of the mesenteron, formed at a later date, other organs arise. Among these we may mention the liver, the lungs of vertebrates, the endostyle of tunicates, the thyroid and thymus glands, pancreas, spleen, and the notochord. The epiblast, as we have seen, gives rise to the outer layer of the skin. This is not the whole of the list of its derivatives, for we must here include the nervous sys- tem and the organs of sense, dermal glands, teeth, membrane-bones, etc. As we have said, the blastopore almost always becomes completely closed, but in some forms it remains open, forming the mouth or the vent, and in Peripatus it closes in the middle, leaving both oral and anal openings at its extremities. In these forms where it becomes completely closed, the mesenteron is entirely separated from the external world, and communication has to be again opened with the exterior. This is accom- plished by inpushings of the epiblast at the extremities of the body. These ingrowths finally meet and unite with the hypoblast, and thus form the complete alimentary tract. From this method of formation of the anterior and posterior parts of the digestive canal, it follows that certain internal organs, as the esophagus and intes- xii THE ANIMAL KINGDOM. tine, the stomach of the lobster, and the gizzard of the cricket, the malpigian tubes of insects, etc., are really to be classed among the derivatives of the epiblast. The mesoblast, after separating from the hypoblast, grows around between the other two layers. It either contains a cavity, originally a-part of the archenteron, or such a cavity soon appears. This is the body cavity or celom, the pleuro-peritoneal cavity of vertebrates. The outer wall of the celom unites with the epiblast, the inner with the hypoblast, and the segmentation cavity is obliterated. From the meso- blast arise most of the structures and organs not already enumerated. The list in- cludes the bones of vertebrates, the skeleton of echinoderms, spicules of sponges, mus- cles, connective tissue, blood, and excretory and reproductive organs. From an embryological standpoint, as we have just seen, we can arrive at a classi- fication of tissues; but if we turn to structure and function, the result is a different association, which, for all except the pure morphologist, is far more satisfactory. The following classification of the tissues is taken, with modifications, from K$lliker: — 1. Epithelial tissues (epidermal and glandular). 2. Connective tissues (mucous, cartilage, elastic, areolar, and osseous tissues, and dentine). 8. Muscular tissues (smooth and striated). 4. Nerve tissue (nerve-cells and fibres). The epithelial tissues consist of cells placed side by side, forming a layer. All the other tissues arise from one having the cells characteristic of epithelium, as the germ- layers are formed of it. As Kélliker reiterates in 1884, “In all multicellular organ- isms all the elements and tissues arise directly from the fertilized ege-cell and the first embryonic nucleus. (1) The tissues first differentiated have the characters of epithe- lial tissues, and form the ectoblast and endoblast. (2) All the other tissues arise from these two cell-layers; they are either directly derived from them, or arise by the intermediation of a median layer (mesoblast) which, when developed, takes an important part in forming the tissues. (8) When the whole of the animal series is considered, each of the germinal layers is found to be, in certain creatures, capable of giving rise to at least three, and perhaps to all tissues; the germinal layers cannot, therefore, be regarded as histologically primitive organs.” Epithelial cells form the skin or epidermis of animals, and also the lining of the digestive canal. The cells of the latter may, as in sponges, bear a general resemblance to a flagellate infusorian, as Codostga, or they may each bear many hair-like processes ealled cilia, which by their constant motion maintain currents of the fluids passing over the surface of the epithelium. The cilia lining the inside of the windpipe serve to sweep any fluid formed there towards the throat, where it can be coughed up and expectorated. Connective tissue and its varieties, and gristle or cartilage, bone, etc., arise from the mesoblast and support the parts of the body. All the supporting tissues are used in the body for mechanical purposes: the bones and cartilages form the hard framework by which softer tissues are supported and protected ; and the connective tissues, with the various bones and cartilages, form investing membranes around different organs, and in the form of fine network penetrate thelr substance and support their constit- uent cells. Connective tissue is formed by isolated rounded or elongated cells with wide spaces between them filled with a gelatinous fluid or protoplasm, and occurs between muscles, etc. Gelatinous tissue is a variety of connective tissue found in the umbrella INTRODUCTION. xiii of jelly fishes. Fibrous and elastic tissue are also varieties of connective tissue. Cartilaginous tissue is characterized by cells situated in a still firmer intercellular sub- stance; and when the intercellular substance becomes combined with salts of lime, forming bone, we have bony tissue. The blood-corpuscles originate from the mesoderm as independent cells floating in the circulating fluid, the blood cells being formed contemporaneously with the walls of the vessels enclosing the blood. In the invertebrates the blood-cells are either strikingly like the Amcbda in appearance, or are oval, but still capable of changing their form. Thus blood-corpuscles arise like other tissues, except that they become free. Muscular tissue is also composed of cells, which are at first nucleated and after- ward lose their nuclei. From being at first oval, the cells finally become elongated and unite together to form the fibrille; these unite with bundles forming muscular fibres, which in the vertebrates unite to form muscles. Muscular fibrille may be sim- ple or striated. The contractility of muscles is due to the contractility of the proto- plasm originating in the cells forming the fibrille. Nervous tissue is made up of nerve-cells and fibres proceeding from them; the former constituting the centres of nervous force, and usually massed together, forming a ganglion or nerve-centre from which nerve-fibres pass to the periphery and extremi- ties of the body, and serve as conductors of nerve-force. — (Packard’s Zoology.) ORGANS. Animals are, with plants, called organisms, because they have organs. An organ is any part of the body specially developed to perform a special kind of work. Thus the wings are organs of flight, the heart is the organ of circulation, the leg an organ of locomotion. The tissues we have enumerated are combined to form organs. The simplest kind of an organ is perhaps the nucleus of the Amaba. There are creatures lower than the Amba which have no organs. These are the Monera, in which no nucleus or any other specialized part of the body has as yet been found. If we rise in the scale of animal life to the monad, we find that it has an external appendage or organ like a whip-lash. In the Infusoria the body is covered with cilia, which are the only organs of locomotion in these animaleules. In the Hydra, the only external organs are the tentacles, which are situated around the head, and seem to feel for and to seize its prey. In the higher worms we have oar-like organs of locomotion, arranged in pairs on each side of the body; also gills, or external breathing organs. Molluscs have a creeping organ, the under side of the body; they also have gills and other external parts or organs. In the crustaceans and insects the number and variety of form of external organs, especially the legs, gills, feelers, and mouth-parts, are remark- able, and they are highly specialized. In the vertebrates, beginning with fishes and ending with man, we have external organs of sight, hearing, and locomotion, such as fins, hands, and legs. Of the internal organs of the body, the most important is the digestive cavity, which is at first in the gastrula or early embryo of all many-celled animals, and in the Hydra and other polyps simply a hollow in the body. As we ascend in the animal series we can trace its gradual specialization, beginning with the lower worms, and as- cending to the annelids, also in the sea-urchin and starfish. In the molluscs, Crustacea, and insects, as well as vertebrates, the alimentary canal is divided, during growth, into distinct portions (2. ¢., the throat, stomach, and intestine), each with separate functions xiv THE ANIMAL KINGDOM. or uses. Early in life other organs arise as outgrowths from the digestive tract of the embryo. These are the lungs, the liver, pancreas, spleen, etc. There are also organs of support; such are the skeletons of animals, whether exter- nal, as in the sea-urchin, starfish, lobster, or insect; or internal, as in a fish, bird, or man. A true bony skeleton only exists in the vertebrates, or back-boned animals. The illustrious naturalist, Cuvier, established the principle of the correlation of organs, showing that every organ must have close relations with the rest, and be more or less dependent on the others. Each organ has its particular value in the animal economy. There is a close relation between the forms of the hard and soft parts of the body, together with the functions they perform, and the habits of the animal. For example, in a cat, sharp teeth for eating flesh, sharp curved claws for seizing smaller animals, and great muscular activity — all coexist with a stomach fitted for the digestion of animal rather than vegetable food. So in the ox, broad grinding teeth for chewing grass; cloven, wide-spreading hoofs, that give a broad support in soft ground, and a four-chambered stomach, are correlated with the habits and instincts of aruminant. From the shape of a single tooth of an ox, deer, or a dog or cat, one can determine not only its order, but its family or genus. Hence this prime law of com- parative anatomy led to the establishment by Cuvier of the fundamental principles of the science of paleontology, by which the comparative anatomist can with some degree of confidence restore from isolated teeth or bones the probable form of the original pos- sessor. Of course, the more perfect the skeleton a . more perfect the remains of the crust of insects or the shells of extinct molluscs, the more perfect will be our knowledge, and the less room will there be for error in restoring extinct animals. New organs often arise by changes in the form and uses of simpler, older ones, and the new organs may be so much changed by the gradual modification of its func- tions as to assume new uses. “ This fact,” says Gegenbaur,in the introduction to his Elements of Comparative Anatomy, “is of considerable importance, for it helps to explain the appearance of new organs, and obviates the difficulty raised by the doc- trine of evolution, viz., that anew organ cannot at once appear with its function completely developed; that it therefore cannot serve the organism in its first stages whilst it is gradually appearing; and that consequently the cause for its development can never come into operation. Every organ for which this objection has the appear- ance‘of justice can be shown to have made its first appearance with a significance dif- fering from its later function. Thus, for example, the lungs of the Vertebrata did not arise simply as a respiratory organ, but had a predecessor among fishes breathing by gills, in the swim-bladder, which at first had no relation to respiration. Even where the lungs first assume the functions of a respiratory organ (Dipnoi, and many Am- phibia) they are not the sole organ of the kind, but share this function with the gills. The organ is therefore here caught, as it were, in the stage of conversion into a respi- ratory organ, and connects the exclusively respiratory lungs with the swim-bladder, which arose as an outgrowth of the enteric tube and was adapted to a hydrostatic function.” : Organs may also become modified by disuse until they lose their distinctive form and become rudimentary. Striking examples are seen in the parasitic Crustacea and insects. As a result of the modification of organs by use and disuse, organs which are morphologically the same become very different in function, and also in their general appearance; so that we may classify organs differently either by their morphology or physiological uses. INTRODUCTION. xv We speak of highly-developed organs, and those which are aborted, atrophied, or rudimentary. Highly-developed organs are also highly specialized or differentiated ; such organs are complicated, owing to the distinct uses or divisions of labor accorded to each part. Thus, the eyes of worms are very simple and lowly developed com- pared with the human eye; a fish’s fin is, in part at least, morphologically the same as the fore-leg of a cat, or the arm of a monkey or of man, but in the human arm different uses are assigned to different portions of the limb; it is highly developed, specialized, or differentiated, to use terms nearly synonymous. On the other hand, so exquisitely wrought an organ as a fish’s eye may by disuse become nearly atrophied, as in the blind fish of Mammoth Cave, which lives in perpet- ual darkness. And not only the eye, but the optic lobes and optic nerves may, as in the case of a small crustacean (Cecidotcea stygia), also living in Mammoth Cave, be entirely aborted. Among reptiles are some extraordinary cases of modification by degeneration and atrophy. The lizard-like creature, Seps, has remarkably small limbs, and in Bipes there is only a pair of stumps, representing the hinder limbs. As Lan- kester claims, these two forms represent two stages of degeneration or atrophy of the limbs; ‘they have, in fact, been derived from the five-toed, four-legged ordinary lizard. form, and have nearly or almost lost the legs once possessed by their ancestors.” The entire order of snakes is an example how the loss, by atrophy, of the limbs may become common to an entire group of animals numbering thousands of species; the possession by the boas of a rudimentary pelvis, and minute but nearly atrophied hind legs, tends to prove that all the snakes are descendants from some ancestral form whose limbs became lost through disuse. Among the Diptera, which have but a single pair of wings, there is an universal atrophy of the second or hinder pair of wings; moreover, there are numerous wing- less, degraded forms, and when we take into account the fact that almost all dipterous larve are nearly headless and evidently degenerated forms, we are inclined to think that the entire group of true flies, numbering at least twenty thousand species, are the result of a retrograde development, affecting in every species the hinder pair of wings, and in numerous other forms the mouth-parts and other portions of the body, both in the larval and adult states. The group of barnacles (Cirripedia) is another example where atrophy and degeneration pervade each member of an order, and the cases are highly: interesting and suggestive. An entire sub-kingdom of animals may be degenerated in some respects. Such is the branch or sub-kingdom of sponges; the adult forms of which, by becoming fixed, have undergone a retrograde development, the gastrula or larval forms showing a promise of a state of development which the organism not only does not attain, but from which it falls completely away in after life. Lankester regards the acepha- lous molluscs, or bivalves, as having degerierated from a higher type of head-bearing active creatures like the snails. The ascidians start in the same path of development as the vertebrates, and at length fall back and lose nearly every trace of a vertebrate alliance. Besides sub-kingdoms, classes, and orders of animals, we have minor groups which are in their entirety examples of a backward development. Without doubt certain human races, as the present descendants of the Indians of Central America, the mod- ern Egyptians, “the heirs of the great Oriental monarchies of pre-Christian times,” the Fuegians, the Bushmen, and even the Australians, may be degenerate races. Lankes- ter, in his book on “ Degeneration,” considers the causes of retrograde development xvi THE ANIMAL KINGDOM. to be due to—1, parasitism; 2, fixity or immobility of the animal; 3, vegetative nutrition, and 4, excessive reduction in the size of the body. ANALOGY AND HomoLoey. When we compare the wing of an insect with that of a bird, and see that they are put to the same use, we say that they are analogous; for when we carefully compare the two organs, we see how unlike throughout they are. When we compare the fin of a whale with the fore-leg of a dog or bear, we see that one is adapted for swimming, and the other for running on dry land; but, however unlike the two limbs are superfi- cially, we find, on dissection, that all the principal bones and muscles, nerves and blood- vessels of the one correspond to those in the other, so that we say there is a structu- ral resemblance between the two kinds of limbs. Thus analogy implies a dissimilarity of structure in two organs, with identity in use, while homology implies blood-relation- ship. Analogy repudiates any common origin of the organs, however physiologically alike. In the early days of zoological science, but little was said about homologies; but when comparative anatomy engaged the attention of philosophical students, attention was given to tracing the resemblances between organs superficially and functionally unlike. It was found that the world of life teemed with examples of homologous parts. Afterwards, when the theory of evolution became the most useful tool the compar- ative anatomist could wield, and when the knowledge of comparative embryology completed his equipment, the most unexpected homologies were discovered. Of course, the more nearly related are the two anintals possessing homologous organs, as the dog and whale, the closer and more plainly homologous are their fore limbs. It is easy to trace the homologous organs in animals of the same order or class, however effectually degeneration on the one hand, or differentiation on the other, have done their work. But it was then found that the branchial sacs of ascidians are homologous with the pharyngeal chamber of the lamprey eel; that the position of the nervous system in ascidians accords morphologically with that of fishes and higher vertebrates; that the notocord of larval ascidians is the homologue of that of the lancelet and lam- prey, as well as that of embryo vertebrates in general; and, finally, the homologies between the larval ascidians and vertebrates are so startling that many comparative anatomists now maintain that the ascidians belong, with the vertebrates, to a common branch of the animal kingdom called Chordata. On the other hand, excellent anato- mists trace homologies between certain organs in worms, and corresponding organs in sharks and other vertebrates ; the segmental organs of worms have their homologous parts in the urogenital organs of sharks; the worm Balanoglossus has a respiratory chamber homologous with that of the lancelet and lamprey. Hence it came to pass that these general homologies between the lower, less specialized classes of inverte- brates, particularly the worms, and the lower vertebrates, were so many proofs of the origin of the latter from worms or worm-like forms. Hence the opinion now preva- lent that a homology between organs, however unlike in the uses at present made of them, implies that the animals having such organs had a common ancestry. Hence, also, the proofs of the unity of organization of the animal kingdom are based on a profound study of the resemblances in the tissues and organs of animals, rather than of their superficial, recently-acquired differences. INTRODUCTION. XVii Homology may be general or special; the latter limited, for the most part, to animals of the same sub-kingdom. It is well to use words which will express our meaning exactly, and hence a general homology may be indicated by the word isogeny, indicating a general similarity of origin; thus, the nervous system of worms, arthropods, molluscs, and vertebrates are isogenous, all being derivations of the epiblast. The term homology should be restricted to those cases where the correspondence, part for part, is more exact. Thus, the brain of fishes and that of man are not only isogenous, but homologous. Tuer ScaLE oF PERFECTION IN ORGANS AND IN ANIMALS. The history of the rise and progress of the human arm, possibly, as some claim, from an organ like the fin of a shark, a boneless, flabby limb; how it gradually, by adaptation, became like the differentiated fore-leg of a salamander, then became adapted for a climbing, arboreal use, and finally became, next to his brain, the most distinctive organ in man, — the history of the successive steps in this rise in the scale of perfec- tion would throw light on the general subject of the gradual perfection of organs and organisms. On the other hand, the hinder extremities or legs of man have not been equally perfected. As Cope has remarked: “ He is plantigrade, has five toes, separate carpals and tarsals, a short heel, rather flat astragalus, and neither hoofs nor claws, but something between the two.” Man’s limbs are not so extremely specialized as those of the horse, which is digitigrade, walking only on four toes, one to each foot. Man’s stomach is simple, not four-chambered, as in the ox. Thus one organ, or one set of organs, may in man attain the highest grade in the scale of perfection, while others may be comparatively low in form and function. Animals acquire, so to speak, their form by the acceleration in the growth of certain parts, which involves a retardation in the development of others; it is by the unequal development of the different parts that the fish has become adapted to its life in the water, that the bird becomes fitted for its aerial existence, and that moles can burrow, and monkeys are enabled to climb. The scale of perfection, as applied to organs, is a relative one; those in each animal are most perfect which are best adapted to subserve the requirements of that creature. Man’s brain is on the whole the most perfect of all organs, and it enables him to regu- late the movements of his limbs and other organs in a manner alone characteristic of an intellectual, reasoning, speaking, spiritual being. GENERALIZED AND SPECIALIZED TYPES. A large proportion of the higher classes of animals now living are more or less specialized ; they stand at or near the head of a series of forms which have become extinct, and which were much less specialized. For example, there are now living nearly ten thousand species of bony fishes, while the remains of only about twenty species have been found in the cretaceous formation. The earlier types of fishes were generalized or composite in their structure, presenting, besides the cartilaginous skeleton, a feature occurring in the embryos of lung fishes, characteristics which place them above the bony fishes. Among fishes, the lung fishes or Dipnoi, are the clearest example of a generalized type; they have a notocord, in which respect they resemble the lancelet and lamprey; while they possess one or two lungs, in which respect they resemble the salamanders or batrachians; thus in some features they are lower, and in others higher, than any of the bony fishes. There is a strange mixture of characters in these composite animals, and the living forms may be regarded as old-fashioned, Xviii THE ANIMAL KINGDOM. archaic types, the survivors of a large group of Devonian forms. They were called by Agassiz prophetic types, as they pointed to the coming of more highly wrought, specialized forms, the amphibians. They are now regarded as ancestral forms from which have originated two lines of organisms, one culminating in the bony fishes, and the other in the labyrinthodonts and salamanders and other batrachians. The king or horse-shoe crab (Limulus) is likewise a composite, synthetic, compre- hensive or generalized type, as it is variously called. Its development and structure shows certain features closely resembling the Arachnida, while it is also closely allied by other points to the Crustacea, with other features peculiar to itself. Its position in the scheme of nature is now in dispute, owing to the admixture of characters in which it resembles both the Crustacea and Arachnida. Now Limulus is a survivor or remnant of a long line of forms which flourished in the paleozoic seas, at a time when there were no genuine Crustacea nor Arachnida, which did not arise until long after the Merostomata (Zurypterus, etc.) and their allies, the trilobites, began to disappear. These generalized, composite arthropods lived, had their day, and finally gave way to the hosts of highly specialized modern Crustacea, such as the shrimps and crabs of our seas, and to the scorpions and spiders inhabiting the land, and which owe their diver- sity of form to the highly wrought structure of a few special parts. So, among insects, the earlier were the more generalized, old-fashioned forms. Such were the white ants, cockroaches, grasshoppers, may-flies and dragon-flies, the earliest insects known. Their numbers are scanty at the present day. They have been in part supplanted by the thousands of species of beetles, moths, butterflies, ants, wasps, and bees, so characteristic of the present age of the world as compared with the insect life of the carboniferous period. Among mammals the horse is the most specialized; its generalized ancestors were the Coryphodon and Kohippus. The latter had four usable toes, and the rudiments of a fifth on each forefoot, and three toes behind. The history of the horse family is a record of successive steps by which a highly specialized type was produced, culmina- ting in that extreme form, the American trotting horse, which can only do one thing well, ¢.¢. excel in trotting over a racecourse. PHYSIOLOGY. The most difficult line of study in biology is to determine how the organs do their work. This is the office of the physiologist. It is comparatively easy to discover how a fish uses its fins in swimming, how a mammal walks, how a bird flies; but it is diffi- cult to ascertain how the internal organs perform their functions; how the stomach digests food, exactly what office the biliary and pancreatic fluids fill in the compli- cated process of digestion; the function of the spleen, and so on with the other viscera. Here, besides observation and comparison, the physiologist has to rely on experiments to test the results of his observations. The pathway to a complete understanding of human physiology lies through the broad and as yet only partially surveyed field of animal physiology. We can better understand the physiology of digestion in man by studying the process of intracellular digestion in the Infusoria, the sponges, and jelly-fish, where, owing to the transparency of the tissues, the process can be actually observed ; so likewise, the nature of muscular movements can best be understood by observing under the microscope the contractility of the protoplasm of individual cells or one-celled organisms. The physiology of reproduction could never have been INTRODUCTION. xiv understood without a study of the operations of cell-division, self-fission and gemma- tion in the one-celled animals and polyps. Our most eminent human physiologists, such as Remak, Bischoff, von Baer, and others, have had to go to the lower animals for facts to illustrate the reproductive processes in man. No medical student can in these days afford to be ignorant of the general laws of animal physiology. Locomotion. All the movements of the body, or of the internal organs, with which physiology has to do, depend primarily on the contractility inherent in the protoplasm filling the cells of the body. Of the cause of contractility in protoplasm we know nothing. We see its manifestations in the irritability and resulting contractions of the body of the Ameba, of the white blood-corpuscle, and other cells and one-celled organisms. It is this inherent contractility of the protoplasm in muscle-cells which gives rise to muscular movements. But the simplest one-celled animals do not move about by means of muscles. The Ameba changes its position, Proteus-like, by variously contracting the body, and thus changing its form, throwing out root-like processes in different directions. The Infusoria have permanent thread-like processes, called cilia, by which they can swim about in the water. In the Hydra and other polyps, however, we meet with muscles, by which the body can contract in certain parts; in such animals the base of the body forms a more or less contractile, movable, creeping disc, while the tentacles move partly by means of their muscular walls, and partly mechanically by filling them with the circulatory fluid of the body. The sea-urchin and starfish move slowly over the sea weed and rocks by means of long, slender suckers. Extending these by allowing the water to flow into them, and fastening them to the surface of the object over which they are moving, they then contract them, and in this way the body is warped slowly along. In the lower worms, such as the flat-worms, or in the snails, the gliding movement is due to the muscular contractions of the under side of the body. The gliding motion of snails is due to a system of extensive muscular fibres within the disc, which act when the sinuses within the disc are filled with blood; their extension causing the undulating appearance on the under side of the snail’s foot, or creeping disc; but the snail can only thus move forwards; the lateral movements and shortening of the foot being produced by oblique muscular fibres. Rising in the zoological scale, we come to the Crustacea and insects with have jointed legs, ending, in the latter, in claws adapting the limb both for walking and climbing. The legs of arthropods are perhaps modifications of the lateral fleshy oar-like appendages of the sea-worms, which have become externally hard and jointed, with several leverage-systems. The mechanism of locomotion is fundamentally the same in the legs of arthropods and vertebrates. Space does not permit us to discuss the subject of the mechanism of walking, running, and flying, but all these movements are dependent primarily on the contractility inherent in the protoplasm filling the cells forming muscular tissue. DicEstIon. The most important organs in the animal system are those relating to digestion, as an animal may respire solely through its body-walls, or do without a circulatory or nervous system, but must eat in order to live and grow. The opening by which the xx THE ANIMAL KINGDOM. food is taken into the alimentary canal is called the mouth, whether reference is made to the ‘mouth’ of a hydra or of a vertebrate. Although the structure of the edges may differ radically, still in most Metazoa the mouth is due to an inpushing of the ec- toderm, however differently the edge may be supported and elaborated. The edges of the mouth are usually called the lips, but true lips for the first time appear in the Mammalia. The trituration or mastication of the food is accomplished among the in- vertebrates in a variety of ways, and by organs not always truly homologous. The object of digestion is to reduce the food into a convenient condition, and to dissolve or to transform it into tissue-food. How the products of digestion are carried about in the body, so as to supply the tissues of the various organs, by the circulatory organs, will be pointed out in the next section. The simplest form of the digestive process may be seen by a skilled observer in the cells lining the digestive pockets or chambers in the interior of a sponge or jelly-fish. Each cell has a certain amount of individuality, taking in, through transitory openings in their walls, particles of food, and rejecting the waste portions, much as individual Infusoria, which have no stomachs, in- gest their food, and reject the particles which are indigestible or not needed. Not only has intra-cellular digestion, as it is called, been observed in sponges and jelly-fishes, as well as in ctenophores, but also in low worms (Turbellaria). We will now look at the leading steps in the evolution and specialization of the di- gestive cavity of animals. In the polyps, such as Hydra and Coryne, it is simply a hollow in the body. The Hydra draws some little creature with its tentacles into its stomach ; there it is acted upon by the juices secreted by the walls of the stomach, and the hard parts rejected from the mouth. For the technical name of the digestive tract as a whole, we may adopt Haeckel’s term enteron. In the jelly-tishes the stomach opens into four or more water-vascular canals or passages, by which the food, when partially digested and mixed with sea-water, thus forming a rude sort of blood, supplies the tissues with nourishment. In the sea-anem- ones and coral polyps, the digestive cavity is still more specialized, and its walls are partly separated from the walls of the body, though at the posterior end the stomach opens directly into the body cavity. In the echinoderms and worms do we find for the first time a genuine digestive tube, lying in the perivisceral space (which, with Haeckel, we may call the celom), and opening externally for the rejection of waste matter. In the worms the digestive canal becomes separated into a mouth, an cesophagus, with salivary glands opening into the mouth, and there is a division of the diges- tive tract into three regions —¢. e., fore (esophagus), middle (chyle-stomach), and hind enteron (intestine). In the molluscs and higher worms there is a well-marked sac-like stomach and an intestine, with a liver, present in certain worms and in the ascid- ians and molluscs, opening into the beginning of the intestine. All these divisions of the digestive tract exist still more clearly in the Crustacea and most insects. In the latter, six or more excretory tubes (Malpigian vessels) discharge their contents into the intestines, and in the ‘respiratory tree’ of the Holothurian, and the segmental organs of certain worms we have organs with probably similar excretory uses. In the vertebrates, from the lancelet to man, the alimentary canal has, without exception, the three divisions of esophagus, stomach, and intestine, with a liver. In this branch the lungs are modified parts of originally sac-like dilatations of the first divi- sion of the digestive tract. The intestine is also sub-divided in the mammals into the small and large intestine and rectum, a cecum being situated at the limits between the INTRODUCTION. xxi small and large intestine. We thus observe a gradual advance in the degree of spe- cialization of the digestive organs, corresponding to the degree of complication of the animal. — (Packard’s Zoology.) We will now look at the glands which pour their secretion into the digestive canal. Tn the worms, salivary glands send their secretion into the throat, while in the polyps (ceelenterates) and many worms, and in all insects the stomach is lined with a layer of colored cells which secrete bile; in the spiders the stomach forms a set of complicated cecal appendages which secrete a fluid like bile ; in the Crustacea, and lower molluses, there is a liver formed of little glands which open into the beginning of the intestine, while in the higher molluscs and in the vertebrates we have a true specialized liver merely connected with the digestive canal by its ducts. Thus the original food-stuff is variously treated by animals of different grades. In the sea-anemone or any polyp, a very imperfectly digested material is pro- duced, which is taken at first hand, mixed with the sea-water, and in part churned by the movements of the body, in part moved about in a more orderly and thorough manner, in currents formed by the cilia lining the chambers of the body. In the worms, and insects, etc., the chyle or products of digestion percolates, or oozes through the walls of the intestine into the body cavity, and there directly mingles with the blood, and is thus carried in the circulation to every part of the body, however remote or minute. In the vertebrates, however, this is not so. The chyle, a much more elaborate fluid than that of the lower animals, is carried by an intricate system of vessels, called lymphatics, from the intestine to the blood vessels. Thus the process of digestion becomes increasingly elaborate as we ascend in the animal series, and as the digestive system becomes more and more complex. Here again we might look at the chewing apparatus or teeth, arming the mouth, by which the food is made ready for digestion. To quote from the author’s text-book of Zoology :— Hard bodies serving as teeth occur for the first time in the animal series in the sea-urchins, where a definite set of. calcareous dental processes or teeth, with solid ‘supports and a complicated muscular apparatus, serves for the comminution of the food, which consists of decaying animals and sea-weeds. In those echinoderms which do not have a solid framework of teeth, the food consists of minute forms of life, proto- zoans and higher soft-bodied animals, or the free-moving young of higher animals, which are carried into the mouth in currents of water or swallowed bodily with sand or mud. Among the worms, true organs of mastication for the first time appear in the Rotatoria, where the food, such as Infusoria, etc., is crushed and is partly comminuted by the well-marked horny and chitinous pieces attached to the mastax. In most other low worms the mouth is unarmed. In the leeches there are three, usually in the annelids two, denticulated or serrate, chitinous flattened bodies, situated in the exten- sible pharynx of these worms, and suited for seizing and cutting or crushing their prey. In the higher molluscs, such as the snails (Cephalophora) and cuttles, besides one or more broad, thin pharyngeal jaws, comparable with those mentioned as existing in the worms, is the lingual ribbon, admirably adapted for sawing or slicing sea-weeds, and cutting and boring into hard shells, acting somewhat like a lapidary’s wheel; this organ, however, is limited in its action, and in the cuitles, the jaws, which are like a parrot’s beak, do the work of tearing and biting the animals serving as food, which are seized and held in place by the suckered arms. xxii . THE ANIMAL KINGDOM. In. the crustaceans and insects we have an approach to true jaws, but here they work laterally, not up and down, or vertically, as in the vertebrate jaws; the mandi- bles of these animals are modified feet, and the teeth on their edges are simply irregularities or sharp processes, adapting the mandibles for tearing and comminuting the food. It is generally stated that the numerous teeth lining the crop of Crustacea and insects, serve to further comminute the food after being partially crushed by the mandibles, but it is now supposed that these numerous points also act collectively as a strainer to keep the larger particles of food from passing into the chyle-stomach until finely crushed. The king-crab burrows in the mud for worms (Nereids, etc.); these may be found almost entire in the intestine, having only been torn here and there, and partly crushed by the spines of the base of the foot-jaws, which thus serve the purpose effected by the serrated edges of the mandibles of the genuine Crustacea and insects. Among vertebrates the lancelet is no better off than the majority of the cclen- terates and worms, having no solid parts for mastication; and the jaws and teeth of the hag-fish, and even the lamprey eel, form a very different apparatus from the jaws and its skeleton in the higher vertebrates; and even in the latter the bony elements differ essentially in form in the different classes, though originating in the same man- ner in embryonic life. In the birds, the jaw-bones are encased in horny plates; true tecth being absent in the living species, the gizzard being, however, provided with two hard grinding surfaces; on the other hand, mammals without teeth are excep- tional, The teeth of fishes are developed, not only in the jaws, but on the different bones projecting from the sides and roof of the mouth, and extend into the throat. In many cases, in the bony fishes, these sharp recurved teeth serve to prevent the prey, such as smaller fish, from slipping out of the mouth. On the other hand, the upper and lower sides of the mouth of certain rays (A/yliobatis) are like the solid pavement of a street, and act as an upper and nether mill-stone to crush solid shells. In the toothless ant-eaters the food consists of insects, which are swallowed with-. ‘out being crushed in the mouth; true teeth are wanting in the duck-bill, their place being taken by the horny processes of the jaws, while in Steller’s manatee the toothless jaws were provided with horny solid plates for crushing the leaves of succu- lent aquatic plants. Examples of the most highly differentiated teeth in vertebrates are seen in those animals which, like the bear, are omnivorous, feeding on flesh, insects, and berries, and which have the crown of the molars tuberculate; while the canines are adapted for holding the prey firmly as well as for tearing the flesh, and the incisors for both cutting and tearing the food. CIRCULATION. Intimately associated with the digestive canal are the vessels in which the pro- ducts of digestion mix with the blood and supply nourishment for the tissues, or, in other words, for the growth of the body. In the Infusoria the evident use of the con- tractile vesicles is to aid in the diffusion of the partly digested food of these micro- scopic forms. In the Hydra the food stuff is directly taken up by the cells lining the celom, while the imperfectly formed blood also finds access to the hollows of the tentacles. The mode in which the cells lining the canals in the sponge take up, by means of pseudopodia, microscopic particles of food, directly absorbing them in their substance, is an interesting example of the mode of nourishment of the cellular tissues INTRODUCTION. xxiii of the lower animals. The sea-anemone presents a step in advance in organs of circu- lation; here the partly digested food escapes through the open end of the stomach into the perivisceral chambers formed by the numerous septa, the contractions of the body churning the blood, consisting of sea-water and the particles of digested food, and a few blood-corpuscles, hither and thither, and with the cilia forcing it into every interstice of the body, so that the tissues are everywhere supplied with food. The water-vascular system of the celenterates presents an additional step in de- gree of complexity; but it is not until we reach the echinoderms, on the one hand, and such worms as the Vemertes and its allies on the other, where definite tubes or canals, the larger ones contractile, and, in the latter type at least, formed from the mesoderm, serve to convey a true blood to the various parts of the body, that we have a definite blood system. In the echinoderms a true hemal or vascular system may co- exist with the water-vascular system. In the annelids, such as the Wereis, one of the blood-vessels may be modified to form a pulsating tube or heart, by which the blood is directly forced outward to the periphery of the body through vessels which may, by courtesy, be called arteries, while the blood returns to the heart by so-called veins. The molluscs have a circulatory system which presents a nearer approach to the vertebrate heart and its vessels than even in the crustaceans and insects, for the ven- tricle and one or two auricles, with the complicated arterial and venous system of vessels of the clam, snail, and cuttle-fish, truly foreshadow the genuine heart and sys- temic and pulmonary circulation of the vertebrates. The molluscs, and king-crab, and the lobster, possess minute blood vessels which present some approach to the capillaries of vertebrates. The circulation in certain worms, from Memertes upward, may be said to be closed, the vessels being continuous; but they are not so in insects where true veins are not to be found, the blood returning to the heart in channels or lacune in the spaces between the muscles and viscera. _ In vertebrates the ‘aortic heart’ of the lancelet or Amphioaus is simply a pulsat- ing tube, and there are portions of other vessels which are pulsatile, so that there is, as in some worms, a system of ‘hearts.’ A genuine heart, consisting of an auricle and a ventricle only, first appears in the lamprey. This condition of things survives in fishes, with the exception of those forms, such as the lung-fish (Dipnoans), whose heart anticipates in structure that of the amphibians and reptiles, in which a second auricle appears. Again, certain reptiles, such as the crocodiles, anticipate the birds and mammals in having two ventricles— 7. e., a four-chambered heart. It should be borne in mind that in early life the heart of all skulled vertebrates (Craniota) is a simple tube, and as Gegenbaur states, “as it gradually gets longer than the space set apart for it, it is arranged in an S-shaped loop, and so takes on the form which the heart has later on.” Owing to this change of form it is divided into two parts, the auricle and ventricle. A striking feature first encountered in the craniate vertebrates is the presence of a set of vessels conveying the nutrient fluid or chyle which filters through the walls of the digestive canal to the blood-vessels; these are, as already stated, the lymphatics. In the lancelet, as well as in the invertebrate animals, such vessels do not occur, but the chyle oozes through the stomach-walls and directly mixes with the blood. RESPIRATION. Always in intimate relation with the circulatory system are the means of respira- tion. The process may be carried on all over the body in the simple animals, such XxXiv THE ANIMAL KINGDOM. r as Protozoa or sponges, or, as in colenterates, it may be carried on in the water- vascular tubes of those animals, while in the so-called respiratory tree of echin- oderms it may go on in company with the performance of other functions by the same vessels. Respiration, however, is inclined to be more active in such finely subdivided parts of the body as the tentacles of polyps, of worms, or any filamentous subdivisions of any of the invertebrates; these parts, usually called gills, present in the aggregate a broad respiratory surface. Into the hollows of these filamentous processes, which are usually extensions of the body-walls, blood is driven through vessels, and the oxygen in the water bathing the gills filters through the integument, and immediately gains access to and mixes with the blood. The gills of the lower animals appear at first sight as if distributed over the body in a wanton manner, appearing in some species on the head, in others along the sides of the body, or in others on the tail alone; but in fact they always arise in such situations as are best adapted to the mode of life of the creature. The gills of many of the lower animals afford an admirable instance of the econ- omy of nature. The tentacles of polyps, polyzoans, brachiopods, and many true worms serve also, as delicate tactile organs, for grasping and conveying food to the mouth, and often for locomotion. The suckers or ‘feet’ of star-fish or sea-urchins also without doubt help to perform the office of gills, for the luxuriously branched, beautifully-col- ored tentacles of the sea-cucumber are simply modifications of the ambulacral feet. In the molluscs, especially the snails and cuttle-fish, the gills are in close relations with the heart, so that in the cuttle-fish the auricles are called ‘ branchial hearts.’ The gills of crustaceans are attached either to the thoracic legs or are modified abdominal ‘feet, being broad, thin, leaf-like processes into which the blood is forced by the con- tractions of the tubular heart. Respiration in the insects goes on all over the interior of the body, the tracheal tubes distributing the air so that the blood becomes oxyge- nated in every part of the body, including the ends of all the appendages. The gills of aquatic insects are in all cases filamentous or leaf-like expansions of the skin permea- ted by trachese; they are, therefore, not strictly homologous with the gills of crusta- ceans or of worms. — (Packard’s Zoology.) We now come to the respiratory organs of the vertebrates, which are in close rela- tion to the digestive canal. First the gills: just behind the mouth are openings, called branchial clefts, on the edges of which arise processes, the gills or branchie. Through- out these gills are distributed minute arteries and veins, forming a network; the gills are bathed in water taken in through the mouth. In the amphibians and lung-fishes, (Dipnoi) lungs, which are outgrowths of the enteric canal, replace the swimming bladder of the fishes, the air being now swallowed by the mouth and gaining access by a special passage, the larynx, to highly specialized organs of respiration, the lungs, which are situated in the thoracic cavity near the heart. NERVES AND SENSATION. We have seen that animals of comparatively complicated structure perform their work in the animal economy without any nervous system whatever. In none of the Protozoans, even the highest infusorians, have true nerve-cells been yet detected; in these animals the tissues are in an inchoate, non-specialized state. It is not until we rise to the many-celled animals that we observe nerves and nerve-centres. It has been only recently discovered that in many jelly-fish there is, for the first time in the ani- mal series, a true nervous system, with definite nerve-centres or ganglia. In the INTRODUCTION. XXV hydroids none has been found, so that the majority, if not all, of the polyps per- form their complicated movements, capturing and taking in food, digesting it, and reproducing their kind, without the aid of what seems, when we study vertebrates alone, as the most important and fundamental system of organs in the body. The Protozoa, sponges, and many celenterates depend, for the power of motion, on the irritability and ‘contractility of the protoplasm of the body, whether or not separated into muscular tissue. Referring to the complicated movements of the Pro- tozoa, Dr. Krukenberg well says: “The changeful phenomena of life, which we remark in the smallest organisms—in the rhythm of their ciliary motions, now strengthened, now slackened; in the rhythmic alternation of the capacity of their contractile vesicles; in their regulated incomes, deposits, and expenditure; in the abundance of the visible products of their diverse material exchanges — enable us but remotely to foresee what is here effected by a harmonious co-operation of countless processes limited to the smallest space. Let their formal differentiation seem to us ever so slight, just so do these beings become for us all the greater riddles, especially when we find in them vital manifestations elsewhere displayed in the living world only by apparatus of the most highly complex constructions, and in them meet with processes which, without the orderly co-operation of very different factors, must remain to us unintelligible.” In the Hydra for the first time appear the traces of a nervous tissue in the so-called neuro-muscular cells, one portion of a cell being muscu- lar, the other nervous in its functions. A more definite nervous organization has been detected in the Actiniw, in the form of disconnected bodies and rod-like nerve cells, and other nervous bodies found near the eye-spots, and the nerve-cells and fibres at the base of the body; but a genuine nervous system for the first time appears in certain naked-eyed jelly-fishes, in which it is circular, sharing the radiated disposition of parts in these animals. As the results of his experiments on the ctenophores, Krukenberg finds that animals of this class, of comparatively simple structure, and therefore exhibiting morphological differ- ences which to us seem trifling, may nevertheless display very diverse reactions when exposed to similar abnormal conditions in the physiological laboratory. “In our attempt to explain the occult vital powers thus revealed, we are debarred from an appeal to the apparently corresponding diversities sometimes encountered in the case of the much more complex vertebrates.” The echinoderms have a well-developed nervous system, consisting of a ring (without, however, definite ganglia, though masses of ganglionic cells are situated in the larger nerves), surrounding the cesopha- gus, and sending a nerve into each arm; or, in the holothurians, situated under the longitudinal muscles radiating from that muscle closing the mouth. Recent researches on the star-fish show, however, that besides the ring around the mouth, and the five main nerves passing along the arms or rays, there is a thin nerve-sheath which encloses the whole body, and is directly continuous with the external epidermis, of which it forms the deepest layer. The circumoral and radial nerves are believed to be simply thickenings of this thin nervous sheet. In this connection should be mentioned the experiments made by Romanes, Ewart, and Marshall, on living Echini, “ which lead them to believe in the existence not only of an external nerve-plexus outside the test, but also of an internal plexus on its inner surface; they further believe that the two systems are connected by nerve-fibres run- ning through the plates of the test or shell.” Tn all other invertebrate animals, from the worms and Mollusca to the crustaceans ee THE ANIMAL KINGDOM. and insects, the nervous system is fundamentally built nearly upon the same plan. There is a pair of ganglia above the esophagus, called the ‘brain;’ on the under side is usually a second pair; the four, with the nerves or commissures connecting them, form- ing a ring. This arrangement of ganglia, often called the ‘esophageal ring,’ consti- tutes, with the slender nerve-threads leading away from them, the nervous system of the lower worms, in many of which, however, as also in most Polyzoa and Brachio- poda, the subesophageal ganglia are wanting. Now to the esophageal ring with its two pairs of ganglia, add a third pair, the visceral ganglia, and we have the nervous system of the clam and many molluscs. Tn the higher ringed worms, the Annulata, and in the Crustacea and Insects, there is a chain of ganglia, or brains, which, behind the throat, are ventral, and lie on the floor of the ceelom or body cavity. The highest form of nerve-centre found in the invertebrate animals, and which hints at the brain and skull of vertebrates, is the mass of ganglia partly enclosed in an imperfect cartilaginous capsule in the head of the cephalopods. The nervous cord of the Appendicularia, an ascidian, is con- structed on the same plan as in the Annulata, but the mode of origin and apparently dorsal position of the nervous system of the tailed larval ascidian presents features which apparently anticipate the state of things existing among the lower vertebrates, such as the lancelet. We need not here describe the different forms of nervous system in the classes of invertebrates, but refer the reader to the figures and descriptions of the different types in the body of this work. It will be well to read the following data concerning the brain and nervous system, which we quote from Bastian’s “The Brain as an Organ of Mind.” “1. Sedentary animals, though they may possess a nervous system, are often head- less, and they then have no distinct morphological section of this system answering to what is known as a brain. “2. When a brain exists, it is invariably a double organ. Its two halves may be separated from one another, though at other times they are fused into what appears to be a single mass. “3. The component or elementary parts of the brain in these lower animals are ganglia in connection with nerves proceeding from special impressible parts or sense- organs; and it is through the intervention of these united sensory ganglia that the animal’s actions are brought into harmony with its environment or medium. “4, That the sensory ganglia, which in the aggregate constitute the brain of invertebrate animals, are connected with one another on the same side, and also with their fellows on the opposite sides of the body. They are related to one another either by what appears to be continuous growth, or by means of ‘commissures.’ “5, The size of the brain as a whole, or of its several parts, is therefore always fairly proportionate to the development of the animal’s special sense-organs. The more any one of these impressible surfaces or organs becomes elaborated and attuned to take part in discriminating between varied external impressions, the greater will be the proportionate size of the ganglionic mass concerned. “6, Of the several sense-organs and sensory ganglia whose activity lies at the root of the instinctive and intelligent life (such as it is) of invertebrate animals, some are much more important than others. Two of them especially are notable for their greater proportional development, viz.: those concerned with touch and vision. The organs of the former sense are, however, soon outstripped in importance by the latter. INTRODUCTION. XXVii The visual sense, and its related nerve-ganglia, attain an altogether exceptional devel- opment‘in the higher insects and in the highest molluscs. “7, The sense of taste and that of smell seem, as a rule, to be developed to a much lower extent. In the great majority of invertebrate animals it is even difficult to point to distinct organs or impressible surfaces as certainly devoted to the reception of either of such impressions. Nevertheless there is reason to believe that in some insects the sense of smell is marvellously keen, and so much called into play as to make it for such creatures quite the dominant sense endowment. It is pretty acute also in some Crustacea. “8, The sense of hearing seems to be developed to a very slight extent. Organs ‘supposed to represent it have been discovered, principally in molluscs and in a few insects. It is, however, of no, small interest to find that where these organs exist the nerves issuing from them are most frequently not in direct relation with the brain, but immediately connected with one of the principal motor nerve-centres of the body. It is conjectured that these so-called ‘auditory saccules’ may, in reality, have more to do with what Cyon terms the sense of space than with that of hearing. The nature of the organs met with supports this view, and their close relations with the motor ganglia also become a trifle more explicable in accordance with such a notion. “9. Thus the associated ganglia representing the double brain are, in animals pos- sessing a head, the centres in which all impressions from sense-organs, save those last referred to, are directly received, and whence they are reflected on to different groups of muscles—the reflection occurring not at once, but after the stimulus has passed through certain ‘motor’ ganglia. It may be easily understood, therefore, that in all invertebrate animals perfection of sense-organs, size of brain, and power of executing manifold muscular movements, are variables intimately related to one another. “10. But a fairly parallel correlation also becomes established between these various developments and that of the internal organs. An increasing visceral com- plexity is gradually attained ; and this carries with it the necessity for a further devel- opment of nervous communications. The several internal organs with their varying states are gradually brought into more perfect relation with the principal nerve-cen- tres as well as with one another. “11. These relations are brought about by important visceral nerves in Vermes and arthropods— those of the ‘stomato-gastric systems’ — conveying their impres- sions either direct to the posterior part of the brain or to its peduncles. They thus constitute internal impressions which impinge upon the brain side by side with those coming through external sense-organs. “12, This visceral system of nerves in invertebrate animals has, when compared with the rest of the nervous system, a greater proportional development than among vertebrate animals. Its importance among the former is not dwarfed, in fact, by that enormous development of the brain and spinal cord which gradually declares itself in the latter. “13. Thus impressions emanating from the viscera and stimulating the organism to movements of various kinds, whether in pursuit of food or of a mate, would seem . to have a proportionally greater importance as constituting part of the ordinary mental life of invertebrate animals. The combination of such impressions with the sense- guided movements by which they are followed, in complex groups, will be found to afford a basis for the development of many of the instinctive acts which animals so frequently display.” XXVili THE ANIMAL KINGDOM. When we rise to the vertebrates we meet with a form of nervous system quite different from that of any adult invertebrate animal. In all the vertebrates which have a definite skull—and this only excludes the lancelet and the ascidians — the brain is a series of close-set ganglia, forming a mass situated in the skull, with definite relations to the sense-organs, and the spinal cord is situated above the vertebral col- umn, passing through the spinal canal, which is formed by the contiguous posterior arches of the several vertebrae composing the spinal, or vertebral column. While the nervous system of all skulled vertebrates has a definite persistent situa- tion, and with a similar cellular structure, there is a great ditference between the brain of the fishes and that of mammals, including man. In the fishes the brain cavity is small compared with the size of tlie head, the brain being small, and there is a marked equality in the size of the different lobes forming the brain, the optic lobes being larger than the cerebral. In amphibians, such as the frog and toad, the brain is more like that of fishes than of reptiles, but the optic lobes are a little smaller than the cerebral, while the cerebellum is smaller than in many fishes. In the reptiles, as seen in snakes, turtles, and crocodiles, the cerebral lobes begin to enlarge, and exceed in size the optic lobes. Here the ventricle or cavity of the cerebral lobes is larger than in the fishes, and the rounded eminence projecting from its anterior and inner ‘surface, called the ‘corpus striatum,’ is present for the first time. In birds the brain cavity is much larger than in any of the foregoing classes of vertebrates, and the cerebral hemispheres are now greatly increased in size, so as to partly cover the optic lobes. The cerebellum is also much larger than before, and it is transversely creased. Passing from the birds to mammals, there is seen to be a great advance in the form of the brain of the latter animals. The brain cavity is much larger, and this is for the most part occupied by two portions, the cerebrum and the cerebellum. The cerebral hemispheres entirely conceal from above the olfactory and optic lobes, the surface is ‘convoluted, while behind it either touches or overlaps, so as in man to completely conceal the cerebellum. The cerebral hemispheres, then, form the back of the mam- malian brain, and the higher orders are usually characterized by an increase both in the size of the cerebral hemispheres, and as a rule, though there are exceptions noted farther on, in the number and complexity of the convolutions of the surface. Thus in ‘the highest mammals, especially the gorilla and man, the increased size of the brain in proportion to the greater bulk of the body is very marked. Leuret has approximately shown the average proportional weight of the brain to the body, in four classes of vertebrates, as follows: in Fishes, as 1 to 5,668; in rep- tiles, as 1 to 1,321; in birds, as 1 to 212; in Mammalia, as 1 to 186. The brain is, however, subject to the same laws as cther parts of the body. There is in no organ a regular and continuous progressive increase in size and complexity in any class of the animal kingdom. The size of the cerebral hemisphere differs in different monkeys, and, as has been remarked by Bastian, in the higher types of lower orders the brain is often better developed than among the lower types of higher orders. Thus in the Midas marmoset the convolutions are absent, so that in this respect this primate is on a level with the monotremes and lower marsupials and rodents. In dwarf or small-sized members of a group the brain is larger in proportion to the body than in the full-sized -members. Thus among marsupials, as Owen states, the size of the brain of the pigmy petaurist is to the size of the body as 1 to 25, while in the great kangaroo it is as 1 to 800; among rodents it is as 1 to 20 in the harvest mouse, but is as 1 to 300 in the INTRODUCTION. XxIx capybara; among the Insectivora it is as 1 to 60 in the little two-toed ant-eater, but is as 1 to 500 in the great ant-eater. The brain of a porpoise four feet long may weigh 1 lb. avoirdupois; that of a whale (Balwnoptera) 100 feet in length does not exceed 4 Ibs. avoirdupois; in Quadrumana the brain of the Midas marmoset is to the body as 1 to 20; in the gorilla it is as 1 to 200. “But such ratios do not show the grade of cerebral organization in the mammalian class; that in the kangaroo is higher than that in the bird, though the brain of a sparrow be much larger in proportional size to the body: and the kangaroo’s brain is superior in superficial folding and extent of gray cerebral surface to that of the petaurist. The brain of the elephant bears a less proportion to the body than that of opossums, mice, and proboscidian shrews, but it is more complex in structure, more convolute in surface, and with proportions of pros- to mes-encephalon much more nearly than in the human brain. The like remark applies to all the other instances above cited.” Owen explains these facts by saying that the brain grows more rapidly than the body, and is larger in proportion thereto at birth than at full growth; “so in the degree in which a species retains the immature character of dwarfishness, the braimis relatively larger to the body.” The bearing of the facts known as to the relative size of the brain and the convolu- tions are thus discussed by Bastian: “There cannot therefore be, among animals of the same order, any simple or definite relation between the degree of the intelligence of the creature and the number or disposition of its cerebral convolutions —since this structural feature of the brain seems to be most powerfully regulated by the mere bulk of the creature to which it belongs.” It fails still more, when comparing representa- tives of different orders. For example, the beaver’s brain is almost smooth, while that of the sheep has numerous convolutions, which both in number and complexity decid- edly surpass even those of the dog. Yet among closely related animals and those of about the same size, especially in species of the same genus, or, as in the case of man, in individuals of the same species, we may look for some proportional relations between the development of their cerebral convolutions and their intelligence. “Size of brain, and with it convolutional complexity, must,” Bastian remarks, “ be closely related to the number and variety of an animal’s sensorial impressions, and also to its power of moving continually or with great energy. “The importance of taking into account the powers of movement possessed by the animal is fully borne out by the fact that the brain attains such a remarkable size in the shark, as well as in the porpoise and the dolphin—all of them creatures whose movements are exceptionally rapid, continuous, and varied. The great increase in the size of the cerebellum in each of these creatures is, therefore, not so surprising ; but it seems very puzzling, at first sight, to understand why this should be accompanied by a co-ordinate increase in the development of the cerebral hemispheres. For this, however, there are two causes, the one general and the other more special. It is a fact generally observed, that sensorial activity, and therefore intelligent discrimination, in- creases with an animal’s powers of movement; and secondly, there must be special parts of the cerebral hemispheres devoted to the mere sensory appreciation of move- ments executed. The nerve elements lying at the basis of this latter appreciation, -however they may be distributed through the hemispheres, would naturally be the more developed (and, consequently, all the more calculated to help to swell the size of the cerebrum), in proportion to the variety and continuance of the movements which the animal is accustomed to execute.” XXX THE ANIMAL KINGDOM. The tactile sense, or sense of touch is common to all animals; this is the most fun- damental sense, of which the other senses are without doubt differentiations. In the lower Protozoa, such as the Amoeba, the sense of touch which they appear to possess may be due to the inherent irritability and contractility of the protoplasm of which their bodies are formed. In the Infusoria, without doubt, the cilia and the flagella with which these animals are provided are not only organs of locomotion but also of touch. It is probable that none of the many-celled animals are without the sense of touch unless some of the sponges, and the root-barnacles (Sacculina) may be, by reason of their lack of a nervous system and otherwise degenerate structure, destitute of any sense whatever. The most important of the sense organs are undoubtedly eyes, as they are the most commonly met with. The transparent spot in the front of the body of Euglena viridis, a protophyte, may possibly be the simplest of all sense organs; if so, it anticipates the eye of animals. The simplest forms of eyes are perhaps those of the sea-anemone, in which there are, besides pigment cells forming a colored mass, refrac- tive bodies which may break up the rays of light impinging on the pigment spot, so that these creatures may be able to distinguish light from darkness. The next step in advance is where a pigment mass covers a series of refractive cells called crystalline rods or crystalline cones, which are situated at the end of a nerve proceeding from the brain. Such simple eyes as these, often called eye-spots, may be observed in the flat worms, and they form the temporary eyes of many larval worms, echinoderms, and mol- luscs. In some nemertean worms, such as certain species of Polia and Nemertes, true eyes appear, but in the ringed worm, Neophanta celox, Greef describes a remarkably perfect eye, consisting of a projecting spherical lens, covered by the skin, behind which is a vitreous body, a layer of pigment separating a layer of rods from the external part of the retina, outside of which is the expansion of the optic nerve. Eyes are also sit- uated on the end of the body in some worms, and in a worm called Polyophthaimus, each segment of the body bears a pair of eyes. The eyes of molluscs are, as a rule, highly organized, until in the cuttle-fish the eyes become nearly as highly developed as in fishes, but still the eye of the cuttle-fish is not homologous with that of vertebrates, since in the former the crystalline rods are turned towards the opening of the eye, while in vertebrates they are turned away from the opening of the eye, so that, as Huxley as well as Gegenbaur show, the homology between the eye of the cephalopods and of the vertebrates is not exact. While, as we have seen, the eyes of the worms and the molluscs are situated arbi- trarily, by no means invariably placed in the head, in the crustaceans the eyes assume in general a definite position in the head, except in a schizopod crustacean (Huphausia), where there are eye-like organs on the thorax and abdomen. In insects there are both simple and compound eyes occupying definitely the upper and front part of the head. The eyes of the lancelet are not homologous with those of the higher vertebrates, being only minute pigment spots comparable with those of the worms. In the skulled vertebrates the eyes are of a definite number, and in all the types occupy a definite position in the head. The simplest kind of auditory organ is to be found in jelly-fishes, where an organ of hearing first occurs. In these animals, situated on the edge of the disc, are minute vesicles containing one or more concretionary bodies or crystals. Reasoning by ex- clusion, these are supposed to represent the ear-vesicles or otocysts of worms and molluscs; and the concretions or crystals, the otoliths of the same kind of animals. INTRODUCTION. Xxxi The otocysts or simple ears of worms and molluscs are minute and usually difficult to find, as is the auditory nerve leading from them to the nerve-centres. In the clam it is to be looked for in the so-called foot. In the snails, as also in cuttle-fish, the auditory vesicles are placed in the head close to the brain. The ears of Crustacea are sacs, formed by inpushings of the integument and filled with fluid, into which hairs project, and which contain grains of sand which have worked in from the outside, or concretions of lime. These are situated in the shrimps and crabs at the base of the inner antenne, but in afew other Crustacea, as in Mysis, they are placed at the base of the lobes of the tail. In the insects the ear is a sac covered by a tympanum, with a ganglionic cell within, leading by a slender nerve-fibre to a nerve-centre, and in these animals the distribution of ears is very arbitrary. In the locust they are situated at the base of the abdomen; in the green grasshoppers, or katydids, and the crickets, in the fore tibiz ; and it is probable that, in the butterflies, the antennz are organs of hearing. The vertebrate ears are two in number, and occupy a distinct permanent position in the skull, however much modified the middle and outer ear become. — (Packard’s Zoology.) “ Throughout the animal kingdom,” says Romanes, “ the powers of sight and of hear- ing stand in direct ratio to the powers of locomotion;” on the other hand, in fixed or parasitic animals, the organs of hearing and sight are among the first to be aborted. The sense of smell is obscurely indicated by special organs in the invertebrate ani- mals; nasal organs, as such, being characteristic of the skulled vertebrates. Whether organs of smell exist in any worms or not is unknown; there are certain pits in some worms which may possibly be adapted for detecting odors. In some insects, at least, the organs of smell are without doubt well developed; the antenne of the burying beetles are large and knob-like, and evidently adapted for the detection of carrion. It is possible that certain organs situated at the base of the wings of the flies, and on the caudal appendages of the cockroach and certain flies, are of use in detecting odors. ANIMAL PSYCHOLOGY. We have seen that animals have organs of sense, of perception, in many cases nearly as highly developed as in man, and that in the Mammalia the eyes, ears, organs of smell and touch differ but slightly from those of our own species; also that the brain and nervous system of the higher mammals closely approximate to those of man. We know that all animals are endowed with sufficient intelligence to meet the ordinary exigencies of life, and that some insects, birds, and mammals are able, on occasion, to meet extraordinary emergencies in their daily lives. These facts tend to prove that all animals, from the lowest to the highest, possess, besides sensations, certain faculties which by general consent naturalists call mental, because they seem to be of 2 kind, however different in degree, with the mental manifestations of man. Besides in many if not most highly organized animals, sensations give rise to emotions, and in the higher animals, as well as man, the latter give rise to thoughts. The study of mental phenomena is the science of psychology. The study of the sensations and instincts, as well. as reasoning powers, of animals, is called animal psychology. The materials for the study of animal psychology are derived from the observations of the actions of animals; we do not, so to speak, know what is going on in their minds ; we draw our conclusions, as to whether an animal thinks or reasons, by studying our own mental processes. The study of human psychology is a most difficult one: one XXxii THE ANIMAL KINGDOM. man cannot read other men’s minds; he judges of their mental processes by their actions and his own mental processes. In the same manner we conclude that animals reason by judging of their acts alone. If human psychology is an inexact science, much more so is comparative psychology, which includes human as well as animal psychology. Although the Ameba performs operations which are akin to the instinctive acts of higher animals, it may in general be said that the nervous system is the organ of mind; not the brain alone, in animals which have a brain, but the entire nervous system. The mental manifestations of animals are not alone physiological, 7. e. auto- matic and reflex, but there are, at least in highly organized animals, such as crabs, insects, spiders, and vertebrates, processes which are psychological as opposed to physiological. The elementary or root principle of mind, as distinguished from purely physio- logical processes, is the power of making a choice between two alternatives presented to the animal. As we have said on another occasion, granted that insects have sensibilities, how are we to prove that they have an intellect? Simply by observing whether they make a choice between two acts. “On entering a closet, ants unhesitatingly direct their steps to the sugar-bowl in preference to the flour-barrel ; one sand-wasp prefers beetle- grubs to caterpillars, to store up as food for her young. In short, insects exercise discrimination, and this is the simplest of intellectual acts. They try this or that method of attaining an object. In fact, an insect’s life is filled out with a round of trials and failures.” While no one would doubt that an insect has the power of choice or discrimination, may this also be said of the lowest organisms, such as the Ameeba? Mr. Romanes believes that it can. “Ameba is able to distinguish between nutritious and non- nutritious particles, and in correspondence with this one act of discrimination it is able to perform one act of adjustment; it is able to enclose and to digest the nutri- tious particles, while it rejects the non-nutritious.” Some protoplasmic and unicellular organisms are able also to distinguish between light and darkness, and to adapt their movements to seek the one and shun the other; Mr. H. J. Carter thinks that the beginnings of instinct are to be found so low down in the scale as the Rhizopoda. As quoted by Romanes in his Animal Intelligence: “Even Athealiwm will confine itself to the water of the watch-glass in which it may be placed when away from saw- dust and chips of wood among which it has been living; but if the watch-glass be placed upon the saw-dust, it will very soon make its way over the side of the watch- glass and get to it.” Other facts are cited from Mr. Carter, upon which Mr. Romanes makes the following reflections : — “ With regard to these remarkable observations it can only, I think, be said that, although certainly very suggestive of something more than mechanical response to stimulation, they are not sufficiently so to justify us in ascribing to these lowest members of the zoological scale any rudiment of truly mental action. The subject, however, is here full of difficulty, and not the least so on account of the Amceba not only having no nervous system, but no observable organs of any kind; so that, although we may suppose that the adaptive movements described by Mr. Carter were non-mental, it still remains wonderful that these movements should be exhibited by such apparently unorganized creatures, seeing that as to the remoteness of the end attained, no less than the complex refinement of the stimulus to which their adaptive INTRODUCTION. XXxili response was due, the movements in question rival the most elaborate of non-mental adjustments elsewhere performed by the most highly organized of nervous systems.” It will be a matter of interest to trace the dawnings of mental processes in the lower animals. Having seen that something more than physiological effects are trace- able in certain acts of the protozoans; passing over the sponges, which are at best retrograde organisms, we come to the celenterates, especially the jelly-fishes. In none of these creatures have actions involving intelligence been observed; all their acts, so far as yet observed, are physiological, 7. e. reflex, the result of stimulation from without. Of the echinoderms, Romanes says: “ Some of the natural movements of these ani- mals, as also some of their movements under stimulation, are very suggestive of purpose ; but I have satisfied myself that there is no adequate evidence of the animals being able to profit by individual experience, and therefore, in accordance with our canon, that there is no adequate evidence of their exhibiting truly mental phenomena. On the other hand, the study of reflex action in these organisms is full of interest.” It is possible that the action of the earth-worm, a representative of the annelids, in drawing leaves down into its hole is “strongly indicative of instinctive action, if not of intelligent purpose — seeing that they always lay hold of the part of the leaf (even though an exotic one) by the traction of which the leaf will offer least resistance to being drawn down.” To the foregoing statement of Romanes we may add Darwin’s testimony as to the mental powers of the earth-worm, from his work entitled The Formation of Vegetable Mould through the Action of Worms. “Worms are poorly provided with sense-organs, for they cannot be said to see, although they can just distinguish between light and darkness; they are completely - deaf, and have only a feeble power of smell ; the sense of touch alone is well developed. They can, therefore, learn little about the outside world, and it is surprising that they should exhibit some skill in lining their burrows with their castings and with leaves, and, in the case of some species, in piling up their castings into tower-like constructions. But it is far more surprising that they should apparently exhibit some degree of intel- ligence instead of a mere blind instinctive impulse, in their manner of plugging up the mouths of their burrows. They act in nearly the same manner as would a man, who had to close a cylindrical tube with different kinds of leaves, petioles, triangles of paper, etc., for they commonly seize such objects by their pointed ends. But with thin ob- jects a certain number are drawn in by their broader ends. They do not act in the same unvarying manner in all cases, as do most of the lower animals ; for instance, they do not drag in leaves by their foot-stalks, unless the basal part of the blade is as nar- row as the apex, or narrower than it.” The next great type of animals is the molluscs. In many respects the higher worms, especially the annelids, are more highly organized than the clam, a snail, or cuttle-fish. The functions of sensation and locomotion are often in molluscs subordi- nate to the merely vegetative, such as feeding, nutrition, and reproduction. We should not, as Romanes has said, expect that molluscs would present any considerable degree of intelligence. “Nevertheless, in the only division of the group which has sense organs and powers of locomotion highly developed — viz., the Cephalopoda — we meet with large cephalic ganglia, and, it would appear, with no small development of intelligence.” Beginning with one of the lowest molluscs, the oyster, Romanes quotes from Mr. Darwin’s MS, as follows: “Even the headless oyster seems to profit from experience, XXXiV THE .ANIMAL KINGDOM. for Dicquemase asserts that oysters taken from a depth never uncovered by the sea, open their shells, lose the water within, and perish; but oysters taken from the same place and depth, if kept in reservoirs, where they are occasionally left uncovered for a short time, and are otherwise incommoded, learn to keep their shells shut, and they live for a much longer time when taken out of the water.” Is this act simply reflex? Limpets have been known, after making excursions from their resting places in order to browse on seaweed, to return repeatedly to one spot or home. The precise memory of direction and locality implied by this fact, adds Romanes, “seems to justify us in regarding these actions of the animal as of a nature unquestionably intelligent.” Concerning snails Darwin remarks: “These animals appear also susceptible of some degree of permanent attachment ; an accurate observer, Mr. Lonsdale, informs me that he placed a pair of land-shells (Helix pomatia), one of which was weakly, in a small and ill-provided garden. After a short time the strong and healthy individual disap- peared, and was traced by its track of slime over a wall into an adjoining well-stocked garden. Mr. Lonsdale concluded that it had deserted its sickly mate ; but after an ab- sence of twenty-four hours it returned, and apparently communicated the result of its successful exploration, for both then started along the same track and disappeared over the wall.” Mr. W. H. Dall gives a remarkable instance of intelligence in a snail, kept as a pet by a child, which recognized her voice and distinguished it from that of others. The lady who told the story to the person who sent it to Mr. Dall, after stating that her sister Georgie was, from the age of three years, quite an invalid, and remarkable for her power of putting herself en rapport with all living things, said: “ Before she could say more than a few words, she had formed an acquaintance with a toad, which used to come from behind the log where it lived, and sit winking before her in answer to her call, and waddle back when she grew tired and told it to go away. When she was between five and six years of age, I found a snail shell, as I thought, which I gave to her to amuse her, on my return from a picnic. The snail soon crawled out, to her delight, and after night disappeared, causing great lamentation. A large, old fashioned sofa in the front hall was moved in a day or two, and in it was found the snail glued fast ; it had crawled down stairs. I took a plant jar of violets and, placing the snail in it, carried it to her, and sunk a small toy cup even with the soil, filling it with meal. This was because I had read that French people feed snails on meal. The creature soon found it, and we observed it with interest for a while, as we found it had a mouth which looked :pink in- side and appeared to us to have tiny teeth also. We grew tired of it, but Georgie’s interest never flagged, and she surprised me one day by telling us that her snail knew her and would come to her when she talked to it, but would withdraw into its shell if anyone else spoke. This was really so, as I saw her prove to one and another time after time.” Mr. Dall adds: “An observer who noticed and remembered the pink buccal mass, the lingual teeth, and the translucent mistletoe-berry-like eggs, and after such an interval of time could so accurately describe them, is entitled to the fullest credence in other details of the story, and I have no doubt of its substantial accuracy, in spite of its surprising nature.” The Crustacea are perhaps, as regards intelligence, on a level with the majority of insects, excepting the white ants and ichneumons, wasps, and bees. The power of finding their way home, which of course is due to memory, is illus- trated in the following instance published by Mr. E. W. Cox in “Nature” for April 3, 1873. “The fishermen of Falmouth catch their crabs off the Lizard rocks, and they INTRODUCTION. XXXV are brought into the harbor at Falmouth alive and impounded in a box for sale, and the shells are branded with marks by which every man knows his own fish. The place where the box is sunk is four miles from the entrance to the harbor, and that is ‘above seven miles from the place where they are caught. One of these boxes was broken; the branded crabs escaped, and two or three days afterwards they were again caught by the fisherman at the Lizard rocks. They had been carried to Fal- mouth in a boat. To regain their home they had first to find their way to the mouth of the harbor, and when there, how did they know whether to steer to the right or to the left, and to travel seven miles to their native rocks?” It is scarcely possible to regard such an instance of what has been called the ‘homing instinct,’ as a purely physiological, reflex act, nor to consider the crab a mere automaton. Mr. Darwin, in his Descent of Man, refers to the curious instinctive habits of the large shore-crab (Birgus latro), which feeds on fallen cocoa-nuts, “by tearing off the husks fibre by fibre; and it always begins at that end where the three eye-like depres- sions are situated. It then breaks through one of these eyes by hammering with its heavy front pincers, and, turning round, extracts the albuminous core with its narrow ‘posterior pincers.” Little is really known of the instincts and_other intellectual traits of the crusta- ceans — but when we come to the insects the literature is very extensive, thanks to the observations of Reaumur, Bonnet, De Geer, Wyman, Bates, Belt, Miller, Moggridge, Lincecum, McCook, Sir John Lubbock, and others. As we have stated in our Half Hours with Insects: “Those who observe the ways of insects have noticed their extreme sensitiveness to external impressions; that their motions are ordinarily rapid and nervous. Look at the ichneumon fly as it alights on a leaf near a caterpillar: with what rapid motions it walks and flies about ; how swiftly its feelers vibrate ; how briskly it walks up and down surveying its victim. Look at a -mud wasp as it alights near a pool of water to moisten its mouth. How nervous are its motions, how nimbly it flies and runs about the edge of the water. The ant isa busy, active, dapper little creature, a nervous brusqueness pervading its movements. How susceptible insects are to the light may be tested on a damp, dark night by open- ing the windows. In dart a legion of insects of all sorts, each with a different mode of entrance, some beetle boldly flying about the room in its blundering noisy flight, or a Clisiocampa moth enters with a bound, and a series of somersaults over the table, like the entrée of a popular clown into the ring of a circus, though the latter may have the most self-possession of the two. “ Insects are, like most animals, extremely sensitive to electrical phenomena. Just before a thunder shower they are particularly restless, flying about in great numbers and without any apparent object. The appendages of insects, their feelers and their legs, must be provided with exquisitely sensitive organs to enable them to receive im- pressions from without. Everybody knows that insects have acute powers of sight. That they also hear acutely is a matter of frequent observation. Often in walking through dry bushes, the noise of one’s feet, in crushing through the undergrowth, starts up hosts of moths, disturbed in their noonday repose. If insects did not hear acutely, why should the Cicada have such a shrill cry? For whose ears is the song of the cricket designed unless for those of some other cricket? All the songs, the cries, and hum of in- sect life have their purpose in nature and are useless unless they warn off or attract some other insect. “ We know with a good degree of certainty that some insects have an acute sense XXXvi THE ANIMAL KINGDOM. of smell. The carrion beetles scent their booty afar off; the ants, the moths, all the insects attracted to flowers by the smell of the honey in them, evidently have well de- veloped organs of smell.” The internal structure of the brain of the ant, the bee, as well as the locust and other insects has been found to be unexpectedly complex, when compared with that of the higher worms and even the higher Crustacea, such as the lobster and cray fish. The brain of insects is a much more complicated organ than any of the succeeding ganglia, consisting more exclusively of sensory cells and nervous threads than any succeeding ones, though the subeesophageal one is also complex, consisting of sensory as well as motor ganglia, since this ganglion sends off nerves of special sense to the organs of taste and smell situated in the mouth-appendages. The third thoracic ganglion is also, without doubt, a complex one, as, in the locusts, the auditory nerves pass from it to the ears, which are situated at the base of the abdomen. But in the green grasshoppers, such as the katydids and their allies, whose ears are situated in their fore legs, the first thoracic ganglion is a complex one. In the cockroach and in Leptis (Chrysopila), a common fly, the caudal appendages bear what are probably olfactory organs, and as these parts are undoubtedly supplied from the last abdominal ganglion, this is proba- bly composed of sensory and motor ganglion-cells; so that we have in the ganglionated cord of insects a series of brains, as it were, running from head to tail, and thus in a still stronger sense than in Vertebrates the entire nervous system, and not the brain alone, is the organ of the mind of the insect. To briefly describe the brain of the locust, an insect not high in the scale, it is a double ganglion, but structurally entirely different from, and far more complicated than, the other ganglia of the nervous system. The cerebral lobes possess a ‘central body,’ and in each hemisphere is a ‘mushroom body ;’ besides the main cerebral lobes, the brain has also a pair of optic lobes and optic ganglia, and olfactory or antennal lobes, and these lobes have their connecting and commissural nerve-fibres, not found in the other ganglia. The locust’s brain appears to be as highly developed as that of the majority of in- sects, but that of the ant and the bee is more complicated than in other winged insects, owing to the much greater complexity of the folds of the calices or disk-like bodies capping the double stalk of the mushroom body. Now the ants, wasps, and bees are pre-eminently social animals, and we see by the structure of the brain why, in point of intelligence, they may exceed in mental development even the fishes, rep- tiles, and other lower vertebrates, and almost rival the birds in instinctive and rational acts. Experiments and anecdotes bearing upon the intelligence of ants, have been widely circulated in the works of Lincecum, McCook, Lubbock, Darwin, and Romanes, space not allowing us to reproduce them. Ants have the sense of sight and of scent and taste well developed, but the sense of hearing is feeble, sounds of various kinds not producing any effect upon them: their antennz are not, then, as in some insects, organs of hearing or smell, but have a delicate sense of touch, and, indeed, are the most important of sense organs to them. The sense of direction, the power of memory, are highly developed, and they perhaps are not destitute of the tenderer emotions, individuals being known to display sympathy for their wounded compan- ions or healthy friends in distress. Ants also have the power of communicating with one another, and they are susceptible of education. The young ant is led about the nest and “trained to a knowledge of domestic duties, especially in the care of the - INTRODUCTION. XXXvii larve ; they are also taught to distinguish between friends and foes.” When an ant’s nest is attacked by foreign ants, the young ones never join in the fight, but confine themselves to removing the pup; and Forel has by experiment proved that the knowledge of hereditary enemies is not wholly instinctive in ants. Moreover, besides carrying on the complicated duties of the formicary, ants add to their labors by keeping in their nests milch cows, as the Aphides substantially are; they also carry on slave-catching wars, and keep slaves generation after generation, with the same results of enfeebling and deteriorating the body and mind of the mas- ters, as has been experienced in human life. Ants also keep pets, and, to go to another extreme, carry on wars of conquest, rapine, and plunder. A few human races are said not to bury their dead: if this be so they are inferior to ants, whose care in disposing of the bodies of their dead has attracted the notice of Sir John Lubbock; and that they actually in some cases bury their dead was claimed by Pliny, and substantiated by recent observers, according to Romanes. And then we have the leaf-cutting ants, harvesting ants, honey-making ants, military ants, ants which bridge streams, dig wells, and tunnel under broad rivers. Wasps and bees can see much better than ants; indeed, they are far more depen- dent than the latter on the power of perceiving flowers, they also have a highly developed sense of direction, powers of communication, while the combined instinc- tive and reasoning powers they exhibit in making their nests, and in providing for or caring for their young are proverbial. Whether the instinct of building hexagonal cells is purely automatic or not has been disputed, but now it is conceded by Darwin, Romanes, and others that the process is not a purely mechanical one, but is “ constantly under the control of intelligent purpose ;” in other words, the worker bee knows what. it is about, is a conscious agent. Spiders also, though their nervous system is much less complicated than that of ants and bees, as well as insects in general, being built upon a different plan, show the most astonishing intellectual powers, particularly in spinning their webs; while as examples of special instincts the result of reasoning processes, at least in the beginning, are the acts of the water spiders, and especially the trap-door spiders. Spiders also, like ants and bees, are able to distinguish between persons, approach- ing those they know to be friendly, and shunning strangers. It is well known that spiders can be tamed, and there are well-authenticated anecdotes testifying to the high degree of intelligence of these creatures. Passing now to the branch of vertebrates, we do not find a sudden rise in the intellectual scale from bees to fishes, but that in reality fishes and reptiles are not so highly endowed mentally as the most highly organized insects. As Romanes truly says: “ Neither in its instincts nor in general intelligence can any fish be compared with an ant or bee, —a fact which shows how slightly a psychological classification of animals depends upon zoological affinity, or even morphological organization.” Fishes, he states, “display emotions of fear, pugnacity; social, sexual, and parental feelings; anger, jealousy, play, and curiosity. So far, the class of emotions is the same as that with which we have met in ants, and corresponds with that which is dis- tinctive of the psychology of a child about four months old.” Of batrachians, frogs and toads have more or less definite ideas of locality, while they will learn to recognize the human voice and come when called. The general intelligence of reptiles is higher than that of fishes and batrachians, but low compared with that of birds. Snakes and tortoises are said to be able to distinguish persons; XXXViil THE ANIMAL KINGDOM. and snakes, when tamed, exhibit some degree of affection for their master or mistress; while cobras may not only be tamed but domesticated. Between the lower vertebrates and the birds and mammals there is a wide intellec- tual gulf. In birds, the reasoning as opposed to the simply instinctive acts are mumerous. Birds are active, volatile, hot-blooded creatures, all their senses acute, and their cerebral hemispheres are far better developed than in the lower classes. To illustrate the high degree of intelligence of birds, we will state some of the con- clusions given by Romanes, referring the reader to his interesting work on Animal Intelligence for the anecdotes supporting his generalizations. The memory of birds for localities is well illustrated by their migratory habit of returning year after year to the same breeding-place. Buckland gives an account of a pigeon which remem- bered the voice of its mistress after an absence of eighteen months. Wilson relates an instance where a tame crow, after an absence of about eleven months, recog- nized his master. Parrots, which are perhaps the most intelligent of birds, sometimes chatter their phrases in their dreams, and “this shows a striking similarity of psychi- cal processes in the operations of memory with those which occur in ourselves.” Parrots have the power of, association of ideas, and they not only remember, but recollect ; “that is to say, they know when there is a missing link in a train of asso- ciation, and purposely endeavor to pick it up.” Among the emotions, birds for the first time show unmistakable feelings of affec- tion and sympathy. The loves of birds, the pining for an absent mate, and the con- jugal affection of doves, etc., proves that in them the simple sexual feelings are heightened and enhanced by the intellect. Their jealousy is proverbial, as seen in the singing birds; they also show emulation and resentment as well as vindictiveness ; their curiosity — the signs of a quick intellect —is highly developed; they have zsthetic emotions, love of bright-colored objects shown by the bower-bird, which builds its bowers at sporting-places in which the sexes meet, and where the males display their finery. Moreover, the singing birds, which stand at the head of the avian series, show a decided fondness for the music of their mates, aside from any utilitarian or sexual motives. Canaries, parrots, and doves are well known to take delight in human vocal or instrumental music. The nesting habits of birds call out our admiration not only for their wonderful architectural traits, but for the signs they exhibit of a plastic instinct, where reason teaches them to modify their nests in situation and form to adapt them to new condi- tions. In Montana and Colorado the wild goose builds in trees; the cuckoo occa- sionally lays her eggs on the bare ground, sits on them, and feeds her young; the falcon, which usually builds on cliffs, has been known to lay its eggs on the ground in a marsh; the house-swallow in the United States has changed its nesting habits since the country was settled and houses were built. The nests of young birds, as first noticed by Wilson, are distinctly inferior to those of older ones, both in situation and construction. “As we have here independent testimony of two good observers to. a fact which in itself is not improbable, I think we may conclude that the nest-making instinct admits of being supplemented, at any rate in some birds, by the experience and intelligence of the individual. M. Pouchet has also recorded that he has found a decided improvement to have taken place in the nests of the swallows at Rouen during his own lifetime; and this accords with the anticipation of Leroy, that if our observations extended over a sufficient length of time, and in a manner sufficiently close, we should find that the accumulation of intelligent improvements by individuals INTRODUCTION. XXXix of successive generations would begin to tell upon the inherited instinct, so that all the nests in a given locality would attain to a higher grade of excellence. Leroy also states that, when swallows are hatched out too late to migrate with the older birds, the instinct of migration is not sufficiently imperative to induce them to undertake the journey by themselves. They perish the victims of their ignorance, and of the tardy birth which made them unable to follow their parents.” Among the higher mammals are the true domestic animals, the friends of man, who are capable of education and of transmitting striking hereditary traits. Among the Educabilia we find the horse, dog, pig, ox, sheep, lama, dog, cat. Romanes insists that the horse is not so intelligent an animal as any of the larger Carnivora, while among her- bivorous quadrupeds his sagacity is greatly exceeded by that of the elephant, and in a lesser degree by that of his congener the ass. We question whether any one wha has seen Bartholomew’s “ Equine Paradox,” the twelve trained horses, will not place their intelligence at least as high as that of the pig. Pigs exhibit a degree of intelli- gence which “falls short only of that of the most intelligent Carnivora.” Romanes claims that the tricks taught the so-called “learned pig” would alone suffice to show this; “while the marvellous skill with which swine sometimes open latches and fasten- ings of gates, etc., is only equalled by that of the cat.” Among the Carnivora in a wild state, bears claim a high place in the psycholog- ical scale; the most astonishing anecdote is one published in “Nature” since the appearance of Mr. Romanes’ book. The story relates to a Russian bear. “The carcass of a cow was laid out in the woods to attract the wolves, and a spring trap was set. Next morning the forester found there the track of a bear instead of a wolf on the snow; the trap was thrown to some distance. Evidently the bear had put his paw in the trap and had managed to jerk it off. The next night the forester hid himself within shot of the carcass, to watch for the bear. The bear came, but first pulled down a stack of firewood cut into seven-foot lengths, selected a piece to his mind, and, taking it up in his arms, walked on his hind legs to the carcass. He then beat about in the snow all round the carcass with the log of wood before he began his meal. The forester put a ball in his head, which I almost regret, as such a sensible brute deserved to live.” Of the rodents, the majority, as the guinea-pig, hare, rabbit, etc., are low in intelli- gence; the squirrels have however some striking instincts, while the house rat, per- haps as the result of generations of persecution by man, has shown much intelli- gence; but the reasoning powers exhibited by the beaver are not only exceptional among rodents, but unique among dumb animals. In his admirable book on the beaver, the late Mr. Lewis H. Morgan thus speaks regarding what he calls the free intelligence of this animal: “The works of the beaver afford many interesting illus- trations of his intelligence and reasoning capacity. Felling a tree to get at its branches involves a series of considerations of a striking character. A beaver seeing a birch tree full of spreading branches, which to his longing eyes seemed quite desirable, may be supposed to say within himself: ‘If I cut this tree through with my teeth it will fall, and then I can secure its limbs for my winter subsistence.’ But it is necessary that he should carry his thinking beyond this stage, and ascertain whether it is sufficiently near to his pond, or to some canal connected therewith, to enable him to transport the limbs, when cut into lengths, to the vicinity of his lodge. A failure to cover these contingencies would involve him in a loss of his labor. The several arts here described have been performed by beavers over and over again. xl THE.ANIMAL KINGDOM. They involve as well as prove a series of reasoning processes undistinguishable from similar processes of reasoning performed by the human mind. “ Again, the construction of a canal from the pond, across the lowlands to the rising ground upon which the hard wood is found, to provide a way for the transportation of this wood by water, is another remarkable act of animal intelligence. A canal is not absolutely necessary to beavers any more than such a work is to mankind ; but it comes to both alike as the progress in knowledge. A beaver canal could only be con- ceived by a lengthy and even complicated process of reasoning. After the concep- tion had been developed and executed in one place, the selection of a line for a canal in another would involve several distinct considerations, such as the character of the ground to be excavated, its surface elevation above the level of the pond, and the supply of hard wood near its necessary terminus. These, together with many other ele- ments of fitness, must be ascertained to concur before the work could. be safely entered upon. When acomparison of a large number of these beaver canals has demonstrated that they were skilfully and judiciously located, the inference seems to be unavoidable that the advantages named were previously ascertained. This would require an exercise of reason in the ordinary acceptation of the term. “ And this leads to another suggestion. Upon the upper Missouri these canals are impossible from the height of the river-banks; and besides this they are unnecessary, as the cotton-wood, which is the prevailing tree, is found at the edge of the river. While, therefore, canals are unknown to the Missouri beavers, they are constantly in use among the beavers of Lake Superior. On the other hand, the ‘ beaver slides’ so common and so necessary on the upper Missouri are unnecessary, and therefore unknown, in the Lake Superior region. Contrary to the common opinion, is there not evidence of a progress in knowledge to be found in the beaver canal and the beaver slide? There was a time, undoubtedly, when the canal first came into use, and a time, consequently, when it was entirely unknown. Its first introduction was an act of progress from a lower to a higher artificial state of life. The use of the slide tends to show the possession of a free intelli- gence, by means of which they are enabled to adapt themselves to the circumstances by which they are surrounded. In like manner it has been seen that the lodge is not constructed upon an invariably typical plan, but adapted to the particular location in which it is placed. The lake, the island, and the bank lodge are all different from each other, and the difference consists in changes of form to meet the exigencies of the situation. These several artificial works show a capacity in the beaver to adapt his constructions to the particular conditions in which he finds himself placed. Whether or not they evince progress in knowledge, they at least show that the beaver follows, in these respects, the suggestions of a free intelligence.” The elephant is not only a most sagacious animal, but displays emotions of a high grade. Were the elephant bred in captivity, we might expect a still greater degree of intelligence, but it should be borne in mind that the individuals used as beasts of burden are hunted and tamed, and their intelligence dies with them. Romanes claims that “the higher mental faculties of the elephant are more advanced in their development than in any other animal, except the dog and monkey.” ‘Then comes the cat, whose intelligence is scarcely overrated by the popular judgment. Of all the cat stories we have read, the following one, copied from Romanes, caps the climax for the display of good judgment under trying circum- stances: while a paraffine lamp was being trimmed, some of the oil fell upon the back of the cat, and was afterwards ignited by a cinder falling upon it from the fire. “The INTRODUCTION. xli cat, with her back in a blaze, in an instant made for the door (which happened to be open) and sped up the street about one hundred yards, where she plunged into the vil- lage watering trough, and extinguished the flame. The trough had eight or nine inches of water in it and puss was in the habit of seeing the fire put out with water every night.” The dog is par excellence the friend of man, and without doubt his mind has been moulded as no other animal’s, by that of his master. “The intelligence of the dog,” says Romanes, “is of special, and, indeed, of unique interest, from an evolutionary point of view, in that from time out of record this animal has been domesticated on account of the high level of its natural intelligence; and by persistent contact with man, coupled with training and breeding, its natural intelligence has been greatly changed. In the result we see, not only a general modification in the way of depend- ent companionship and docility, so unlike the fierce and self-reliant disposition of all wild species of the genus; but also a number of special modifications, peculiar to certain breeds, which all have obvious reference to the requirements of man.” Dogs have long memories, and they are superior to all other animals in their highly devel- oped emotions. They can communicate simple ideas to one another as well as to their master, through the medium of a canine sign-language. Reaching the highest order of mammals, the Primates, we are confronted with what Romanes may be correct in supposing to be “a mental life of a distinctly differ- ent type from any that we have hitherto considered, and that in their psychology, as in their anatomy, these animals approach most nearly to Homo sapiens.” This, how- ever, is an open question, and it is held by some that other animals, as the dog, exceed the monkeys and apes in intelligence. We are not sure, however, but that the monkeys and apes would, if bred in domestication for successive generations, prove that their highly developed brains place them on a higher psychological level than the dog, cat, elephant, hare, or pig. ‘The orang,” says Romanes, “ which Cuvier had, used to draw a chair from one end to the other of a room, in order to stand upon it so as to reach a latch which it desired to open; and in this we have a display of rationally adaptive action which no dog has equalled, although . . . it has been closely approached. Again, - Rengger describes a monkey employing a stick wherewith to pry up the lid of a chest, which was too heavy for the animal to raise otherwise. This use of a lever as a mechan- ical instrument is an action to which no animal other than a monkey has ever been known to attain; and, as we shall subsequently see, my own observation has fully corroborated that of Rengger in this respect. More remarkable still, as we shall also subsequently see, the monkey to which J allude as having myself observed, succeeded also by methodical investigation, and without any assistance, in discovering for himself the mechanical principle of the screw; and that monkeys well understand how to use stones as hammers is a matter of common observation since Dampier and Wafer first described this action as practised by these animals in the breaking open of oyster-shells.” As regards the brains of apes, Bastian remarks: “In the conformation of their brain, the chimpanzee, the gorilla, and the orang approach, as we have seen, most closely to that of man; but it must never be forgotten that although in general shape, in the disposition of its fissures, and in the arrangement of its convolutions, as far as they go, there is this striking resemblance to the human brain, yet in actual size or weight, the brain of the man-like apes is widely separated from that of man. The heaviest brain belonging to one of these creatures, as yet examined, has been barely one half of the weight of the smallest normal human brains, although the weight of xlii THE ANIMAL KINGDOM. the entire body in the great gorilla may be nearly double that of an ordinary man. The brains of these three kinds of ‘ man-like’ apes differ considerably among them- selves ; as we have seen, each in some respects approaches nearer to that of man than the others, though on the whole it is considered that the brain of the orang is slightly higher in type than that of the other two.” Bastian also quotes, as follows, from David Hartley’s “Observations on Man” (1834): “It is remarkable that apes, whose bodies resemble the human body more than those of any other brute creature, and whose intellects also approach nearer to ours, — which last circumstance may, I suppose, have some connection with the first, — should likewise resemble us so much in the faculty of imitation. Their aptness in handling is plainly the result of the shape and make of their fore legs and their intel- lects together, as in us. Their peculiar chattering may perhaps be some attempt towards speech, to which they cannot attain, partly from the defect in the organs, partly, and that chiefly, from the narrowness of their memories, apprehensions, and associations.” We will close this too rapid view of the supposed facts in animal psychology by quoting from Bastian the following anecdote from Leuret: “One of the orangs, which recently died at the menagerie of the Musée, was accustomed, when the dinner hour had come, to open the door of the room where he took his meals in company with several persons. As he was not sufficiently tall to reach as far as the key of the door, he hung on to a rope, balanced himself, and, after a few oscillations, very quickly reached the key. His keeper, who was rather worried by so much exactitude, one day took occasion to make three knots in the rope, which, having thus been made too short, no longer permitted the orang-utan to seize the key. The animal, after an ineffectual attempt, recognizing the nature of the obstacle which opposed his desire, climbed up the rope, placed himself above the knots, and untied all three, in the presence of M. Geof- frey Saint-Hilaire, who related the fact to me. The same ape wishing to open a door, his keeper gave him a bunch of fifteen keys; the ape tried them, in turn, till he had found the one which he wanted. Another time a bar of iron was put into his hands, ’ and he made use of it as a lever.” Let us now look at the inductions which may be drawn from the facts now known regarding the intelligence of animals. It is evident that animals are not mere physi- ological machines. We may, with Romanes, reject the view of Descartes, Huxley, and others, that animals are merely automata, on the ground that it can never be accepted by common sense, while “ by no feat of logic is it possible to make the theory apply to animals to the exclusion of man.” , We discern in the mental traits of animals, besides reflex acts, those which are in- stinctive and those which are the result of reasoning processes. The following defi- nitions, by Mr. Romanes, will answer well our purpose: “Reflex action is non-mental neuro-muscular adjustment, due to the inherited mechanism of the nervous system, which is found to respond to particular and often recurring stimuli, by giving rise to particular movements of an adaptive, though not of an intentional kind. “Jnstinct is reflex action into which there is imported the element of conscious- ness. The term is therefore a generic one, comprising all those faculties of mind which are concerned in conscious and adaptive action, antecedent to individual expe- rience, without necessary knowledge of the relation between means employed and ends attained, but similarly performed under similar and frequently recurring circumstances by all the individuals of the same species. INTRODUCTION. xiii “ Reason, or intelligence, is the faculty which is concerned in the intentional adap- tation of means to ends. It therefore implies the conscious knowledge of the relation between means employed and ends attained, and may be exercised in adaptation to circumstances novel alike to the experience of the individual and to that of the species.” It would appear, then, that animals have, in some slight degree, what we call mind, with its threefold divisions of the sensibilities, intellect, and will. When we study animals in a state of domestication, especially the dog or horse, we know that they are capable of some degree of education, and that they transmit the new traits or habits which they have been taught to their offspring; so that what in the parents were newly acquired habits become in the descendants instinctive acts. We are thus led to suppose that the terse definition of instinct, by Murphy, that it is ‘the sum of inherited habits,’ is in accordance with observed facts. Indeed, if animals have sufficient intelligence to meet the extraordinary emergencies of their lives, their daily so-called instinctive acts, requiring a minimum expenditure of mental energy, may have originated in previous generations; and this suggests that the instincts of the present generation may be the sum total of the inherited mental experiences of former generations. Descartes believed that animals were automata. Lamarck expressed the opinion that instincts were due to certain inherent inclinations arising from habits impressed upon the organs of the animals concerned in producing them. Darwin does not attempt any definition of instinct; but he suggests that ‘several distinct mental actions are commonly embraced by this term,’ and adds that ‘a little dose, as Pierre Huber expresses it, of judgment or reason often comes into play, even in animals low in the scale of nature.’ He indicates the points of resemblance be- tween instincts and habits, shows that habitual action may become inherited, especially in animals under domestication; and since habitual action does sometimes become inherited, he thinks it follows that “the resemblance between what originally was a habit and an instinct becomes so close as not to be distinguished.” He concludes that, by natural selection, slight modifications of instinct which are in any way use- ful accumulate, and thus animals have slowly and gradually, “as small consequences of one general law,” acquired, through successive generations, their power of acting instinctively, and that they were not suddenly or specially endowed with instincts. Rev. J. J. Murphy, in his work entitled Habit and Intelligence, seems to regard instinct as the sum of inherited habits, remarking that “reason differs from instinct only in being conscious. Instinct is unconscious reason, and reason is conscious in- stinct.” This seems equivalent to saying that most of the instincts of the present generation of animals are unconscious automatism, but that in the beginning, in the ancestors of the present races, instincts were more plastic than now, such traits as were useful to the organism being preserved and crystallized, as it were, into the instinctive acts of their lives. This does not exclude the idea that animals, while in some respects automata, occasionally perform acts which transcend instinct; that they are still modified by circumstances, especially those species which in any way come in contact with man; are still in a degree free agents, and have unconsciously learned, by success or failure, to adapt themselves to new surroundings. This view is strength- ened by the fact that there is a marked degree of individuality among animals. Some individuals of the same species are much more intelligent than others; they act as leaders in different operations. Among dogs, horses, and other domestic animals, xliv THE ANIMAL KINGDOM. those of dull intellect are led or excelled by those of greater intelligence, and this indicates that they are not simple automata, but are also in a degree, or within their own sphere, free agents. REPRODUCTION AND EMBRYOLOGY. On a previous page, as an introduction to the subject of tissues, we discussed some of the earlier features of the development of animals, but now we need, in a brief manner, to consider the subject from another point of view, and, in a general way, to trace it out for the whole animal kingdom. As soon as the microscope was perfected and constantly used by morphologists as an instrument of exact research, a flood of light was thrown upon the subject of repro- duction. In its ultimate analysis reproduction essentially consists in the separation of a portion of an adult animal from itself, this portion developing into an animal like the parent. It was seen that in the one-celled animals this process was identical with cell division, and it was called fission. It was also found that, as in the Hydra and allied polyps, a bud would form, and develop into a Hydra, and finally separate from the original parent Hydra. Although in the first place the formation of the bud is due to cell-division, a single cell giving rise to the bud, this process is called budding or gemmation. It was likewise discovered that in those animals which produce eggs, the latter were fertilized by a very minute and greatly modified cell, called the sperm-cell, or spermatozoon. Now, in most of the many-celled animals there are two kinds of individuals, one female, which produces in its ovaries eggs, and the other the male, which produces in its testes the spermatozoa. Reproduction, or fertilization of the egg, in such animals, consists in the fusion of the sperm-cell with the nucleus of the egg; this is called sex- ual reproduction. From the moment of fertilization begins the life of the germ, which is called an embryo, while the history of the changes undergone by the embryo from the time of fertilization of the egg to maturity is called Embryology. As was said a few pages back, the egg is essentially a simple cell, and in its earlier condition it is not to be distinguished from the other cells of the reproductive organs, but with development it changes in many respects, prominent among which is an in- crease in size. The essential part of the egg is its protoplasm, but to this is usually added a varying quantity of a nutritive material, the deutoplasm or food-yolk. Besides, in most forms, protective envelopes, etc., are added. The most familiar egg, that of the barnyard fowl, is poorly adapted to give us an idea of the true nature of an egg. Here the protoplasm is very small in quantity, and forms but a small patch on one side of the ‘yolk,’ which is almost entirely protoplasm. Another adventitious substance is the ‘white,’ while the shell and the membranes are merely protective, and not essential features. In another respect this egg is unsuited for our purposes, for, at the time of laying, the segmentation has progressed to a considerable extent, and the egg is no longer to be regarded as a simple cell. The typical egg, then, is a mass of protoplasm, which is differentiated, as in any other cell, into nucleus and nucleolus, the latter in turn exhibiting a structure to be de- scribed below. In almost all eggs there is found one or more protective envelopes, which, according to the mode of origin, have received different names. When it is produced by the egg itself, it is called the vitelline membrane ; when by the ovarian tissues of the parent it receives the name chorion. These envelopes in many forms INTRODUCTION. xlv are perforated by one or more minute openings which serve for the passage into the egg of nutritive material from the parent, and for the introduction of water in aquatic forms. Besides, in many forms there is a larger opening, the micropyle, for the entrance of the spermatozoon which is to fertilize the egg. Recent investigations have shown that an egg or a cell is far from the simple structure which it was once imagined to be; the protoplasm of the cell is not a homo- geneous substance, while the nucleus or germinative vesicle is very complex. The latter is enveloped by a special membrane and filled with a protoplasm, in which floats a tan- gled network of fibres. | What is called the nucleolus is now regarded by Flemming and by Carnoy (two of the most profound students of cells) as a specialized portion or portions of the network. The nucleolus (there may be three or more in an egg) is called in the older works the germinative spot, or the Wagnerian vesicle, the latter name being applied in honor of its first discoverer. In the living egg the nucleolus is usually readily distinguished under the microscope by its great refrangibility, but to recognize the network it is necessary to employ stains and other reagents. This egg, as we have described it, undergoes an extensive and complicated series of changes (known as the maturation of the egg) before it is ready for impregnation, although it is to be noted that in some instances the maturation is concomitant with impregnation. These changes may be summarized as follows:— At first the nucleus occupies a position near (but rarely at) the centre of the egg ; it now moves to near the surface, where its membrane breaks down, and the filaments, etc., almost en- tirely disappear or at least lose their former character. In the place where the last remnants of the nucleus were seen, there now appears a spindle-shaped body made up of granules arranged in lines, while from either end other lines of granules are arranged in a radial manner. The whole presents an appearance closely similar to that seen when iron filings are exposed to the influence of a horse- shoe magnet, while from its resemblance to two stars joined it has received the name amphiaster. It may be observed Fic. VI.— Formation of polar in passing, that amphiasters are characteristic not only of Plobule,-n, nucleus: p, polar the maturation of the egg, but of cell division as well; eee 8, spindle shaped the connection between the two will appear in the sequel. The maturation spindle usually takes a position at nearly right angles to the surface of the egg, and soon from the outer end a prominence appears, extending out beyond the rest of the egg. The spindle now divides, and the prominence separates from the egg and forms what is known as a polar globule. Again the portion of the spindle which remains within the egg approaches the surface and a second polar globule is formed in the same manner as the first. | Now, the part of the spindle left in the egg assumes a nearly spherical condition, and sinks back into the egg, where it appears exactly like the original nucleus. It is called the female pronucleus. The meaning of these wonderful phenomena is far from evident. The best expla- nation as yet advanced, is that given by Balfour and Minot independently, which gains additional plausibility from the fact that essentially similar phenomena are seen in the formation of the male reproductive elements, the spermatozoa. In brief it is this: — All cells have inherited from their protozoan ancestors the elements of both sexes ; they are hermaphroditic, and the eggs and spermatozoa cells are the same. Be- fore they can unite it is necessary that each should get rid of the element to be sup- ‘plied by the other, and in this light the formation of the polar globules is to be viewed xlvi THE ANIMAL KINGDOM. as an elimination of the male portion from the egg, while, mutatis mutandis, the same may be said of the remnants of the mother-cells from which the spermatozoa are formed. Now the egg is ready for that union with the male element, or spermatozoa, which is called fertilization or impregnation. The process in most if not all forms is essentially as follows: One or more spermatozoa enter the egg; in some , cases it has been found that, if more than one entered, the re- sult was a malformation, to be noticed below; in other eggs, on the contrary, several spermatozoa are necessary for fertili- -s zation. As soon as the head of the spermatozoon enters the Hig Wii deenes olaaamine MOE it forms a clear space known as the male pronucleus. teneae Le a Around this radial striz appear, and it slowly travels toward J, female pronucleus; s,sper- the female pronucleus until the two unite. This compound structure, thus formed, is known as the segmentation nucleus. Now begins the segmentation which was de- scribed briefly on a preceding page, which results in the conversion of the egg into a mass of cells, and which need not be repeated here. One inter- esting fact, however, may be mentioned. Hermann Fol, in his studies on the development of the star- fish, found that, if several spermatozoa obtained entrance to the egg, a corresponding number of segmentation nuclei were formed; and although development proceeded but a short distance, the results of this abnormal condition were visible throughout. Each nucleus formed a centre of seg- mentation, and when the time arrived for the form- =H : i" Fic. Vill. — Abnormal astrulation in an ation of a gastrula, the same influence was felt, and, echinoderm, the result of multiple im- 2 7 pregnation. as shown in the adjacent cut, there were several invaginations. These observations possess a high interest from a teratological point of view, as they may afford an explanation of the formation of double monsters. — METAMORPHOSIS. After the formation of the germ layers as described on pages ix. to xii., the develop- ment of the various organs proceeds, for the details of which one should consult the accounts of the different groups in the body of this work, and especially Balfour's clas- sic Treatise on Comparative Embryology. Still we may consider here some of the questions connected with metamorphosis, This term, which has been employed for many years, is used to indicate the series of changes which an animal undergoes after being born or after hatching from the egg. In some cases the changes are very slight, the young leaving the egg in nearly the adult form, while in others, of which a famil- iar instance is furnished by the butterfly, the modifications which are introduced be- tween the egg and the mature condition are most startling. As other examples of these complete metamorphoses, we would refer the reader to the jelly-fish, star-fish, sea- urchins, worms, molluscs, insects, crustaceans, and batrachians, as described in the body of this work. One of the most curious is that presented by the larval form known as Actinotrocha, which converts itself into the mature worm Phoronis, by apparently turning itself inside out. Ifthe reader will compare different accounts; and notice that INTRODUCTION. xlvii in the same group, sometimes, as in the case of Balanoglossus, even in the same genus, one species will develop directly, while another has a complicated life history, he will be led to the inquiry, What is the meaning, what the use of this metamorphosis in one and not in the other? If one examines carefully the embryological changes of those forms hatched in the form of the adult, he will see that frequently they present, while in the egg, an epitome of the development of their relatives in which the changes have been much more marked. The question is largely one of nutrition, though many other conditions enter into the problem. In those forms where the food supply in the egg is abundant, the tendency is to simplify the development and to accelerate it. All superfluous features are consequently omitted, or are passed in a hasty manner. On the other hand, where the amount of food is small, the animal is forced to begin life for itself at an early date, and hence it needs every protection against the dangers of its environment. An interesting point to be noticed in this connection has recently been described by Mr. W. J. Sollas, in the development of the sponge, Halisarca. In the Mediterra- nean the embryos of this sponge escape from the tissues of the parent when they have arrived at the blastula condition, and they then swim about freely by means of the cilia clothing the surface; in the same species on the shores of the English Channel, the young are retained until after gastrulation and the formation of the canal system. According to Sollas the explanation of this difference is not difficult. In the Medi- terranean there are no strong currents, and it is evidently best for the parents to get rid of the young at as early a moment as possible, thus escaping a longer drain upon its energies. In the English Channel, on the other hand, the current is very strong, and were the embryos to be set free at the stage at which they are in the Mediterra- nean, the chances are that they would be swept away from proper places for their further development, and hence they are retained until nearly ready for attachment to the rocks. The same influences, nutrition and environment, affect other forms. Almost all crustaceans undergo a complicated metamorphosis, and in their various stages they lead very different lives. In the young they are usually free-swimming, and hence they need protection from aquatic foes. This is usually gained in two ways; by trans- parent tissues which render them invisible to fishes, and by the development of spines and processes from the body, which increases their size without materially adding to their weight, thus preventing their entrance to the mouths of the smaller forms. Still not all the Crustacea undergo these changes; in the whole group of tetradecapods no metamorphosis is known, while in the land-crabs of the tropics the young, when hatched, are closely similar to the parents. In this latter instance, where the adults live on the land, only going to the sea at the approach of the breeding season, it is easy to be seen why the development should be direct. In other cases the use of larval forms is very evident. Many forms, like the bar- nacles, sponges, and the oysters, lead a stationary life, but the young are free-swim- ming. This change in form and mode of life undoubtedly is of great benefit to the species, for if at a given moment the parents were swept out of existence, the young, living in a different station, would continue the species; and, besides, they serve to distribute the race from point to point. The foregoing paragraphs have reference to the larval forms, and the persistence and value, and the benefits of a metamorphosis. Some of these characters are engrafted on the primitive stock, while others are due to the origin, the evolution of the group, and xlviii THE ANIMAL KINGDOM. in all discussions the greatest care must be taken to discriminate between the ancestral and the adaptive features. We can best illustrate this by taking the case of the de- velopment of a mammal, and showing how in its various stages it presents a compen- dium of its history, When, in the mammalian germ, the nervous system and notochord arise, it is on a level with the larva of an Ascidian; with the formation of protovertebre, it represents the Amphioxus; a brain, and gill clefts and limbs, indicate a fish and amphibian stage; the development of an allantois and closure of the gill clefts places it on an avian plane; while with the appearance of a placenta the mam- malian features are assumed. These successive stages of the individual are closely paralleled by that of the class. The fleshy, boneless form of Amphioxus and the tunicates would not be preserved, but from fishes to man the sequence of remains in the rocks accords with that.derived from embryology. It must not be understood from this that the mammals have been derived from the birds. The true line of descent is far different, as will be explained on a subsequent page. It merely indicates that the mammal and the bird have arisen from a common stock, and have pursued the same course during a portion of their history. ALTERNATION OF GENERATIONS AND PARTHENOGENESIS. Having spoken of the normal method of development of animals, we may turn to certain unusual or abnormal modes of production. As an example of what is known as alternation of generations may be cited the history of the jelly-fish, such as the naked-eyed meduse (Melicertwm and Campanularia), which at one time of life develop by budding, at another by eggs; of the trematode worms, the adult forms of which lay eggs, while the redia or proscolex of the same worm produces cercarie by internal budding. Here also may be cited the cases of strobilation of Avrelia, the tape-worm, Wats, Syilis, and Autolytus, among annelids. Thus among ccelenterates and worms, as well as some Crustacea, a large number of individuals are produced, not from eggs, but by budding. Similar occurrences take place among insects, as the Apts or plant-louse, in which a virgin Aphis may bring forth in one season nine or ten generations of Aphides, so that one Aphis may become the parent of millions of young. These young directly develop from eggs or buds which are never fertilized, hence the term parthenogenesis, or virgin-reproduction, sometimes called agamogenesis (or birth without marriage). The bark-lice as well as the Aphides develop in this manner during the warm weather ; but at the approach of cold both male and female Aphides and Coccide appear, the females laying fertilized eggs, the first spring brood thus being produced in the nor- mal, usual manner. Still more like the production of young in the redia of the trematode worms is the case of the larva of a small gall-gnat (JMastor), which during the colder part of the year from autumn to spring produces a series of successive generations of larvee like itself, until in June the last brood develops into sexually mature flies, which lay fertilized eggs. While the larval Mfiastor produces young like itself, the pupa of another fly, Chironomus, also lays unfertilized eggs from which the flies arise. A number of moths, including the silk-worm moth, are known to lay unfertilized egos which produce caterpillars. Among the Hymenoptera, the currant saw-tfly, cer- tain gall-flies, several species of ants, wasps (Polistes), and the honey-bee, are known to produce fertile young from unfertilized eggs; in the case of the ants and bees, the INTRODUCTION. xlix workers lay eggs which result in the production of males, while the fertilized eggs laid by the female ant or queen bee produce females or workers. Taking all these cases together, parthenogenesis is seen to be due to budding, or cell-division or multiplication. Now it will be remembered that the egg develops into an animal by cell-division, so that fundamentally parthenogenesis is due to cell- division, the fundamental mode of growth; hence, normal growth and _partheno- genesis are but extremes of a single series. In this connection, it will be remembered that all the Protozoa reproduce by simple cell-division, that among them the sexes are differentiated, that they do not reproduce by fertilized eggs; hence, so to speak, among Protozoa, parthenogenesis is the normal mode of reproduction ; and when it exists in higher animals it may possibly be a survival of the usual protozoan means of stocking the world with unicellular organisms, with which we know the waters teem. And this leads us to the teleology or explanation of the cause why parthenogenesis has sur- vived here and there in the world of lower organizations; it is plainly, when we look at the millions of Aphides, of bark-lice, the hundreds of thousands inmates of ant- hills and bee-hives, for the purpose of bringing immediately into existence great numbers of individuals, thus ensuring the success in life of certain species exposed to great vicissitudes in the struggle for existence. That this unusual mode of reproduc- tion is all-important for the maintenance of the existence of most of the parasitic worms, is abundantly proved when we consider the strange events which make up the sum total of a fluke or tape-worm’s biography. Without this faculty of the compara- tively sudden production of large numbers of young by other than the slow, limited process of ovulation, the species would be stricken off the roll of animal life. Dimorruism anp PoLyMoRPHISM. Involving the production of young among many-celled animals (Metazoa) by what is fundamentally a budding process, we have two sorts of individuals. When the organism is high or specialized enough to lay eggs which must be fertilized, we have a differentiation of the animal into two sexes, male and female. Reproduction by bud- ding involves the differentiation of the animal form into three kinds of individuals — 7. é., males, females, and asexual individuals, among insects often called workers or neuters. These have usually, as in ants and bees, a distinct form, so as to be readily recognized at first sight. Among the Coelenterata and worms the forms repro- ducing by parthenogenesis are usually larval or immature, as if they were prematurely hurried into existence, and their reproductive organs had been elaborated in advance of other systems of organs, for the hasty, sudden production, so to speak, of large numbers of individuals like themselves. In insects, dimorphism is intimately connected with agamic reproduction. Thus the summer wingless, asexual Ap/is and the perfect winged autumnal Aphis may be called dimorphic forms. The perfect female may assume two forms, so much so as to be mistaken for two distinct species. Thus, an oak gall-fly (Cynips quercus-spongtfica) occurs in male and female broods in the spring, while the autumnal brood of females was described originally as a separate species under the name C. aciculata. Walsh considered the two sets of females as dimorphic forms, and that Cynips aciculata lays eggs which produce C. quercus-spongifica. Among butterflies, dimorphism occurs. Papilio memnon has two kinds of females, one being tailless, like the tailless male, while Papilio pammon is polymorphic, there being three kinds of females besides the male. , re | ] THE ANIMAL KINGDOM. There are also four forms of Papilio ajax, the three others being originally described as distinct species under the name of P. Marcellus, P. telamonides, and P. walshii. Our Papilio glaucus is now known to be a dark, dimorphic, climatic form of the common Papilio turnus. There are dimorphic males among certain beetles, as in the Golofa hastata of Mexico, in which one set of males are large and have a very large erect horn on the prothorax, and in the other the body is much smaller, with a very short conical horn. Temperature is also associated with the production of polymorphic forms in the temperate regions of the earth, as seen in certain butterflies, southern forms being varieties of northern forms, and alpine ‘species’ proving to be varieties or seasonal forms of lowland species. For example, Weismann states that the European butter- flies, Lycaon amyntas and polysperchon are respectively summer and spring broods. Anthocharis simplonica is an Alpine winter form of Anthocharis delia, as is Pieris bryonic of Pieris napi. In this country, as Edwards has shown, two of the poly- morphic forms of Papilio ajaw—i. ¢., walshit and telamonides— come from winter chrysalids, and P. Marcellus from a second brood of summer chrysalids. It thus appears that polymorphism is intimately connected with the origin of species. Per- haps the most remarkable case of polymorphism is to be seen in the white ants (Zer- mites), where in one genus there are two sorts of workers, two sorts of soldiers, and two kinds of males and females, making eight sorts of individuals ; in the other genera there are six. Among true ants there are, besides the ordinary males, females, and workers, large-headed workers. In the honey-ant (Myrmecocystus mexicanus), be- sides the usual workers, there are those with enormous abdomens filled with honey. Other insects, especially certain grasshoppers, are dimorphic. Certain parasitic nema- tode worms are dimorphic ; and among the celenterates, especially the hydroids, there is a strong tendency to polymorphism. EVOLUTION. In a single word — evolution—is comprised that vast complex of factors which has resulted in the stocking of our earth with plants and animals, each after its kind. The explanation of the process by which the life-forms of this planet have been brought into existence is an intricate series of problems within problems, as infinite as is the variety in nature itself. In early pre-scientific times, in the childhood of the race, it seemed sufficient to say that every living thing was created, and with this statement the majority of mankind were content to rest; not so, however, a few isolated thinkers, who, from the time of Democritus, have questioned nature, and as earnestly as reverently sought how these things could have come to pass. When geology began to assume a definite shape; when Cuvier and Lamarck had sketched out the leading types of animal life, as Jussieu did the earth’s flora; and after palaontology began to be a science, and it became known that the earth had been peopled by successive floras and faunas, appeared Lamarck and St. Hilaire as philosophers, who combated the cataclysmic ideas of Cuvier, and who maintained both the unity of organization of organic beings and the immense lapse of time since the beginning of life—time enough for the changes and adaptations needed to bring about the present condition of things. In 1802, twenty-three years before the appearance of Cuvier’s Discourse Sur les Révolutions du Globe, Lamarck uttered these striking words; “Pour la nature, le temps mest rien, et west jamais une difficulté ; elle la toujours a sa disposition, et INTRODUCTION. li cest pour elle un moyen sans bornes avec lequel elle fait les plus grandes choses comme les moindres.” In 1809 Lamarck published his Philosophie Zoologique. This work comprised the results of his speculations as well as of his special work of concise description, determination, and classification of vegetable and animal species. He was struck with the differences, but still more with the resemblances in animals; he noticed their variations, and, as Martins has said, a triple impression was made on his mind: the certainty of the variability of species under the influence of external agencies; that of the fundamental unity of the animal kingdom; finally, the probability of the successive generation of different classes of animals, arising, so to speak, one from another, like a tree whose branches, leaves, flowers, and fruits are the results of successive evolutions of a single organ, —the seed or bud. All this was however speculation, a priori, premature guesses without a broad basis of facts. The fulness of time had not yet come. The year 1809 was long ante- rior to the general use of the microscope, before the sciences of embryology, of his- tology, the doctrine of the cell, and before the principles of paleontology and zoo- geography had been founded. Lamarck was almost forgotten, his speculations had been treated with silent contempt or indifference. A period of over half a century succeeded, an age of busy search for facts, a period prolific in inductive sciences, —a sisterhood of knowledge as numerous as the family of Niobe. In the year 1859, Darwin, Wallace, Bates, and among botanists, Hooker, unanimously insisted on the fact of the variation of species and their origin by natural causes ; and they supported their views by special more or less limited theories. Darwin’s theory of natural selec- tion was adopted with a rapidity and unanimity unparalleled in the history of science. We will now examine the general argument, and state some of the general principles upon which the modern scientific theory of descent is based. There are three laws or inductions supporting the theory: 1. Change in the envi- ronment of the organism, involving adaptation to such change. 2. Transmission by heredity of ancestral together with acquired traits. 3. The selection of useful traits and their preservation and fixity. Around each of these leading principles cluster others accessory and indispensable, and doubtless still others may yet be discovered. The recognition of two factors have attracted fresh attention to the theory of descent, and caused it to be generally accepted as a working theory indispensable to biological science; these are (1) the facts of variation with the difficulty of limiting species and genera, and the discovery of connecting links between the higher groups of animals, including orders, classes, and sub-kingdoms ; and (2) the influence on the plant or animal of a change in the environment. The second of these factors was advocated by Lamarck and St. Hilaire. Since the publication of Darwin’s special theory of natural selection, which was accepted as a vera causa by the large propor- tion of naturalists, a few have not been satisfied with this theory alone, but have in various directions gone back of Darwin and natural selection to views like those of Lamarck, whether they were acquainted with his theory and works or not. Darwin took the tendency to variation as the foundation upon which to erect the superstruc- ture of natural selection; others have sought to account first for the tendency to varia- tion, and then given natural selection its due place as a secondary, though important, phase. Had Lamarck, with his unquestioned ability as a thinker and observer, lived at the present time, when so many new sciences have arisen, and the older ones of chem- istry and physics have been revolutionized, he would have checked his imagination li THE ANIMAL KINGDOM. here and there, and given us a theory well grounded on facts. It was reserved, how- ever, for the tireless genius of Darwin, with his masterly handling of facts, to impress his conclusions on the age, supporting them as he did with an overwhelming array of facts. His compactly built superstructure was erected on a temporary foundation, which it will be the work of the future to rebuild with solid masonry, resulting from cen- turies of labor in the field first pointed out by Lamarck. The influence of Lamarck’s work was feeble, owing to the strong counter-currents set up by Cuvier, Agassiz, and popular prejudice. What Lamarck actually accomplished has been restated by Charles Martins. He noticed the variations of species, both of animals and plants. The best results of his labors of over thirty years in botany, and afterwards of thirty years in zoology, were his division of the animal kingdom into vertebrates and invertebrates; his founding the classes of Infusoria and of Arachnida; his separation of the Cirripedia from the Mollusca, only a few years before Thompson discovered their true affinities. Lamarck had a powerful imagination, and was a born speculator; but the age in which he worked was barren of facts, and many of his theories were ill-founded. The grand results of his work were clear views as to the unity of organization of the animal kingdom, the filiation of all animal forms, and the influence of external agencies on the varia- tion of species; he recognized the effects of use and disuse on the development and atrophy of organs; he recognized the agency of the water, of air, of light, of heat, in bringing about changes in organisms; finally, Lamarck was the first to construct a phylogeny or genealogical tree of animals. Lamarck’s doctrine of appetency was carried too far, and exposed his views in general to ridicule; he maintained that spontaneous generation takes place at the present time; others have advocated this doctrine since Lamarck, and only within a few years have the researches of Tyndall led him and Huxley, as well as others, to affirm that there is no evidence that the process is now going on. In his famous controversies with Cuvier, Geoffrey St. Hilaire stated his belief in the modification of species by changes in the conditions of life. As successors in Europe may be mentioned the following writers: Wagner, Martins, and Plateau, as well as those given below. . In Germany, the distinguished anatomist, histologist and embryologist, Kdlliker, in his ‘Morphology and developmental History of Pennatulids,’ published in 1872, con- cludes as follows: “Such external forces have operated so as to modify, in many ways, developmental processes, and no theory of descent is complete which does not take these relations into account. Manifold external conditions, when they operate on eggs undergoing their normal development, on larve and other early stages of animals, and on the adult forms, have produced in them partly progressive, partly regressive, transformations. . . . Of such external forces the most important are the mode of life (parasitic and free-living animals, land and water animals), nutrition, light, and heat.” In his History of Creation (1873), Haeckel gives full credit to Lamarck’s views, say- ing: “Without the doctrine of filiation, the fact of organic development in general cannot be understood. We should, therefore, for this reason alone, be forced to accept Lamarck’s theory of descent, even if we did not possess Darwin’s theory of selection.” Here may also be mentioned the researches of Siebold and of Brauer, on the effects of desiccation on the eggs of phyllopod Crustacea, and of Hogg, Dumeril, Wyman, and others, that the metamorphosis of frogs is hastened or retarded by differ- ences in temperature and light. INTRODUCTION. iii Weismann, in his suggestive work, Studies in the Theory of Descent, (1875-76), concludes from his extended investigations on seasonal dimorphism, “that differences of specific value can originate through the direct action of external conditions of life only. . . . A-species is only caused to change through the influence of changing external conditions of life, this change being in a fixed direction which entirely de- pends on the physical nature of the varying organism, and is different in different species or even in the two sexes of the same species.” Weismann has certainly proved that new species arise by differences in climate, while he also (in a note to the English edition) concedes that sexual selection plays a very important part in the markings and coloring of butterflies, but he significantly adds, “that a change produced directly by climate may be still further increased by sexual selection.” A second point, and one of particular interest, which the author claims to be eluci- dated by seasonal dimorphism, is “the origin of variability.” Having shown that “secondary forms are for the most part considerably more variable than primary forms,” it follows that “similar external influences either induce different changes in the different individuals of a species, or else change all individuals in the same manner, variability arising only from the unequal time in which the individuals are exposed to the external influence. The latter is undoubtedly the case, as appears from the differ- ences which are shown by the various individuals of a secondary form. These are,” he adds, giving his proofs, “always only differences of degree and not of kind.” He shows that allied species and genera, and even entire families (Pieride), “are changed by similar external inducing causes in the same manner, or better, in the same direction.” In his Ursprung und ‘der Princip des Functionswechsel, (1875), Dr. A. Dohrn states his belief that new habits induce the organs to exercise apparently new func- tions, which were latent or only partly developed under the original conditions of the surroundings. Another work, laden with facts, with not much space wasted on theories, is Semper’s Animal Life as affected by the Natural Conditions of Existence (1877-81). This is the first general work especially devoted to an attempt to discover the causes of variation in animals. As the author says in his preface, “It appears to me that of all the properties of the animal organism, variability is that which may first and most easily be traced by exact investigation to its efficient causes; and, as it is beyond a doubt the subject around which at the present moment the strife of opinions is most violent, it is that which will repay the trouble of closer research.” An enumeration of the subjects treated in the respective chapters of this work will give one an idea of the way in which this difficult subject should be studied: food and its influence; the influ- ence of light, of temperature, of stagnant water, of a still atmosphere, of water in motion; currents as a means of extending or hindering the distribution of species, and the influence of living organisms on animals. In the United States a number of naturalists have advocated what may be called neo-Lamarckian views of evolution, especially the conception that in some cases rapid evolution may occur. The present writer, contrary to pure Darwinians, believes that many species, but more especially types of genera and families, have been produced by changes in the environment, acting often with more or less rapidity on the organism, resulting at times even in a new genus, or even a family type. Natural selection, act- ing through thousands, and sometimes millions, of generations of animals and plants, liv THE ANIMAL KINGDOM. often operates too slowly; there are gaps which have been, so to speak, intentionally left by Nature. Moreover, natural selection was, as used by some writers, more an idea than a vera causa. Natural selection also begins with the assumption of a ten- dency to variation, and presupposes a world already tenanted by vast numbers of ani- mals, among which a struggle for existence was going on, and the few were victorious over the many. But the entire inadequacy of Darwinism to account for the primitive origin of life-forms, for the original diversity in the different branches of the tree of life-forms, the interdependence of the creation of ancient faunas and floras on geologi- cal revolutions, and consequent sudden changes in the environment of organisms, has convinced us that Darwinism is but one of a number of factors of a true evolution theory ; that it comes in-play only as the last term of a series of evolutionary agencies or causes; and that it rather accounts, as first suggested by the Duke of Argyll, for the preservation of forms than for their origination. We may, in fact, compare Darwinism to the apex of a pyramid, the larger mass of the pyramid representing the true theory, or complex of theories, necessary to account for the world of life as it has been and now is. In other words, we believe in a modified and greatly extended Lamarckian- ism, or what may be called neo-Lamarckianism. It is not the design to present here arguments for this theory of evolution, but to show what American authors have written in favor of the incidental, as well as the periodical, recurrence of sudden or quick evolution, through changes in the environ- ment, as opposed to the supposed continuous action of natural selection. Without doubt, that able and philosophic naturalist, the late S. 5S. Haldeman, was not unfavorable to a modified form of Lamarckian views as to the transformation of species. His Enumeration of the recent fresh-water Mollusca which are common to North America and Europe, with Observations on Species and their Distribution, was published as early as January, 1844. He takes occasion to remark: “I pretend not: to offer an opinion for or against the Lamarckian, being more anxious to show the in- sufficiency of the standing arguments against it, and the necessity of a thorough revision of them, than to take a decided stand (upon a question which I regard as open to farther discussion) before its facts have been carefully observed, or the resulting gen- eralizations properly deduced ; so that, whether it be admitted or not, it is entitled to the benefit of all the discoveries which can be brought to bear upon it; and, on this account, I have not hesitated to give a slight sketch of the theory of transmutation, as I conceive it to be modified by some of the results of modern science.” In the course of his essay he remarks: “The reason why the lower orders still exist is to be looked for in the fact that they are fitted for the circumstances under which we find them.” Again he says: “ Although we may not be able, artificially, to produce a change beyond a definite point, it would be a hasty inference to suppose that a physical agent, acting gradually for ages, could not carry the variation a step or two farther; so that, instead of the original, we will say four varieties, they might amount to six, the sixth being sufficiently unlike the earlier ones to induce a naturalist to con- sider it distinct. It will now have reached the limit of its ability to exist as the former species, and must be ready either to develop a dormant organic element, or die; if the former is effected, the oscillating point is passed, and the species established upon the few individuals that were able to survive the shock. If the physical revolution sup- posed to be going forward is arrested, or recedes, the individuals which had not passed the culminating point remain as a fifth variety, or relapse towards their former station ; whilst the few which have crossed the barrier remain permanently beyond it, even INTRODUCTION. di under a partial retrogression of the causes to which they owed their newly developed organization.” Very significant is the suggestion which follows, as to the cause of comparatively sudden leaps in the process of evolution: We may suppose some species and indi- viduals to be more able to pass than others, and that many become extinct from ina- bility to accomplish it. Under this point of view, a hiatus, rather than a regular passage, is required between a species and that whence it is supposed to be derived, just as two crystals may occur, nearly identical in composition, but without an insensi- ble gradation of intermediate forms; the laws, both of organic and inorganic matter, requiring something definite, whence the rarity of hybrids and monsters, themselves subject to established laws.” He adds, in a foot-note: “The same mineral may crys- talize with three, six, or twelve angles, but not with five or seven. Are the phases of organic morphism subject to less definite laws?” In the year 1850, Professor Joseph Leidy wrote that a slight modification of the essential conditions of life were sufficient to produce the vast variety of living beings upon the globe. In 1853 Dr. Jeffries Wyman published a paper on the effect of the absence of light on the development of tadpoles, and in 1867 appeared his Observations and Experi- ments on Living Organisms in Heated Water. Professor Wyman taught the doctrine of evolution as early as 1861, and probably earlier. In 1864 B. D. Walsh endeavored to establish the fact that, while the great majority of species may have been formed by natural selection, some originated “by changes in the conditions of life, and especially by change of food.” H. J. Clark, in his Mind and Nature (1865), advocated evolution, and even spontaneous generation through physical processes. Professor Alpheus Hyatt (in 1866) showed that the development of the individual in the Ammonites agrees with the development of the order to which it belongs, and he afterward showed, by a study of Ammonites of different geological formations, that just as there are sudden changes of form in the growth of the individual, so species and genera of one formation replace those of another, in such a manner that one form must have descended from the other, although the differences between the forms are very marked. In 1869 Professor E. D. Cope, in his essay on the Origin of Genera, suggested that, by an acceleration or retardation in the development of the animal, generic forms had been produced. He claimed that, “ while natural selection operates by the ‘ preser- vation of the fittest,’ retardation and acceleration act without any reference to ‘fitness’ at all; that, instead of being controlled by fitness, it is the controller of fitness.” He also remarks that the “transformations of genera may have been rapid and abrupt, and the intervening periods of persistency very long;” in other words (p. 80), genera and higher categories have appeared “in geological history by more or ee panray transitions, or expression points, rather than by uniformly gradual successions.” It should be observed, however, that Cope did not enter into the causes which produce acceleration and retardation, but in later papers he has extended and more fully stated his views. Marsh’s observations, published in 1868, on the transformtion of Stredon into the ordinary gill-less salamander (Amblystoma), was astep in the same direction, ¢. e. giving proofs of rapid change in the acquisition of new organs, and modifications of existing ones. lvi THE ANIMAL KINGDOM. In The American Naturalist, for December, 1871, the writer assumed, from a study of cave animals, that these forms were suddenly produced, though the changes may not have been wrought until, say, after several thousand generations; and the theory of Cope and of Hyatt, of creation by a process involving the idea of accelerated de- -velopment in some species, and retarded development in certain organs of other species, was adopted. These views were again enforced in Hayden’s Bulletin of the United States Geological Survey (April, 1877), in an article on the Cave Fauna of Utah. In 1872 the writer (Development of Zimulus), from a study of the paleozoic Crustacea and of the development of Zimulus, claimed that it was impossible “that at the dawn of silurian life these well-marked groups were due entirely to the extinc- tion of multitudes of connecting links, such as Mr. Darwin assumes to have been evolved on the principle of natural selection, with the subordinate agency of sexual selection and mimicry, etc. The groups are almost as clearly marked as in the present time, and such a theory seems to us inadequate to account for the rise of such distinct forms, apparently simultaneous in their appearance at the beginning of the silurian. The forms are remarkably isolated, and present every appearance of having been in a degree suddenly produced,” i. e., by differences in the temperature and depth of the water, etc., the differences being due to changes in the physical surroundings of the organisms. Farther on it is stated: “I conceive these differences to be due, perhaps, to sudden changes of temperature in fresh-water pools, to the difference in the density of fresh and salt water, and the liability of fresh-water pools to dry up, combined with less apparent causes.” It will be seen that these views essentially agree with what is known as Lamarckianism. In his Monograph of the Geometrid Moths, the writer attempted to show that climatic and geological causes were important factors in the production of the genera and species constituting the different faunas. That changes in the physical surroundings of the organism, rather than the strug- gle for existence among the animals themselves, produce new forms of animal life, was also insisted upon by the writer (Half Hours with Insects, 1876), in the follow- ing words : — “When one looks at the beds of fossil beings of the earlier geologic periods, he peers into the tombs of millions which could not adapt themselves to their constantly changing surroundings. No fossil being is known to us which could not have been as well adapted to its mode of life as the animals now living; but the conditions of life changed, and the species, as such, could not withstand the possible influx of new forms, due to some geological change which induced emigration from adjoining territories, or to changes of the contour of the surface, with corresponding climatic alterations. Let one look at the geological map of North America before the cretaceous period, ere the Rocky Mountains appeared above the sea, and reflect on the remarkable changes that took place to the northward, — the disappearance of an Arctic continent, the re- placement of a tropical climate in Greenland and Spitzbergen by Arctic cold. Are there not here changes enough in the physical aspects of our country to warrant such hypotheses of migrations, with corresponding extinctions and creations of new faunas out of preceding ones, as are indulged in by naturalists of the present day, in the light of the knowledge pouring in upon them from Arctic explorers and western geologists? Granted these extraordinary changes in the physical surroundings of the animals whose descendants people our land, do not a host of questions arise as to the result, in the beings of our day, of these changes in the modes of life, the modes of thought, so to speak, the formation of peculiar instincts arising from new exigencies of life, which INTRODUCTION. lvii have remodelled the whole psychology, as it were, of the animals of our country? Instincts vary with the varying structure and form of the animals. Change the sur- roundings, and at once the mode of life and psychology of the organism begin to undergo arevolution. These changes may result in the gradual extinction of whole assemblages of animals, which are as gradually replaced by new faunas.” Mr. J. A. Allen has (in his works on the variation of birds, published in 1871, and especially in subsequent papers) shown the influence of climate and temperature in directly inducing specific changes, without the agency of natural selection. In the American Naturalist for March, 1877, Mr. W. H. Dall published a thought- ful article On a Provisional Hypothesis of Saltatory Evolution. He realizes that “leaps, gaps, saltations, or whatever they may be called, do occur” in the evolution of forms. Mr. Dall remarks that “the apparent leaps which Nature occasionally exhibits may still be perfectly in accordance with the view that all change is by minute differ- ences, gradually accumulated, in response to the environment.” The articles of Mr. W. H. Edwards on dimorphism and seasonal variation in our buttertlies (Canadian Entomologist, 1877) throw light on the production of species by climatic changes, and, with Weismann’s work on this subject, published in Germany, clearly show how many species were called into being by-the geological and especially climatic changes wrought by the advent and departure of the glacial period. All these works show how many are the causes, much more fundamental than natural selection, which have played their part in the origin of the varieties, which have been, however, preserved by natural selection. In his work on sponges (published May, 1877) Professor Hyatt gives a large number of novel facts, showing how greatly sponges are modified in form by the nature of the sea-bottom and the temperature of the water. The same line of thought is extended in his elaborate treatise on the Steinheim shells, published in 1882. It should also be said that Huxley has incidentally observed: “We greatly suspect that Nature does make considerable jumps in the way of variation now and then, and that these saltations give rise to some of the gaps which appear to exist in the series of known forms.” Galton, Mivart, and W. K. Brooks have also favored the view that saltations may occur. Two recent addresses, one by Professor Le Conte of California, and the other by Mr. Clarence King (1877), have forcibly set forth the results upon organic life of the revolutions in the history of the earth. Professor Le Conte, speaking as a geologist, . represents “the organic kingdom as lying, as it were, passive and plastic under the moulding hands of the environment.” He speaks of “general evolution, changes of organisms, whether slow or rapid, as produced by varying pressure of external conditions.” Again, he ably remarks: “There seems good reason to believe that the evolution of the organic kingdom, like the evolution of society, and even of the individual, has its periods of rapid movement and its periods of comparative repose and readjustment of equilibrium.” He illustrates this by referring to the change from the cretaceous to the tertiary period, involving not only a change in climate, but of salt water to fresh, and the extinction of some marine animals, as well as the transmu- tation of others into fresh-water species. Le Conte gives the first place to pressure on the organism resulting from changed physical conditions, and the second place to natural selection. Mr. Clarence King, with his experience as a geologist in the west, has advocated catastrophism in geology, and shows the inadequacy of uniformitarianism in entirely lviii THE ANIMAL KINGDOM. accounting for the epochs of the earth’s history, and he discusses the results of such catastrophic views on evolution. Returning to the consideration of the three factors or fundamental causes bringing about a tendency to variation, we may first consider the changes in the relative distri- bution of land and sea. Geological history is an epitome of the wide-spread and long- continued changes in the shape of the continents, from the time when, as Laurentian land-masses, there appeared but isolated nuclei of what are now the continents. Geol- ogy shows that these primeval incipient continents were original centres of creation, and that however contiguous continents may have borrowed one another’s features, whether to a limited or wide extent, yet, notwithstanding a nearly uniform tempera- ture and climate, the evolution and specialization of life-forms went on throughout the different growing continents, resulting in the zoo-geographical realms of the present day. Here also should be taken into account the elevation of the Hima- layas, the Cordilleras of America, and the Alps and other high mountain chains, producing circumscribed areas, with different climates and other geographical fea- tures. Finally came the Ice period, with the division of the earth’s temperature into tor- rid, temperate, and frigid zones. The changes in the animals and plants resulting from these events must evidently have brought about (1) the extinction of many older types, those unfitted for the new conditions of life; (2) the modification of others more plastic and endowed with greater vitality, while (3) a few forms, such as Linguwla, Ceratodus, etc., endowed with still greater vitality, persisted from early times till now. They were the sole survivors of changes in physical conditions and of a wreckage of life-forms, whose remains fill the cemeteries of paleozoic, mesozoic, and tertiary times. Geological history also shows that there have been periods of long preparation, marked by oscillations of continents, finally terminating in crises. Examples are the accumulations of sediments, their upheaval, metamorphism, and conversion into the Alleghanies, which marked the end of the paleozoic era in eastern North America, The processes of continent-making went on in the eastern hemisphere, beginning at the time when Europe was an archipelago and ending with the period when these islands became united, and Europe and Asia were consolidated into a single continent. The crises in organic life, the origin, rise, culmination, and final extinction of types of organic life, went hand in hand with these great changes in the physical geography of our earth, as seen in the history of the trilobites, of the brachiopods, of the Neba- lids, the Eurypterids, the Dipnoans, and the Labyrinthodonts, ete.; and among plants, the Lepidodendrons, Calamites, Sigillarias, and other extinct forms. Finally, the embryological development and metamorphosis of animals often have a most significant meaning, being condensed histories of changes which must have occurred in the history of their type in past ages. The generalized appearance of the embryo is paralleled by the generalized condition of paleozoic types and their present survivors; the sudden assumption of special characters at or just before the time of birth, is paralleled by the great specialization in form and structure which went on throughout the world in the mesozoic and tertiary times, when forests of club mosses, giant Equiseta, and synthetic, broad-leaved conifers, gave way to growths of modern pines and oaks, beeches, willows, poplars, maples, and other hard-wood trees; while among animals thousands of species of bony fishes, and the whole class of mammals, re- placed the generalized quadrupedal back-boned creatures which haunted the carbon- iferous forests — growths of old-fashioned tree-ferns and club-mosses, with not a flower- INTRODUCTION. lix ing herb or tree to relieve the monotony of the rank, weedy, colossal, but unfinished plants clothing the hills and plains of those days. Thus the whole course of development was from crude, chaotic, generalized forms, both animal and plant, to more elaborate, highly-finished, or specialized forms; this progress towards higher and better things biological going on hand in hand with progress in continent-building, the elaboration of lowlands, plateaus, and mountain chains, until, in the fulness of time, the whole creation revels in marvels of beauty, in a variety so beautiful and delicate as to appeal to the esthetic tastes and to form a training-school in the good, the beautiful, and true for the last product of evolution, that being who has been endowed with sufficient intelligence to read the history of creation, and to look up beyond and above the material world to the Infinite Source of all the physical and evolutional forces which have made the universe. The facts and inductions we have hastily glanced at were established before Dar- win published his Origin of Species. The interpretation now given to them is mainly due to him, who has shown their full significance. As full proofs, however, are the facts regarding the conditions of existence which have been mostly collected by those to whose works we have already referred. These, in the main, are the influence of light or its absence, temperature, parasitism, etc. The study of the effect of these physical agents on organisms is still in its infancy ; the facts can best be observed in external nature, and experimentally in the laboratory. As the result, however, of known facts, it seems evident that the causes of variation, manifold as they seem to be, are such as to be appreciated by the patient and careful observer, and this is the direction which biological research is now taking. Changes in the environment and adaptation to such changes as these, then, are the fundamental causes of the origin of new forms of life. The next factor is the transmission to the offspring of changes thus induced, and to which the organism has become in a slight degree adapted. This is heredity. Of the causes of heredity we know almost nothing. The solution of the problem belongs to the future. The facts are witnessed by every human being. All organisms transmit their own peculiarities as well as those of their race, variety, species, genus, or class to their offspring. Heredity is seen externally in the general shape of the body or trunk, whether stout or slender; in the head and in the limbs, even in the nails and hair, also in the human countenance, in the expression or characteristic fea- tures, as well as in the skin. The Romans, says Ribot, had their Nasones, Labeones, Buccones, Capitones, and other names derived from hereditary peculiarities. Internal peculiarities, such as the shape and size of the bones of the skeleton, and especially the skull and teeth, are hereditary, and even, says Lucas, the heredity of excess or de- fect in the number of the vertebrx and the teeth has been observed. The circulatory, digestive, muscular, and nervous systems obey the same laws, which also govern the transmission of the other internal systems of the organism. There are some families, says Ribot, in which the heart and the size of the principal blood-vessels are naturally very large; others in which they are comparatively small; and others, again, which present identical faults of conformation. The general dimensions of the brain, and even the size and form of the cerebral convolutions, as observed by Gall, are hereditary, and this author in this way accounted for the transmission of mental faculties. Pecu- liarities in the blood-vessels and the blood itself may be transmitted, as seen in the ten- dency in certain families to apoplexy, hemorrhages, and inflammatory diseases: Length of life, fecundity or the opposite trait, is hereditary. In some families the hair \ lx THE ANIMAL KINGDOM. turns gray in early life; immunity from small-pox in some families is said to be a well- established fact; muscular strength, as seen in running, wrestling, and boating, as well as dancing, singing, lisping, loquacity and its opposite, and peculiarities in penmanship and even certain habits besides various physical defects are more or less hereditary ; and artificial deformities, such as flat heads in the North American Indians, while the peculiar methods practised by certain Peruvian tribes, the Aymaras, the Huancas, and the Chinchas, respectively, are known to have been transmitted. Yet there are many exceptions to the law of heredity, especially as regards temporary and accidental modifi- cations, such as circumcision, etc. As a rule, however, not only physical but mental characteristics may be hereditary ; of the latter class are instincts and the senses of color, touch, light, hearing, smell, taste. A strong or weak memory is hereditary ; so also a weak or powerful imagination, peculiarities of intellect, a violent temper or mild dis- position, a strong or weak will, and finally idiocy or genius may run in families. In short, no vital phenomenon, physical or mental, is exempt from the law of hered- ity, yet there are known exceptions, and by care in breeding the domestic animals, as is well known, physical and moral defects can be eliminated, and in mankind good judgment in marriage may result in visible improvement in the stock of certain families. While the causes of heredity are unknown, attempts to account for them have been made by various writers. Says Haeckel: “The cause of heredity is the partial iden- tity of the materials which constitute the organism of the parent and child, and the division of this substance at the time of reproduction.” “ Heredity,” adds Ribot, “in fact, is to be considered only as a kind of growth, like the spontaneous division of a unicellular plant of the simplest organization.” It is evident that in some of the con- ditions of growth we may find an explanation of the fact of heredity. Another phys- ical theory is that of ‘pangenesis’ as proposed by Darwin, who conceives that cells, before their conversion into ‘form material,’ throw off minute atoms which he calls ‘gemmules,’ and which “ may be transmitted from the parent to the offspring,” and as he claims, “are generally developed in the generation which immediately succeeds, but are often transmitted in a dormant state during many generations and are then de- veloped.” Darwin’s gemmules are entirely hypothetical, and, as Galton has observed, the simple experiment of the transfusion of blood, by which a number of ‘ gemmules’ would be inevitably transmitted from one individual to another without the usual results as regards heredity, would seem to prove that pangenesis is “incorrect.” Prof. W. K. Brooks has, in his work on Heredity, restated the hypothesis, as he claims, “in a form which is so modified as to escape this objection.” Intimately connected with the subject of heredity is the fact of reversion or atavism, where a child or young of any animal presents peculiarities evidently inherited not from its parents, but from its grandparent or a remoter ancestor. Cases in point are the occasional appearance, in horses, of stripes on the body and legs, which are supposed by Darwin to have descended from a striped zebra-like ancestor. Darwin gives other examples, and in human families certain traits are known to have jumped over one gen- eration and to descend to the next. It is also a matter of observation that domestic animals allowed to run wild tend to revert to their former feral condition. The third factor in evolution is ‘natural selection.” Since the time of Laban, herdsmen and stock-raisers have been able, by careful selection, matching those cattle, horses, sheep, dogs, etc., which are pre-eminent in desirable qualities, such as speed, size, draft, or, in the case of cows, good milking, either in quality or quantity, INTRODUCTION. lxi to produce strains noticeable for this or that peculiarity useful to their owners. Dar- win applied this law to animals and plants existing in a state of nature, ¢.¢., wild or uncultivated ; and claimed that a process of natural selection is going on bincoughond the world. This phase of evolution is called ‘Darwinism.’ The work entitled The Origin of Species, comprising the results of thirty years of observation and reflec- tion, was published to support and confirm this special theory. We will give a condensed statement of the theory of natural selection, from the author’s own recapitulation of his views, presented at the end of his work (fifth edition, 1871), often using his own words. Domestic animals vary greatly, as the result of changed conditions of life. “This variability is governed by many complex laws — by correlation, by use and disuse, and by the definite action of the surround- ing conditions.” “Man does not actually produce variability; he only unintentionally exposes organic beings to new conditions of life, and then nature acts on the organi- zation and causes variability.” ‘There is no obvious reason why the principles which have acted so efficiently under domestication should not act under Nature. In the survival of favored individuals and races, during the constantly recurring struggle for existence, we see a powerful and ever-acting form of selection. . . . More individuals are born than can possibly survive. . . . As the individuals of the same species come in all respects into the closest competition with each other, the struggle will generally be most severe between them ; it will be almost equally severe between the varieties of the same species, and next in severity between the species of the same genus. On the other hand, the struggle will often be very severe between beings remote in the scale of nature.” “ With animals having separated sexes, there will be in most cases a struggle between the males for the possession of the females. The most vigorous males, or those which have most successfully struggled with their conditions of life, will gener- ally leave most progeny. But success will often depend on the males having special weapons or means of defence, or charms; and a slight advantage will lead to victory.” He then claims that, as geology shows that each land has undergone great physical changes, we might have expected to find that organic beings have varied under Nature in the same way as they have varied under domestication. “If, then,” he says, “ani- mals and plants do vary, let it be ever so little or so slowly, why should we doubt that the variations or individual differences, which are in any way beneficial, would be preserved and accumulated through natural selection, or the survival of the fittest? IE man can by patience select variations useful to him, why, under changing and complex conditions of life, should not variations useful to Nature’s living products often arise, and be preserved or selected.” It is impossible, without the evolution theory, to explain the meaning of rudimen- .tary organs. “ Disuse, aided sometimes by natural selection, has often reduced organs, when they have become useless under changed habits or conditions of life; and we can clearly understand on this view the meaning of rudimentary organs. But disuse and selection will generally act on each creature when it has come to maturity, and has to play its full part in the struggle for existence, and will thus have little power on an organ during early life: hence the organ will not be reduced or rendered rudi- mentary at this early age. The calf, for instance, has inherited teeth which never cut through the gums of the upper jaw from an early progenitor having well-developed teeth; and we may believe that the teeth in the mature animal were reduced, during successive generations, by disuse, or by the tongue and palate or lips having become lxii THE ANIMAL KINGDOM. better fitted by natural selection to browse without their aid; whereas, in the calf, the teeth have been left untouched by selection or disuse, and, on the principle of inheri- tance at corresponding ages, have been inherited from a remote period to the present day. On the view of each organic being, with all its separate parts, having been specially created, how utterly inexplicable it is that organs bearing the plain stamp of inutility, such as the teeth in the embryonic calf, or the shrivelled wings under the soldered wing-covers of many beetles, should so frequently occur! Nature may be said to have taken pains to reveal her scheme of modification by means of rudimen- tary organs, embryological, and homological structures, but we wilfully will not understand the scheme.” We will finally quote the very noble words with which Darwin concludes this volume: “There is grandeur in this view of life, with its several powers, having been originally breathed by the Creator into a few forms, or into one; and that, while this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning, endless forms most beautiful and most wonderful have been and are being evolved.” HISTORY OF ZOOLOGY. Zoology as a descriptive science dates from the time of Linneus, the father of natural history, but as a well-grounded science it is scarcely older than 1839, the date of Schwann’s work on the cell, and the period of the manufacture and wide- spread use of good compound microscopes. After the descriptive era of Linnwus and his successors, arose the era of comparative anatomy and paleontology, twin branches of biology, engrafted by Cuvier on the tree of zoological knowledge, which was planted, so to speak, by Linnzeus. Then arose the branches of histology, embryology, and gen- eral morphology. The predecessors of Linnzus, or Carl von Linné, were Malphigi, Leeuwenhoek, Swammerdam, and Redi, who flourished before Linnzeus was born (1707). Before the birth of Linnzus, also, there was a general scientific renaissance, which resulted in the foundation of academies of science; the oldest German scientific society being the Academia Nature Curiosorum, founded at Halle in 1652. ‘Ten years later (1662), the Royal Society of London was founded. In France, Richelieu founded, as early as 1633, the Académie Frangaise for the promotion of the French language and litera- ture; in the reign of Louis XIV. the Académie des Sciences was founded; its first volume of works bears the imprint Paris, 1671. Three other academies were estab- lished in Paris, and the five were united under the name of the Institute Frangais. Then followed the founding of the scientific societies and academies of Berlin (1700), Upsala (1720), St. Petersburg (1725), Stockholm (1789), Copenhagen (1743), and Bologna, whose Commentaries first appeared in 1731. The history of zoology may be roughly divided into several periods : — 1. Period of systematic zoology.— While it should not be forgotten that Aristotle gave the name Mollusca to the group still bearing that name, no naturalist of mark arose until Linnzus was born. In England, Linnus was preceded by Ray, but bi- nomial nomenclature and the first genuine classification of animals dates back to the Systema Nature, the tenth edition of which appeared in 1758. As the result of his influence, his own pupils, and also the German traveller and naturalist Pallas, did much to advance zoo-geography ; while the anatomists and physiologists of this period were Camper, Spallanzani, Wolff, Hunter, and Vicq d’Azyr, the last-mentioned author being the first to propose the term ‘ comparative anatomy.’ INTRODUCTION. lxiii 2. Period of comparative anatomy and paleontology. — Cuvier, born in 1769, was the founder of the twin sciences of comparative anatomy and paleontology, and at Paris centred the great lights of comparative anatomy, Geoffrey Saint-Hilaire, La- marck, Bichat, Vicq d’Azyr, Blainville; France then leading the scientific world, though Germany had her Blumenbach, Déllinger, Tiedemann, Bojanus, and Carus. Meckel, at his time the leading German anatomist and compiler, studied at Paris with Cuvier, and so did Richard Owen of England, and Milne-Edwards of France. Both the latter are still living, Sir Richard Owen, in his eightieth year, being still prolific in monographic memoirs, both morphological and paleontological. Among writers on the doctrine of animal types, who flourished in the first third of the present century, were Lamarck, Cuvier, Blainville, and Von Baer. During this period the science of embryology began to take form under the inspiration of Oken, Pander, Dillinger, Von Baer, Rathke, and Wolff; this work was carried on in later years by Coste, Bischoff, Reichert, Kélliker, Vogt, and Agassiz. The great activity shown at Paris by Cuvier in the building up of the Jardin des Plantes, led to the French exploring expeditions sent out from 1800-1832 to all parts of the world, resulting in enlarged views regarding the number and distribution of species, and their relations to their environment. The zoologists who went on these expeditions were Bory de St. Vincent, Savigny, Péron, Lesueur, Quoy, Gaimard, Vail- lant, Eydoux, and Souleyet. From 1823-1850 England fitted out exploring expedi- tions under Beechey, Fitzroy, Belcher, Ross, Franklin, and Stanley, the naturalists of which were Bennett, Owen, Darwin, Adams, and Huxley. Russia (1803-1829) sent out expeditions to the north and northeast, accompanied by the naturalists Tilesius, Langsdorff, Chamisso, Eschscholtz, and Brandt, all of them of German birth and education. The United States exploring expedition under Wilkes (1838-1842) was, in scientific results, not inferior to any previous ones, the zoolo- gists being Dana, Couthuoy, and Peale. Of a later voyage under Ringgold, Stimpson was the naturalist, but the rich final results were lost by fire. At or near the close of this period, from Germany, Humboldt, Spix, Prince Wied-Neeuwied, Natterer, Perty, Reugger, Tschudi, Schomburgk, Burmeister; from France, de Azara, d’Orbigny, Gay, Castlenau; and from Denmark, Lund, — travelled at their private expense, an evidence of the spirit of scientific research then dominating the centres of civilization. Their followers in the present time have been Wallace, Semper, Bates, Michlucho-Maclay, Prezvalsky, and many others. Towards the middle of the century, the leading comparative anatomist and physi- ologist was Miller of Berlin. Now began to dawn the modern period of morphology and embryology, under his inspiration, and that of Savigny, Sars, Rathke, Agassiz. General text-books on comparative anatomy, compiled by leading authorities, are R. E. Grant’s Lectures on Comparative Anatomy (1833-4), Wagner’s (1834-5), Owen’s Lectures on the Comparative Anatomy of the Invertebrates (1843 and 1855), and Anatomy of Vertebrates (1866-68); Siebold (invertebrates) and Stannius (verte- brates) (1845-46); Rolleston’s Forms of Animal Life (1870); Huxley’s Anatomy of the Vertebrates (1871), and Invertebrates (1877); finally the list culminates in the suggestive work of Gegenbaar (1874), entitled Elements of Comparative Anatomy, and written from the modern morphological and evolutional standpoint. The lead- ing text-books of systematic zoology are those of Van der Hoeven (1850), Carus, and Gerstaecker (1863-75), and lastly that of Claus (1868-84). The great encyclo- pedic work, Classen und Ordnungen der Thierreichs, planned and begun by Bronn, lxiv THE ANIMAL KINGDOM. and continued by Gerstaecker, Hoffmann, Giebel, Hubrecht, Vosmaer, Biitschli, and others, is a fitting embodiment of the results of higher zoological studies from Lin- neeus to the present time. 8. Period of Morphology and Embryology. — This period has been distinguished (1) by the application of the discovery by Schwann of the cellular theory of organized beings, especially to animals, and the studies of Dujardin and W. Schultze on the nature of protoplasm, proving that the cell is the unit of organization, and that protoplasm is the basis of life; (2) by the application of histological discoveries and methods to embryological research, and (8) by the application of the doctrine of evolution as a working theory to account for the common origin of animals from a single simple organism. If single names are to be mentioned where in fact many have worked together to accomplish these results, the names of Schwann, of Dujardin and Schultze, and that of Darwin come first to mind. In 1665 Robert Hooke distinguished the cells of plants, calling them “cells and pores,” and comparing them to honey-comb. Schwann was the first to discover animal cells. Schwann first (1839) called the nucleus ‘kérperchen,’ but Valentine in the same year (1839) invented the terms nucleus and nucleolus, since then in uni- versal use, and Valentine was the first, in his review of Schwann’s work in the Repertorium for 1839, to speak of ‘the cellular theory.’ In Carnoy’s La Biologie Cellulaire (1884) we find a convenient summary of the history of the discovery of protoplasm and the doctrine that it forms the living matter common to vegetable and animal cells. In 1835 Dujardin thus characterized this substance: “I propose to name sarcode that which other observers have called a living jelly, this glutinous, transparent, homogeneous substance, which refracts light a little more readily than water, but much less than oil; which is extensible and can stretch itself like mucus, is elastic and contractile, is susceptible of spontaneously forming spherical cavities or vacuoles, filled with the surrounding liquid, which some- times forms of it an open network. . . . Sarcode is insoluble in water; at length, however, it ends by decomposing and leaving behind a granulous residue. Potassium does not suddenly dissolve it, as it does mucus or albumen, and appears only to hasten its decomposition by water; nitric acid and alcohol suddenly coagulate it and render it white and opaque. Its properties are then very distinct from those of substances with which some authors have confounded it, for its insolubility in water distinguishes it from albumen, and its insolubility in potash likewise distinguishes it from mucus, gelatine, etc. . . . The most simple animals, amebas, monads, etc., are wholly com- posed, at least in appearance, of this living jelly. In the higher Infusoria it is con- tained in a loose tegument which opens on its surface like a network, and through which it can pass out in a state of almost perfect isolation. . .. We find sarcode in eggs, zoophytes, worms and other animals; but in these it is susceptible of receiving with age a degree of organization more complex than in animals lower in the scale. . . . Sarcode is without visible organs, and without appearance of cellulosity; but, however, it is organized, because it throws out divers prolongations, drawing along in them granules, alternately extending and retracting them, and, in a word, it has life.” The observations of the past fifty years have made little change in Dujardin’s characterization of this substance, but his name has become well nigh forgotten, and for it has been substituted the word protoplasm. This new word was first bestowed upon it by Purkinje in 1839-40. Afterwards the celebrated botanist Hugo von Mohl, ignorant of the existence of the word, said in 1846 (Bot. Zeitung), “I believe myself INTRODUCTION. lxv authorized to give the name of protoplasm to the semi-fiuid substance, azotic, made yellow by iodine, which is spread throughout the cellular cavity, and which furnishes the material for the primordial utricle and nucleus.” Thus a comparative anatomist and a botanist each independently applied the same name to the living substance com- mon to both animals and plants. Dujardin’s researches attracted great attention, and in 1861 Max Schultze did not hesitate to affirm the identity of animal cells in general with sarcode. Brticke (1861), Schultze (1863), and Kihne (1864), finally demonstrated the identity of living mat- ter in the two kingdoms, as to its fundamental physical properties: irritability and contractility. Since the beginning of the second half of this century (1850-1884), zoological science has been developed with great rapidity in all directions, but in none more than in embryology and morphology, while the number of workers has vastly increased. Moreover, the general respect and sympathy for biological research, felt by all edu- cated minds, has encouraged the active workers; hence the formation and endowment of new academies and societies, the establishment and support of journals of advanced m>rphology ; the building and rearrangement of museums, and the installation of labor- atories for original research. Private explorations in all parts of the earth, and the numerous surveys, especially those of the United States, both state and national, have fostered and extended zoological knowledge. Several general treatises on embryology have been published, by Wolff (1759), Von Baer, Agassiz, Haeckel and Packard, but the last of these treatises, Balfour’s Compar- ative Embryology, is an epoch-making work on development, indicating the third stage in the history of biological science; Wolff’s marking the first, and Von Baer’s the second. The great steps in the discovery of the way animals reproduce and develop were the discovery of spermatozoa by Leeuwenhoeck in 1677, and that of the mammalian egg by Degraaf in 1673. A century and a half later Von Baer confirmed the latter, and showed that all mammals develop from eggs, and then Coste, Valentin, and Jones showed that these eggs were homologous with those of the lower vertebrates. The next step was the discovery by Remak, in 1850, of the three germinal layers; then Huxley, in 1859, homologized these with the tissues of the celenterates. The last steps to be mentioned are investigations of the brothers Hertwig on the meso- blast and the celom, and those of Lang and of Sedgwick on metameric segmentation and the homology of the blastopore throughout the animal kingdom. While the future will doubtless produce many important discoveries, and corrections of existing errors, it would seem that the leading features of embryology are already established. The earlier writers on evolution were Lamarck, Geoffrey St. Hilaire, and Goethe. The literature of evolution, which has characterized the second half of this century, is the scientific offspring of Darwin’s Origin of Species, which appeared in 1859, a pre- liminary essay by Darwin and by Wallace being offered the previous year. It is the leaven which has leavened the whole lump of modern scientific and philosophical thought. It was the work of a zoologist; whose studies of systematic and anatomical zoology as well as geographical distribution converged toward the conception that species had originated from natural causes. Alfred R. Wallace, also, as the result of his travels and researches on the Amazon River, and especially in the Malay archipel- ago, arrived nearly simultaneously at the same conclusion; his original essay written at Sarawak in 1855, with others, collected in 1870, are entitled Contributions to the xvi THE ANIMAL KINGDOM. Theory of Natural Selection, while H. W. Bates, after spending eight years of re- search and travel in Brazil, was also led to adopt the theory of natural selection. Fritz Miller (ftir Darwin, dated Desterro, Brazil, 1863) and his brother, the late Her- mann Miller, in numerous botanico-entomological tracts and works, as well as Haeckel in his History of Creation, his Anthropogeny, and other works, and Weissmann’s Studies in the Theory of Descent (1875) are the. epoch-making works of this period, based, as they are, on special studies. Expounders of the doctrines were Huxley (1859), Herbert Spencer, Haeckel, Asa Gray, and many others. Of the rise of a modernized Lamarckian school in the United States, of which Hyatt, Cope, Dall, Ryder, and Packard are the supporters, mention has already been made. In Germany this school is represented especially by Semper. . With a knowledge of zoological classification and embryology, naturalists have, since the publication of Darwin’s epoch-making work on the origin of species, published theories as to the probable ancestry and succession of forms, and entered into the con- struction of genealogical trees, or, in a word, of phylogenies. Haeckelin 1870 first dared to express diagrammatically his views as to the phylogeny of animals in general, his most authoritative work relating to the celenterates, especially the meduse. Attempts to trace the genealogy of the insects have been made by Brauer, Packard, Lubbock, and Mayer; Hyatt has elaborated the phylogeny of the Ammonites, and Owen, Hux- ley, Kowalevsky, and Marsh the ancestry of certain ungulates, especially of the horse family, while the phylogenies of the Camelidx, the Carnivora, the Ungulata in general, and other orders, have been worked out by Cope. The effect of these studies on paleontology has been marked, and have given a new direction to the study of the geological succession of animals. The great works of James Hall, of Barrande, of the Surveys of India, and the explorations in the western tertiaries by Hayden, which were published by Meek, Leidy, and others, and the per- sonal explorations of Marsh and of Cope, as well as those of Gaudry in Europe, have re- vealed numbers of forms connecting the orders of living reptiles, birds, and mammals, while the researches on the succession and ancestry of the Ammonites by Hyatt have opened new fields of research. In 1864 the Norwegian naturalist, M. Sars, and his son, G. O. Sars, carried on dredging to the depth of over 300 fathoms, showing that Forbes (before that time the most prominent writer on marine zoology and the laws of bathymetrical distribution), was incorrect in inferring that the sea below the depth mentioned was barren of life. As early as 1850, Michael Sars opposed Forbes’ hypothesis, and in 1864 published a list of 92 different species discovered at 200-300 fathoms on the coast of Norway, and in 1868 he increased the list to 427 species. As the results of his father’s and his own examinations, Prof. G. O. Sars, as early as 1869, said: “ The results of these, my deep- sea researches, was, however, great and interesting quite beyond all anticipation. . . . And so far was I from observing any sign of diminished intensity in this animal life at increased depths, that it seemed, on the contrary, to me as if there was just beginning to appear a rich and in many respects a peculiar deep-sea fauna, of which only a very incomplete notion had previously existed.” The United States Coast Survey, since 1867, under the inspiration and labors of Agassiz and Pourtales, showed that the bottom of the Floridan channel, below 800-500 fathoms, was packed with life- forms; the Swedish Spitzbergen expeditions also brought up deep-sea animals from 2000-8000 fathoms. Meanwhile, the English government sent out the ‘ Porcupine’ and other vessels, the naturalists of which were Carpenter and Jeffreys, who carried on INTRODUCTION. lxvii extensive deep-sea explorations in the North Atlantic, which were so successful and full of interest as to stimulate the British government to equip and send out, under the scientific direction of Wyville Thompson, aided by W. von Suhm, Moseley and others, the ‘ Challenger,’ which made a voyage around the globe in 1872-76. The results were full proof of the existence, in all seas throughout the world, of a fauna unique and extensive, generally known as the abyssal fauna, thus adding a new world of life, with previously unknown orders of animals, involving new problems in » paleontology and biology, and immeasurably extending our conceptions of the world and its inhabitants and their mutual relations. The voluminous results of this most important of all the voyages of scientific discovery, since that of Columbus, are still incomplete. Important additions to the facts gathered by the ‘Challenger’ and pre- vious explorations, have been made by the Swedish expedition of the ‘ Josephine,’ the naturalists of which were Smith and Ljungmann, and by the U. 8. Commission of Fish and Fisheries, 8. F. Baird, Commissioner, of which A. E. Verrill, in charge of the in- vertebrates, has from time to time published important results. The Austrian, Portuguese, and French governments have sent out similar expedi- tions, of which, perhaps, the voyage of the ‘Talisman,’ in 1883, obtained the richest results, A. Milne-Edwards being the naturalist in charge. Extensive researches with the dredge along the coast of the United States were made by Agassiz, Desor, and especially Stimpson, from the Bay of Fundy, to Florida, Cuba, and Yucatan; Packard investigated the shoal-water fauna of Labrador in 1860-64 ; while Verrill, Hyatt, Packard, and others have dredged the coast from the Gulf of St. Lawrence to Cape Hatteras. The economic value attached to the fisheries led to the formation of the Fisheries Commissions of Norway, Germany, and the United States; that of the latter, under Baird, being especially rich in purely scientific results. The ravages of injurious insects, involving economic questions of vast moment, have attracted attention from time immemorial. The destruction of crops and of forests by these pests led Ratzeburg to devote his life to the subject, resulting in the preparation of the monumental tomes, richly illustrated and replete with facts, which have given him an enduring fame. The works of Bouché, Boisduval, and others in Europe, and of Harris in this country, are also classics. In America, ‘the state governments established the office of state entomologists, whose reports, particularly those of Fitch, Walsh, and Riley, are standard works of reference. The invasion of locusts in the western states and territories led the national government to establish the U. 8S. Entomological Commission, consisting of Riley, Packard, and Thomas, which existed for five years (1877-81). In 1873 Agassiz established at Penikese, an island in Buzzard’s Bay, a seaside labor- atory for teachers and for students of marine animals. After two years it ceased to exist. It led to the formation of the Chesapeake Zoological Laboratory of the Johns Hopkins University, under the direction of Prof. W. K. Brooks, while Mr. A. Agassiz built a well-appointed private laboratory at Newport. Led by Agassiz’s example, Anton Dohrn established the costly zoological station at Naples, where gather natural- ists of different countries, whose researches, carried on under such favorable auspices, have had a manifest influence on morphological studies. Smaller laboratories have been established by Lacaze Duthiers at Roscoff, Banyul sur Mer in France, and by Hyatt at Annisquam, in Massachusetts; while during the years 1876-81 a summer school of biology founded by Packard, was carried on by the Peabody Academy of Science at Salem, Massachusetts. lxviii THE ANIMAL KINGDOM. Let us now review in a brief manner the work done by our countrymen. Ameri- can zoological science dates only from 1796, when Barton published his memoir On the Fascination attributed to the Rattlesnake, while his Facts, Observations, and Conjectures on the Generation of the Opossum appeared in 1801. These were simply memoirs, but still talented productions and not unworthy to begin the century. Previous to this, John Bartram published a few zoological tracts in the Philosophical Transactions of the Royal Society of London, the first appearing in 1744. American systematic zoology may be said to date from the years 1808-14, when the successive volumes of Wilson’s Ornithology were published, though it should be remembered that Wilson was born and bred in Scotland. Thus, with the exception of Bartram’s and Barton’s works, what we have to say of American zoology (includ- ing animal physiology, psychology, and embryology) covers only about three quar- ters of a century. The next work was by Prince Bonaparte, on birds, a volume supplementary to Wilson’s great work, and published in this country in 1825-38. The first general work by a native-born American was Dr. Richard Harlan’s Fauna Americana, published in 1825. This was succeeded by Dr. John D. Godman’s work on North American mammals, published in three volumes in 1826-28. Bartram, Barton, and Harlan were born in Philadelphia and taught anatomy there. Godman was born in Annapolis, and lectured on anatomy in three medical colleges, but not in Philadelphia. Thomas Say’s American Entomology (1824-28) was of a more special character. On the whole, American zoology took its rise and was fostered chiefly in Philadelphia by the professors in the medical schools; and zoology the world over may be said to have sprung from the study of human anatomy as taught at the ana- tomical centres of Italy, France, England and Germany. The last half-century of progress in zoology in America may be divided into three epochs comparable to those enumerated on a preceding page :— (1.) The epoch of systematic zoology, during which a few physiological essays ap- peared. To this division of zoology a most decided impulse was given by the Smithsonian Institution, which went into active operation in 1847, while the study of the fossil forms (paleontology) was greatly accelerated by the influence of national and especially state surveys. (2.) The epoch of morphological and embryological zoology. This period is due to the arrival of Louis Agassiz in this country, in 1846, resulting in his lectures on comparative embryology and the foundation of the Museum of Comparative Zoology, where American students, who were attracted by the fame of Agassiz, were instruct- ed in the methods of Cuvier, Von Baer, Déllinger, and Agassiz himself, and zoology was studied from the side of histology and embryology, while paleontology was wedded to the study of living animals. (3.) The epoch of evolution, or the study of the genetic relationship of animals, based on their mutual relations and their physical environment. This period dates from the publication of Darwin’s Origin of Species, in 1859. Turning, now, to the first epoch,— that in which American systematic zoology took its rise, —we find that work was done which must necessarily precede more important studies on the embryology, geographical distribution, mutual relations, and psychology of animals ; thus exerting a marked influence on the classification of animals, which nowadays is equivalent to tracing their genetic relationships; for the time is past when the animal world should be regarded as comprised within separate sub- kingdoms, between which there is no morphological or genetic connection. INTRODUCTION. Isis The systematic works are so well known, and our space so limited, that we shall merely enumerate the names of our chief zoological authors. In the study of mam- mals the works of Audubon and his predecessors, already named, and of Thomas Jef- ferson, T. Say, J. Bachmann, G. Ord, 8. F. Baird, T. Gill, Harrison Allen, J. A. Allen, E. D. Cope, Elliott Coues, J. Y. Scammon, B. G. Wilder, C. H. Merriam, and W. 8. Barnard, should be mentioned, with the paleontological essays of R. Harlan, J. C. Warren, J. Leidy, E. D. Cope, and O. C. Marsh, together with Godman’s Rambles of a Naturalist, L. H. Morgan’s work on the beaver, Merriam’s on the Mammals of the Adirondacks, and physiological essays by J. Wyman, 8S. Weir Mitchell, J. C. Dalton, and others. The ornithological works of Wilson, Bonaparte, Audubon, Nuttall, Baird, Cassin, and Coues, the more recent great work of Baird, Brewer, and Ridgway, Coues’ Key to the North American Birds, Birds of the Northwest, and Birds of the Colorado Valley, and the many descriptive and biological papers of other authors, such as T. M. Brewer, Ord, J. P. Giraud, J. K. Townsend, A. L. Heerman, G. N. Lawrence, D. G. Elliott, H. W. Gambel, J. Xanthus, L. Stejneger, H. W. Henshaw, H. Byrant, S. Cabot, T. M. Trippe, J. A. Allen, C. H. Merriam, W. H. Brewster, and others, with the papers on distribution by Baird, A. E. Verrill, J. A. Allen, and R. Ridgway, together with those on fossil birds by Marsh, are all worthy of comparison with the best European works and papers. The reptiles and amphibians have been described by Harlan, J. E. Holbrook, T. Say, J. Green, Baird, C. Girard, 8. Garman, E. Hallowell, L. R. Gibbes, C. A. Lesueur, J. L. Le Conte, L. Agassiz, and Cope, and an entire assemblage of forms in the west- ern cretaceous and tertiary formations has been discovered by Leidy, Marsh, and Cope. The anatomy of the nervous system of Rana pipiens, by Jeffries Wyman, is a classic, as are the researches of 8. Weir Mitchell upon the venom of the rattlesnake, and the researches on the anatomy and physiology of respiration in the Chelonia, by 8S. Weir Mitchell and G. R. Morehouse. The fishes of North America have been worked up by 8. L. Mitchell, Lesueur, C. S. Rafinesque, D. H. Storer, J. E. Dekay, Holbrook, Agassiz, Girard, J. P. Kirtland, J. C. Brevoort, Wyman, Baird, Gill, Cope, W. O. Ayres, F. W. Putnam, T. G. Tell- kampf, D. 8. Jordan, H. C. Yarrow, C. C. Abbott, G. B. Goode, R. Bliss, 8. W. Gar- man, W. N. Lockington, C. H. Gilbert, J. H. Swaim, and others; while the fossil forms have been described by J. H. and W. C. Redfield, Leidy, R. W. Gibbes, J. 8. Newberry, Cope, O. St. John, E. W. Claypole, and others, and several species of Tunicata have been described by C. A. Lesueur, Tellkampf, Louis and A. Agassiz, Verrill, and Packard. In entomology the writings of Say, the two Le Contes, F. E. Melsheimer, N. Hentz, T. W. Harris, 8. 8S. Haldeman, R. von Osten Sacken, B. Clemens, J. D. Dana, G. H. Horn, 8. H. Scudder, P. R. Uhler, H. Hagen, B. D.{Walsh, A. 8. Packard, A. R. Grote, W. H. Edwards, Henry Edwards, C. H. Fernald, H. C. Wood, A. Fitch, C. V. Riley, E. Norton, J. H. Emerton, C. Thomas, 8. W. Williston, R. H. Stretch, H. Strecker, J. B. Smith, J. H. Comstock, L. O. Howard, E. T. Cresson, and others, are in most cases quite voluminous, though mostly descriptive, while the fossil forms have been described by Scudder, Dana, Meek and Worthen, 8. I. Smith, and O. Harger. Their anatomy and histology has been studied by Leidy, Scudder, Packard, G. Dim- mock, E. Burgess, C. 8. Minot, and G. Macloskie. The great work of Dana on the Crustacea of the United States Exploring Expe- Ixx THE ANIMAL KINGDOM. dition placed him next to Milne-Edwards at the head of living authors in this depart- ment, and his essay on their geographical distribution is the starting-point for all such inquiries. The North American species have been described by Say, W. Stimpson, J. W. Randall, L. R. Gibbes, 8. I. Smith, Hagen, W. N. Lockington, E. A. Birge, C. L. Herrick, W. Faxon, Packard, O. Harger, and J. 8. Kingsley, and the fossil forms by Green, Hall, Billings, Stimpson, Packard, C. E. Beecher, Clarke, C. D. Walcott, and others. The intestinal and higher worms have been worked up by D. Weinland, Girard, Leidy, Wyman, Verrill, Stimpson, Minot, Webster, Benedict, Sager, Whitman, and Wright; and of the aberrant classes some of the Polyzoa have been carefully studied by A. Hyatt, and the Brachiopoda by E. 8. Morse and W. H. Dall. The molluscs of North America have been elaborated by Say, Gould, Lesueur, Rafinesque, Haldeman, I. Lea, T. A. Conrad, Anthony, C. B. Adams, Stimpson, the two Binneys, J. W. Mighels, J. P. Couthouy, Gabb, A. Agassiz, T. Bland, T. Prime, Morse, J. Lewis, Dall, Tryon, Verrill, R. E. C. Stearns, Sanderson Smith, and others. The fossil Mollusca of entire formations have been described by Hall, Billings (of Canada), F. B. Meek, C. A. White, F. 8. Holmes, O. St. John, C. F. Hartt, R. Rath- bun, O. A. Derby, Whitfield, N.S. Shaler, Whiteaves (of Canada), and other palzon- tologists; and the quaternary species studied by Holmes, Dawson, Stimpson, Packard, Verrill, Matthews, and others. Their anatomy has been studied by Leidy, Wyman, Morse, Dall, W. K. Brooks, and H. L. Osborn; while B. Sharp has studied their visual organs. The celenterates and echinoderms have been carefully elaborated by Louis and A. Agassiz, and by Say, Stimpson, E. Desor, Ayres, Macrady, H. J. Clark, T. Lyman, Pourtales, Verrill, W. Ix. Brooks, 8. F. Clarke, E. B. Wilson, J. 8S. Kingsley, J. W. Fewkes, H. W. Conn, and H. G. Beyer; while Dana’s elaborate report on the Zoo- phytes of the United States Exploring Expedition took the highest rank among syste- matic works. Numerous fossil forms have been brought to light by Hall, Billings, Meek, Shumard, Springer, White, Wachsmuth, Whitfield, W. H. Niles, O. A. Derby, and other paleontologists, and the distribution of the recent forms on both sides of the continent has been studied by Verrill and A. Agassiz. The sponges have been chiefly studied by Clark, Hyatt, Potts, and Mills; and the Protozoa by Leidy, J. W. Bailey, H. J. Clark, A. C. Stokes, J. A. Ryder, and D.S. Kellicott. We may congratulate ourselves on the high position of our paleontologists in the scientific world. The labors of James Hall, Mcek, Billings, Dawson (of Montreal; we include Canadian students), and others, have revealed whole platforms of life in the paleozoic rocks; while the researches of Leidy, Cope, Marsh, and W. B. Scott and H. F. Osborne, in the tertiary, cretaceous, and Permian beds of New Jersey and the west, and of Deane, Hitchcock, Leidy, Wyman, Newberry, Emmons, and Cope, in triassic and carboniferous strata, have been productive of valuable results. The discovery of the fossil bird-like reptiles of New Jersey, by Leidy and Cope; of birds with teeth, and pterodactyls without teeth; of lemur-like monkeys, by Marsh; of camels, by Cope; and the discovery by Leidy, Marsh, and Cope, of con- necting links between living ruminants and hog-like forms, and between elephants and tapirs; together with the genealogy of the horse, and the increase in the size of the brain of living forms over their tertiary ancestors, as elaborated by Marsh, all present a mass of new facts bearing on the evolution of life on the American continent, and INTRODUCTION. lxxi the general doctrine of evolution. The labors of W. B. Scott and H. F. Osborne should also be mentioned here. The epoch of embryology, or the developmental study of animals, was inaugurated by Agassiz in 1846. In the publication of his Contributions to the Natural History of the United States, mainly devoted to the developmental history of the celenter- ates and turtles, Agassiz was assisted by H. J. Clark. Macrady, another of Agassiz’s students, published some papers of importance on the Acalephs and their mode of development. Desor and Girard wrote on the embryology of worms. Memoirs of a high order of merit followed from the pen and pencil of Mr. Alexander Agassiz. His embryology of the echinoderms appeared between 1864 and 1874; the memoir on the alternation of generations of the worm, Auéolytus, appeared in 1862; his paper on the early stages of annelids in 1866; his remarkable memoir on the transformation of Tornaria into Balanoglossus was published in 1873; and his elaborate embryology of the Ctenophores in 1874. In 1864, Jeffries Wyman, at the time of his death the leading American comparative anatomist and physiologist, published a memoir on the development of the skate. Studies on the development of worms have been made by J. W. Fewkes and E. B. Wilson, while J. A. Ryder, A. Agassiz, C. O. Whitman, H. J. Rice, J. S. Kingsley, and H. W. Conn, have worked on the embryology of fishes. That of the Amphibia has been elaborated by S. F. Clarke, W. B. Scott, and H. F. Osborn, and their transformations by Mary Hinckley. The beautiful memoir of Hyatt on the embryology of Ammonites was a difficult research, while the papers of Morse on the early stages of the brachiopod, Terebratulina, published in 1869-73, led him, by embryological as well as anatomical evidence, to transfer the brachio- pods from the molluses to the vicinity of the annelidan worms. Morse and W. K. Brooks have also examined the development of Zingula. The studies of Morse on the carpus and tarsus of embryo birds should also be mentioned. In 1870, 1872, and 1880, Packard published memoirs on the development of Zimulus, and was the first to point out the affinities of its young to certain young trilobites; and he has also published papers on the embryology of the hexapodous insects. Of a high order of merit are Howard Ayres’ elaborate memoir on the development of the Gcanthus niveus, or tree cricket, with its egg parasite (1884), and William Patten’s valuable essay on the embryology of the Phryganeide (1884). 8. I. Smith, W. K. Brooks, W. Faxon, E. A. Birge, and E. B. Wilson have traced the metamorphoses of certain Crustacea. Several entomologists, as Harris, L. Agassiz, Fitch, Riley, Scudder, Packard, Le Baron, Hagen, Cabot, Walsh, Saunders, W. H. Edwards, Henry Edwards, 8. A. Forbes, J. A. Lintner, Otto Lugger, and others, have studied the metamorphoses of insects, while the drawings in illustration of Abbot and Smith’s Natural History of the Rarer Insects of Georgia were made by Abbot, who lived several years in Georgia. In 1874 Emerton described the embryology of the spider, Pholcus, and in 1876 an impor- tant memoir by W. K. Brooks, on the anomalous mode of development of Saipa, a tunicate, appeared. J.S. Kingsley has described the metamorphoses of the ascidian, Moigula. The embryology of the molluscs, especially of the oyster, has been worked out by W. K. Brooks and J. A. Ryder, while E. B. Wilson has treated that of Renilla. Mention should also be made of the papers by J. W. Fewkes and 8. F. Clarke on the development of celenterates. In the department of embryology, great activity was shown by American students when scarcely anything was being done in England or France, and the United States were for twenty-five years (1850-1875) only second in embryological studies to Germany, the mother of developmental zoology. More lxxii THE ANIMAL KINGDOM. recently England, through the labors of Balfour and his pupils, has advanced to a posi- tion far ahead of the United States. Of anthropological authors, we have room only to speak of Morton, Davis, E. G. Squier, Pickering, L. H. Morgan, Agassiz, Nott and Gliddon, Wyman, J. D. Whit- ney, Foster, Jones, Abbott, Gatschek, Dorsey, Bessels, Carr, Berendt, Leidy, Baird, Dall, Powell, Putnam, C. A. White, Rau, Gillman, Meigs, Jackson, Barber, C. Thomas, and a number of collectors and students now in the field, chiefly of aboriginal archxology. The third, or evolutional epoch, produced an original and distinctively American school of evolutionists. Hyatt’s memoir On the Parallelism between the Different Stages of Life in the Individual, and those in the Entire Group of the Molluscous Order Tetrabranchiata, was published in 1867, and several papers, extending his views to other groups of Ammonites and molluscs, have appeared since then. Cope’s Origin of Genera was published in 1868, and his paper On the Method of Creation of Organic Types, in 1871. As Cope observes, the law of natural selection “has been epitomized by Spencer as the ‘survival of the fittest.’ This neat expression, no doubt, covers the case; but it leaves the origin of the fittest entirely untouched,” and he accordingly seeks for the causes of its origin. Here also should be men- tioned the writings of Baird, Allen, and Ridgway, on the laws of geographical distribution and climatic variation in mammals and birds, which have revolutionized our nomenclature in these classes, and bear directly on the evolution hypothesis. Special attempts to ascertain the probable ancestry of American mammals have been made by Cope, Marsh, and Gill; of cephalopod molluscs by Hyatt; of insects by Packard; and of brachiopods by Morse. Contributions to the doctrine of natural selection have been made by Dr. W. C. Wells, Rafinesque, Haldeman, Walsh, Riley, Morse, Brooks, and others. The papers by J. A. Ryder on mechanical evolution, and by Hyatt on the influence of gravitation on the animal organism, deserve especial mention, as do Whitman’s on the theory of concrescence. In conclusion we may close this historical sketch with some pertinent remarks of Galton in his work on Hereditary Genius : — “The fact of a person’s name being associated with some one striking scientific discovery helps enormously, but often unduly, to prolong his reputation to after-ages. It is notorious that the same discovery is frequently made simultaneously and quite independently by different persons. Thus, to speak of only a few cases in late years, the discoveries of photography, of electric telegraphy, and of the planet Neptune through theoretical calculations, have all their rival claimants. It would seem that discoveries are usually made when the time is ripe for them — that is to say, when the ideas from which they naturally flow are fermenting in the minds of many men. When apples are ripe, a trifling event suffices to decide which of them shall first drop off its stalk; so a small accident will often determine the scientific man who shall first make and publish a new discovery. There are many persons who have contributed vast numbers of original memoirs, all of them of some, many of great, but none of extraordinary importance. These men have the capacity of making a striking dis- covery, though they had not the luck to do so. Their work is valuable and remains, but the worker is forgotten. Nay, some eminently scientific men have shown their original powers by little more than a continuous flow of helpful suggestions and criticisms, which were individually of too little importance to be remembered in the history of science, but which in their aggregate formed a notable aid toward its progress.” A. 8. Packarp. LOWER INVERTEBRATES. Branco JI.— PROTOZOA. In the pages of the Introduction we have a definition of a cell, with a brief account of the part it plays in the structure of animals, and now in the Protozoa we are to study the manifestations of cell life in their simplest forms; for these animals during their whole existence consist each of but a single cell; yet, simple as this structure would seem to be, we find manifestations of almost all vital phenomena exhibited by these forms. Every member of the branch has the power of motion, of assimilating food, and of reproducing its kind, all of these functions being performed by the single cell. In the Cuvierian system of classification no place was accorded to this group, for they were either regarded as embryonic forms, or, as in the case of the Foraminifera, they were transferred bodily to some of the four great divisions into which the animal kingdom was divided. Though the Protozoa have been studied for over two hundred years, it was not until 1845 that they were first considered as unicellular forms, and for along time after that date the most prominent naturalists refused to accept the con- clusions of the illustrious von Siebold. Ehrenberg, who studied these forms very thoroughly, and in 1838 published a large and extensively illustrated work upon them, describes with great detail nervous, digestive, motory, reproductive and sensory sys- tems in these really simple organisms, all of which have since been shown to have no actual existence. These mistakes, great as they now appear, arose very naturally, for at the time at which Ehrenberg wrote, Schwann had not made known his studies upon cells; and highly preposterous at that day would seem the idea that an animal could exist without definite organs to perform the functions of animal life. Were space at our disposal, it would prove an interesting chapter to review the history of the disputes regarding the character of these forms, the rash and dogmatic assertions of prominent naturalists who believed that there could be only the four great divisions of the animal kingdom which the great Cuvier had proposed, and, on the other hand, the patient observations and the guarded statements of their opponents. Time, however, served to clear up the doubts surrounding these minute forms, and to-day not a naturalist lives who does not in some way accept the group. The Protozoa are mostly microscopic animals consisting of but a single cell, or, in a few cases, apparently of an association of cells, without, however, any differentiation into tissues. These few apparent exceptions will be considered more at length further on. In some of the Protozoa the cell is provided with a nucleus and various other differentiations of the protoplasm ; in others no such structures have as yet been dis- covered, the animal, so far as our knowledge enables us to say, being but a cytode, a voL, I.—1 2 LOWER INVERTEBRATES. mass of protoplasm capable of taking food and reproducing its kind. Concerning these latter our knowledge is not absolute, and further observation may show that in these a nucleus really exists, a result rendered more probable by the fact that in the Forami- nifera, in which the existence of a nucleus was long denied, that specialization of the protoplasm has recently been discovered. Another feature which frequently occurs in the Protozoa is the contractile vacuole. This is as yet a problematic arrangement, the function of which cannot be said to be decided. There appears in the body a clear vesicle which, sometimes spherical, sometimes irregular and ramified, slowly increases in size, and then suddenly contracts, leaving no trace, and then gradually appears again, only to repeat the operation. It is thought that in some cases these contractile vacu- oles communicate with the exterior, but this has not been proved. In short, there remains a fine field for investigation in the structure and functions of these problem- atical organs, which will be described more in detail in the succeeding pages. Food is taken by the Protozoa into the interior of the body, the digestible portions assimilated, and the portions of no use to the organism afterward rejected. In the lower forms all parts of the body seem to be equally adapted for the capture and engulfment of food, the Protozoan simply crawling around the object; while in the higher there is a distinct portion of the cell set apart for the introsusception of nutri- ment. The character of nourishment also varies, some forms living on vegetable pro- ductions alone, while others absorb any organic bodies, animal or plant, often devouring forms, rotifers, worms or crustacea, far higher in the scale than themselves. In the higher Protozoa the food is either brought to the part of the body set aside for the reception of food by currents of water created by rapidly moving cilia, while in others the animals which are eaten are in some unexplained manner benumbed by the Proto- zoan and then devoured. When taken into the body the aliment forms a mass slowly circulating through the protoplasm and is known as a food vacuole. Reproduction is accomplished in several distinct ways; by fission, by budding, by encystment, and the subsequent formation of young, in which the act of conjugation frequently plays a part not yet understood. Two and sometimes more individuals unite and form a single mass, and then either separate, or the whole becomes encysted ; but whether this is to be regarded as a true sexual act, or as an obscure something not clearly defined by the term applied to it of “rejuvenescence,” has not been settled. Four well-marked groups of Protozoa occur; Monera, Gregarinida, Rhizopoda, and Infusoria. The great German naturalist Heckel has proposed a third division, Pro- tista, of organized beings to contain forms which cannot be certainly classed with either the animal or the vegetable kingdoms, and here would come the group Monera, together with other clearly closely allied groups which, by common consent rather than by definite character, are usually regarded as belonging to the vegetable kingdom. But though hard and fast lines do not exist in nature, we are compelled to create boun- daries which are frequently as arbitrary as any to be found in geographies, and for the purposes of this series we prefer to consider the Monera as belonging to the animal kingdom, and to ignore the claims of the Protista. Cuass I.—MONERA. Tue Monera, the lowest group of the Protozoa, may be briefly described, following partly the language of Heckel, as follows : — MONERA. 8 Organisms without organs. The entire body consists of nothing more than a bit of plasma or primitive jelly, an albumenoid compound not differentiated into proto- plasm and nucleus. Every Moner is therefore a cytode but not a cell. Their form is indefinite, with lobes or pseudopodia projecting from any part, by means of which they move. They multiply by division, budding, or by the formation of spores, as will be described further on. They live mostly in water. The manner in which the Monera envelop and flow around their food shows the absence of a definite limiting membrane or cell-wall, and also the extreme simplicity and homogeneous character of their body substance ; since any portion of it surrounding a particle of food causes digestion and assimilation to take place. This method of securing food will be more fully described when treating of the Amaba. The reproductive processes are rather more complex than would be anticipated among such low forms of life. The simplest method of propa- gation is by division of the or- ganism into two parts by a construction across the middle, forming two animals precisely like the parent form. The Protomyxa auranti- aca represented in Fig. 1, is a typical Moner. It is shown at (J) in its active, creeping con- dition, the pseudopodia stream- ing outward in all directions with clear spaces or vacuoles and food particles in the in- terior. The food is entangled in the reticulate pseudopodia and gradually drawn into the body, where a temporary stom- ach is formed by the surround- ing protoplasm. After the di- gestible portions are absorbed the rest is cast off from any part of the surface. This Moner multiplies by the for- mation of swimming spores in this manner: The pseudopodia are all retracted and the Moner Fig. 1.— Protomyxa auriantiaca; a. encysted; b. division of proto- becomes sp herical (2) . Itthen piem $205 ag bureGing | sie rise a the eer d. os — _ which, by coalescence, the feeding plasmodium, /. is formed. becomes encysted by the for pe heel afr mation of a thick outer mem- brane, meanwhile changing to an orange-red color. The cyst ripens by the sub- division of the contents (b), and finally the enclosing membrane ruptures (c), and the contents escape as bright red, active swarm-spores, which swim about by the aid of the delicate, lashing flagella or threadlike extensions of the protoplasmic body. These changes are illustrated in the figure a, b, c, and d, being the successive stages 4 LOWER INVERTEBRATES. from cyst to swarm-spores, and ¢ being the first stage of reversion from swarm-spores to the mature form. The swarm-spores, to which the name plastidules has been given, are masses of apparently structureless protoplasm, manifesting life in its simplest conceivable form. Crass IIT.— RHIZOPODA. No definite boundary can be drawn between the Monera and the Rhizopoda, and it is doubtful if the simple Protomyaxa just described as a typical Moner, does not justly deserve to rank in this class. In a general way it may be said that the Rhizopods are distinguished from the Moners by having a more or less well-defined outer layer of sar- code and a nucleus, although the latter is not always to be observed. The Rhizopoda have been divided by Dr. William B. Carpenter into three groups, distinguished by the character of their sarcode or pseudopodia; the Lobosa, in which the pseudopodia are lobose or finger-like, as shown in the illustration of Amcba pro- teus, Fig. 2; the Radiolaria, in which the sarcode extends outward in rays more or less constant in form and position, as in * FIG. 9. ie ovodimare, greatly enlarged, OFSanisms were obtained by Mr. Murray RHIZOPODA. 18 ‘OrnpER III.— HELIOZOA. The Heliozoa, or sun-animalcules, are very beautiful Rhizopods, inhabiting fresh water. Most of them are spherical, floating forms, but a few are attached by long pedestals or stipes. The pseudopodia are in the form of delicate, tapering rays, extend- ing outward in all directions from the centre, often exceeding the diameter of the body in length. They are flexible, more or less contractile, and sometimes reveal a slow circulation of granules along their length. The sarcode is not distinctly differentiated into endosarc and ec- tosare, but in one interesting form, Actinospherium, the outer sarcode is a frothy, vacuolated mass of consider- able thickness. The most common of the Heliozoa is the Actinosphrys sol. It is found in pools of standing water almost every- where, among the floating plants, ap- pearing under a low-power of the microscope as a colorless, spherical body, varying in size from .04 mm. to 12 mm. in diameter, with innumer- able delicate, bristling spines three or four times the diameter of the body in length. The sarcode is full of vac- uoles, which give it a frothy appear- ance. Watching the minute sphere a few moments, there will probably be seen somewhere along the periphery a slowly distending vesicle, which reaches a certain size, and then suddenly col- lapses. This is the contractile vesicle. The first description of this curious. little creature seems to have been given by a French naturalist, who referred to it, if we may translate the bad French in which it is written, with some dis- cretion — as “a fish, the most extra- ordinary that one could see.” The food of Actinophrys consists F1a, 10. — Clathrulina elegans, enlarged 350 times. of minute infusoria, diatoms, and other unicellular alge, which frequently can be seen within the body as green balls. The pseudopodal rays are used as organs of locomotion, and for the prehension of food. If an active infusorian comes in contact with the spines it seems to be paralyzed. If the prey be very minute it will be seen to glide along the rays very gradually until it reaches the body, when a portion of the sarcode is projected to envelop it, and draw it into the 14 LOWER-INVERTEBRATES. interior, where it undergoes digestion and assimilation. If the prey be larger, several rays may bend toward it and together secure and draw it down to the body. Actinophrys propagates by simple division and by the fusing together of two or more specimens into a single mass, which then reproduces new forms by fission. The conjugation of two individuals is quite a common occurrence, but the Hon. J. D. Cox has observed as many as nine individuals joined in the process. The same observer also describes another method of propagation in which the parent form passes into an opalescent condition, after which it undergoes segmentation into a brood of young. A much larger heliozoon, greatly resembling Actinophrys, is Actinospherium. It is especially distinguished from the former by the frothy layer of ectosare which sur- rounds the central sarcode, and by the complex structure of the pseudopodal rays which, under high magnification, seem to have a hard axis-cylinder, probably only a core of denser protoplasm. Perhaps one of the most beautiful forms of this order is Clathrulina, represented in Fig. 10. While young the capsules are colorless and clear, but with age they be- come yellow. The sarcode does not usually fill the lattice-capsule, but is collected in a ball within it. It isa very beautiful species; often found in great abundance in ponds and ditches. The Heliozoa seem to be quite closely related to the Radiolaria, but the exact rela- tions of the two groups is not yet known. It has been suggested that the Heliozoa are embryonic forms of the more highly-developed group; but until the structure of both groups is more fully elucidated it seems useless to speculate much about this question. Several observers have noticed within Actinophrys a peculiar nuclear sphere which greatly resembles the central vesicle of certain Radiolaria. OrverR IV.—RETICULARIA. SUB-ORDER J. — PROTOPLASTA. This sub-order includes a considerable number of fresh-water Rhizopods with very soft sarcode bodies and delicate, branching, thread-like pseudopodia. The endosarc and ectosare are even less clearly differentiated than in the lobose forms. The nucleus is usually large, and several contractile vesicles are to be seen in the endosarc. A characteristic Rhizopod of this sub-order is Gromia oviformis, represented in Fig. 11. The shell is thin, chitinous, colorless or yellowish, measuring about .115 mm. in length. A high power of the microscope shows an incessant streaming of granules along the branching, anastomosing shreds of sarcode, the granules moving outward on one side and back on the other side of each filament. The sarcode extensions of Gromia anastomose more freely than is usual among the Protoplasta Filosa, resembling more closely the Foraminifera in this respect, and the contractile vesicle is near the mouth of the shell. In fact, Prof. Joseph Leidy, in his monograph on the “ Fresh-water Rhizopods of North America,” has placed Gromia among the Foraminifera. The filose protoplasts seem to be in nowise different from the Foraminifera, except that the shells of the latter are usually calcareous, and the pseudopodia manifest a greater tendency to anastomose, and are more granular. The shells of the filose protoplasts are usually composed of a clear, chitinous sub- RHIZOPODA. 15 ‘stance, sometimes colorless and transparent, sometimes distinctly colored yellowish or brown, while still others are covered with grains of sand. A very frequently occurring form is Pseudodiffiugia. In this the shell is chitinous, with sand- grains in some wise incorporated with it. It resembles Diffugia, Fig. 8, in every respect except as regards the character of the pseudo- podia. In some of the genera the shells are beautifully marked, and the neck is often curved so that the body lies on the side as the animal crawls along. SUB-ORDER II. — FoRAMINI- FERA. The Foraminifera embraces an almost innumerable variety of ma- rine Rhizopods. The reticulate, anastomosing nature of the pseudo- podia is most strikingly manifest in all the Foraminifera, but the ex- amination of the internal sarcode is very difficult, owing to the thick- ness and opacity of the shells. For this reason it was long supposed that the Foraminifera were desti- tute of a nucleus, but recent inves- tigations by Hertwig and Lesser, Carpenter and others, have revealed nuclei in several forms, and they are doubtless present in all of them. It is said that dahlia violet will stain the nuclei while the animal lives, and if this is true in all cases, it will prove a valuable reagent in further in- vestigations of those organisms. The Foraminifera are the only Rhizopods that have shells of many chambers, and of complex structure. The different forms of the shells can best be understood by observing how they are derived from a single chamber by the budding off of successive portions of the sarcode-body, each of which then secretes a shelly covering. If the budding always takes place in the same direction, an elongated form composed of several chambers in a straight line is produced, as in Lagena. If the tendency of growth is to produce a spiral, it results in the beautiful Cornuspira, which greatly resembles the mollusc Planorbis, or, if the budding takes place in still another way, the more complex forms of Miliola are produced, which are only spirals greatly elongated in one direction. Instead of forming successive single chambers at the ends of old ones; the growing spiral may spread out wide and flat, thus forming the beauti- Fia@. 11.— Gromia oviformis, enlarged 600 times. 16 LOWER INVERTEBRATES. ful Polystomella, and Peneropolis, Fig. 12, common in all tropical seas. In the Ber- muda sands the most frequently occurring genera are Peneropolis, Fig. 12, Orbiew lina, and Orbitolites, Fig. 15. These, with other light débris, are occasionally washed out of the heavier matters of the shore by the action of the waves, and left in great abundance in Z white streaks as the waves recede. Among the spiral shells there are two types, distin- guished as nautiloid and turbinoid. When the spiral forms in one plain, as in Polystomella, we have a nautiloid spiral ; when it winds obliquely around a vertical axis, forming a spiral like the snail or periwinkle, it is turbinoid. The beautiful Rotalia, Fig. 18, is formed upon the latter plan. In most of the rotaline forms, all the chambers of the whorl are visible from one side, but among the spirals of the nautiloid type the later chambers often more or less en- velop the older ones, so that unless one knows the struc- ture of the shell it cannot be recognized by a cursory or superficial examination. For example, in the very frequently occurring Monionina, the older chambers are quite invisible, being entirely enveloped by the Jater ones, and in order to learn how the shell began to form, a section would have to be made through it showing all the chambers in one plane. Among the turbinoid spirals, there are several varieties of structure, the relations of which are not easily seen until careful examination of the in- Fie ternal structure reveals them. Thus, Textularia, Fig. 14, belongs to the division, but at first glance it scarcely seems to bear any relation to WVontonina. On close examination it will be seen that the successive chambers are in two rows, and each chamber communicates with the chamber above and the one below it on the other row, hever opening into a chamber of its own row. In some species the nautiloid spire is characteristic only of the early period of growth, for after a few turns, instead of budding from the end, thus continuing the spiral, all the outer chambers put forth radial buds, which form successive concentric rings. This mode of growth is well illustrated in Orbitolites, which is represented in € Fig. 15, part of the surface being removed to show the internal struc- ture. It will be seen that the internal chambers are spirally arranged, while the others are arranged on the cyclical or radial plan of growth. Dr. William B. Carpenter, whose valuable monograph on the Fora- minifera has thrown much light upon the structure and relationship of these organisms, has shown the great importance of a careful study of the shell-structure as a basis of classification. He has distinguished two y kinds of shell among the Foraminifera, which he has designated, re- spectively, the porcellanous and the hyaline, or vitreous. These differ- Fi¢.14.—Tectu- ences of shell-structure correspond with physiological differences in the eae organisms inhabiting the shells, and afford a basis for a division of the class into two great sections. : In both these sections will be found species which have striking resemblances in form, which could not be generically separated except by a recognition of the differences in the structure of the shell and their physiological significance. a sy” iy Fic, 12. Ries enlarged. Fic. 13. — Rotalia, enlarged. ube ff hol Bey aol Poy Ys Wifi) th Polystomella strigillata, a foraminifer with pseudopodia extended, enlarged 200 times. ng RHIZOPODA. 17 The terms porcellanous and vitreous have been adopted owing to the appear- ance of the shells as seen under the microscope. The former is applied to shells of a white, opaque, often shiny appearance, which in thin, transparent sections or lamin appear, by transmitted light, of a brown or amber color. No structure can be observed in shells of this kind. They are never perforated, although they are sometimes marked upon the surface with pits, or inequalities, giving an appearance of foramina. The vitreous or hyaline shell-structure is far more complex than the porcel- lanous. It is transparent, usually colorless, sometimes deeply colored, and more or less closely perforated either with large or small distinct foramina, or minute tubuli passing directly through the shell-substance. In Rotalia, Fig. 18, the foramina are distinct, and afford passages for the sarcode, which covers the outside of the shell, and the pseudopodia extending in all directions from it. The minutely tubular structure can only be detected in thin sections with high powers of the microscope, when it imparts a peculiar appearance to the shell, characteristic of finely tubular structures. Between the shells with large foramina and with minutely tubular structure, there is a continuous gradation, which indicates that both foramina and tubuli subserve the same pur- pose, — affording channels for the passage of the sarcode. Comparing the shells of the porcellanous and vitreous forms, it will be seen that while the | pseudopodia of the animals oc- cupying the former all spring from the terminal or outer chambers alone, so that the nourishment for the sarcode of the inner chambers must pass in through those that in- : tervene, in the vitreous forms Fie. 15.— Cen Se nears soa ehow external appear- the sarcode of each chamber is in direct communication with the outer world through either the foramina or the minute tubuli of the shell. In accordance with this difference in the structure of the shell-substance, it may be also observed that the stolons of sarcode connecting successive chambers of the porcellanous-shelled species are much larger than those in the vitreous-shelled forms. These facts may be best illustrated by comparing two of the most highly-developed forms of the two types of shell-structure. For this purpose we will select Orbitolites of the porcellanous, and Nummulina among the tubular-shelled forms. The structure of Orditolites can be understood by a glance at Fig. 15. Disks such as are here represented sometimes attain the size of a silver quarter-dollar in diameter. It will be seen that single pores unite successive chambers, and finally the sarcode of the outer chambers communicates with the surrounding medium by pseudopodia pro- jected through the marginal pores shown in the figure. In Nummulina, a form that has been so abundant in the past as to have lent its VOL, I. —2 18 LOWER INVERTEBRATES. name to the nummulitic limestone, the tubes have a different arrangement and are very minute; there is, besides the tubular structure already described, a system of inoseulating canals penetrating the septa, which are filled with sarcode during the life of the animal. In all the vitreous forms, each chamber has its own shelly in- vestment, so that the partitions between the chambers are double. Between these walls there is frequently a considerable deposit of calcareous substance, which is known as the intermediate skeleton. Through the intermediate skeleton runs the system of canals, which is beautifully shown in Hozoon, soon to be described; the canal-system resembling minute branching shrubs. A single species of NMummu- Fié. 16.— Nummulina wilcoxi, natural size, lina, Fig. 16, has been described from Florida. and enlarged. Besides the two varieties of shell-structure above described, there is another kind of shell or test very frequently occurring among deep- water species. This is the arenaceous type, in which the shell consists of cemented grains of sand, or of sand and spicules together. The nature of the cement which holds together the sand-grains of the arenaceous types is not known; sometimes the grains are only loosely united, so that the test is more or less flexible, as in Astrorhiza, Fig. 17, a form which is found in Vineyard Sound at depths of only twelve fathoms, but also reaching down to over five hundred fathoms. Some of these have the outside test smoothly plastered by a layer of very fine particles of mud, although composed of irregular large and small grains of sand. No definite aperture, or mouth, has been observed in Astrorhiza, and the sarcode finds its way through the test between the loosely 5 cemented grains composing it. In other forms the grains are very closely cemented, so that some tests will resist the action of warm nitric acid, proving that the cement is neither calcareous or ferruginous. In some cases the sand-grains seem to have a chitinous basis in which they are imbedded. The resemblance between the arenaceous Foraminifera and the porcellanous and vitreous species is striking. Take, for example, Halophrag- ** ‘ mium, and compare it with Globigerina, Fig. 18. % Indeed, it is true that if we consider only the external forms, ne we can find in the three divisions of porcellanous, vitreous, and arenaceous forms many species that are so closely related as to be indistinguishable by any specific characteristics. Thus, Cornuspira among the porcellanous is the counter-part of Spirillina among the vitreous forms; and this is distinguishable in form from Ammodiscus among those with sandy tests. While some of the tests of the arenaceous group are probably imperforate, others are, without doubt, more or less porous, so that the distinction already made between hyaline and porcellanous forms must also hold good as concerns these. Indeed, cer- tain arenaceous forms have no definite mouth, and the sarcode must find its way through pores in the test. The deep-sea investigations that have been carried on of late years have brought to light many new forms belonging to genera which were supposed to be very well known. Thus, the shell of Globigerina, Fig, 18, has been understood, conforming to the descrip- tion of Dr. Carpenter, to consist of a series of hyaline, perforated, spheroidal chambers arranged in a spiral about an axis, each opening into a central space in such a manner RHIZOPODA. 19 that all the apertures are visible when looking into the common vestibule. But in the light of more recent investigations, Mr. Brady has found it desirable to enlarge the scope of the family to include many new species. He has, therefore, divided the Fig. 18. — Globigerina bulloides, greatly enlarged. Globigerine into three groups, according to the position and appearance of the aper- tures, as follows: — 1. Forms with an excavated cavity (umbilical vestibule) into which the orifices of all the segments open, such as Globigerina bulloides, Fig. 18. 2. Those with only one external orifice, situated on the face of the terminal segment, at its point of junction with the previous convolution, as in Globigerina inflata. 20 LOWER INVERTEBRATES. 3. Forms in which the inferior aperture is single and relatively small, but supple- mented by conspicuous orifices on the superior surface of the shell, as in Glodigerina rubra, Besides these, there are forms represented under the generic name Orbulina, which seem properly to belong to the Globigerine as sub-generic forms. Orbulina has a spherical shell, usually without a definite mouth, but provided with two sets of perfo- rations differing in size, — one series numerous and minute, the other larger and less numerous. Closely allied to the Globigerina, if not properly belonging to that family, is the beautiful Hastigerina murrayana, found by the “Challenger” expedition. This organ- ism was found long ago by D’Orbigny (1839), and described by him as Monionina pélagica, and was one of the first Foraminifera taken at the surface of the sea. The Foraminifera inhabit the sea, and their remains are gradually forming rocky strata on the ocean-bed, in all respects like the chalk of the cretaceous period. For a long time it was supposed that the Foraminifera found at the bottom of the sea passed their entire life there. Prof. Wyville Thomson held firmly to that opinion until the results of collections with the tow-net at the surface conclusively proved that many of them live near the surface. It is now known that a few species of Globigerina inhabit the superficial waters, but a far greater number pass their life at the bottom. The pelagic forms of Globigerina are usually, but not always, spinous. The long, delicate spines are somewhat flexible, and clothed with granular streaming sarcode; and for some distance from the shell the frothy sarcode fills the spaces between them. The spines are so delicate that a mere touch will break them off, and spinous shells are never seen in material brought up in the dredge. Sometimes the spines are very long; in Hastigerina murrayi the spines are fifteen times the diameter of the shell, and the frothy, alveolar sarcode extends outward between the spines to a distance equal to twice the diameter of the shell. The Globigerina are so abundant in some places, and their remains constitute so large a proportion of the shiny calcareous ooze covering a great part of the sea-bottom, that the ooze has long been designated “Globigerina ooze.” The Globigerina ooze consists of the remains of Glodigerina and Orbulina in great abundance, with a smaller proportion of the genera Pullenia and Spheerodina, with occasional specimens of Has- tigerina, together with remains of radiolarians, diatoms, and some curious structures known as rhabdoliths and coccoliths, the nature of which is not yet understood. As regards the distribution of the remains of protozoic life over the ocean-floor, it appears that the Globigerina ooze extends from four hundred down to about two thou- sand fathoms. Beyond this limit there seems to be a gradual disintegration and solution of the calcareous substance of the shells, resulting first in a gray ooze down to two thou- sand three hundred fathoms, containing no perfect shells, but some calcareous matter effervescing with acids, finally changing as we go still deeper to an impalpable red feldspathic mud, or “red clay,” as it has been termed, which covers vast areas. The red clay is supposed to be derived partly from the disintegration of the shell-matter of the gray ooze and the solution of the calcareous portions, and partly from the mineral Fig. 19.— Helixostegine forms of Foraminifera. RHIZOPODA. 21 matter held in suspension in the sea-water, which slowly sinks to the undisturbed depths. i Nevertheless, the deepest ocean-floor is not always devoid of organic remains. The deepest sounding by the “Challenger” was made in the Pacific Ocean on the 23d of March, 1875, and showed a depth of four thousand five hundred and seventy-five fathoms. The bottom was covered with what resembled the ordinary red clay to the eye, but it was gritty, and contained such a large proportion of radiolarian remains that it received the name of Radiolarian ooze. It had previously been supposed that even these silicious remains, together with the frustules of diatoms, which are more or less abundant in the Globigerina ooze, disappeared with the calcareous shells, in some manner not fully understood. The occurrence of the deep Radiolarian ooze, however, has shown that there is no destruction of silicious shells, and their accumulation in so much greater abundance there than in the Globigerina ooze was accounted for by Prof. Wyville Thomson on the supposition, based upon the results of collections at different depths down to one thousand fathoms with the tow-net, — that Radiolaria lived at all depths, and therefore, where the water was deepest the accumulations of their skele- tons would be the most rapid. Later investigations by Mr. Agassiz, using an ingenious apparatus devised by Lieut~Commander Sigsbee, U.S. N., have shown that there is no life between a narrow zone where the surface animals are found and the habitat of those living on or very near the bottom. The deepest cast that has ever been made was made from the U. 8. Coast Survey Steamer “Blake” in January, 1883, in latitude 19° 39’ 10” N., and longitude 66° 26, 05" W., between the Bermudas and the Bahamas, about one hundred miles N. W. of St. Thomas. The depth there found was four thousand five hundred and sixty-one fathoms; the temperature of the deepest water was 86° F. Another cast in latitude 19° 29’ 30" N., longitude 66° 11’ 45”, showed a depth of four thousand two hundred and twenty-three fathoms. At these great depths, — more than five statute miles beneath the surface, a depth equal to the height of the highest mountains in the world —the bot- tom is covered with a very fine brown ooze, containing a few Diatoms and sponge spicules. In the North Pacific, at depths of three thousand and four thousand fathoms, are found tests of Zrochammina (Ammodiscus) incerta, one of the arenaceous forms. At great depths are also found species of Mfliola, usually more or less incrusted with grains of sand, while in some cases the shell consists not of lime, but of clear, homo- geneous silica which will resist the action of acids like the frustules of diatoms. Some of the genera of Foraminifera have had a great range in geologic time. In the lower Silurian rocks of Russia—in the so-called Ungulite grit— Ehrenberg found green sand casts of genera now living, Textularia, Gattulina, and Rotalia. The oldest form of life of which the rocky strata furnish any remains is possibly the Hozoon Canadense, found preserved in greatest perfection in the Laurentian rocks of Canada. Concerning the nature of Hozoon —the dawn-animal — there has been much contro- versy. On the one hand it is claimed with great probability that the peculiar struc- tures found in the rocks are of purely mineral origin. But Dr. J. W. Dawson and Dr. William B. Carpenter, who have studied this subject with great care, have declared that the structure of Hozoon corresponds in every particular with that of cer- tain Foraminifera of the vitreous type. The successive chambers connected by pas- sages, the intermediate skeleton with its complex system of inosculating canals, the minutely tubular “nummuline layer,” have all been claimed to have been found and 22 LOWER INVERTEBRATES. studied with great care. The Hozoon occurs in a serpentine limestone, in the form of irregular masses of varying size up to several inches in diameter. In appearance to the naked eye it consists of alternate bands of green serpentine — a silicate of magnesia — and limestone, the former filling the cavities originally occupied by the sarcode, and even the most minute tubuli of the nummuline layer; while the calcareous basis of the original skeleton remains unchanged. The simplest, and on the whole the most satisfactory, method of studying the Fozoon is to cut tolerably thin slices of the rock and place them in a very dilute acid until the calcareous portion is dissolved. There then remains a perfect cast of the chambers of the shell, counterparts of the original sarcode-body, even to the minute tubules of the nummuline layer. We have given here the gist of the account of Drs. Dawson and Carpenter, but the question of the animal nature of Zozoon is far from settled ; possibly it never will be. In South Carolina there are immense beds of marl and limestone containing For- minifera in great abundance. Prof. J. W. Bailey, in the year 1845, examined some borings from a well driven through these deposits at Charleston, and also some frag- ments from an outcrop on Cooper River, about thirty-five miles above that place. From the borings it was observed that from one hundred and ten to more than three hundred feet in depth the Polythalmia were abundant, very perfectly preserved, and many of them large enough to be easily seen with a pocket-lens. Concerning these tertiary deposits, Prof. Bailey remarked that they were filled with more numerous and more perfect specimens of these beautiful forms than he had ever seen in chalk or marl from any other locality. Similar marls are also found in Virginia, on Pamunkey River, belonging to the eocene; and in the miocene rocks of Petersburg, Foraminifera are also found. The foraminiferal rock which underlies so large a part of South Carolina is still in process of formation along the coast. The mud from Charleston harbor abounds in shells of Foraminifera, and the remains of diatoms. Fossil Foraminifera are found in many other places in this country. They exist in New Jersey, Alabama, at various points on the Missouri and Mississippi rivers, in Ten- nessee, Arkansas, North Carolina, Florida, and elsewhere. The marls of certain localities along the upper Missouri and Mississippi rivers are very rich in Foraminifera. The latter deposit is popularly known as “prairie chalk,” and the forms are different from those found on the Missouri. In the green sands of Fort Washington, Va., Prof. Bailey made the remarkable discovery that these minute and perishable organisms could be entirely destroyed by chemical changes, yet leave indestructible memorials of their existence in the form of mineral casts. Ehrenberg had previously observed that the lime of the shells could be gradually dissolved and replaced by silica. In flints such a replacement is not un- usual, and remains of shells thus mineralized can be obtained by treating the rock with acid, which leaves the silicified shells intact. But in the green sands of the chalk formation in New Jersey, Virginia, and else- where, the shells have become filled with a greenish mineral, glauconite, — a silicate of iron and potash of varying composition — which has followed every contour of the shell, and penetrated even the minute pores and tubuli so perfectly that the genus and even the species of the Foraminifera can be readily determined by a study of the glau- conite casts after the shell has been destroyed. The glauconite occurs in grains scattered through the green sand formation of the GREGARINIDA. 93 cretaceous and other periods. In many cases the grains are found to be casts of Fora- minifera. These constitute as much as ninety per cent. of some rocks. In the yellowish limestone of Alabama such casts occur in great perfection, constituting about one-third of the rock. To obtain them, the stone has only to be treated with acid, when the greenish casts can readily be picked out from the insoluble residue, consisting of sand and finely-divided mineral particles. Ehrenberg was the first to observe the replacement of organic forms by mineral matter, and he inferred that green sand was always formed by such a substitution. Such casts can be found in limestones from Mullica Hill, and near Mount Holly, N. J., from Drayton Hill, near Charleston, 8. C., from the cretaceous rocks of Western Texas, and from other localities. At the present time precisely similar casts of Foraminifera are being formed at the bottom of the sea. In the year 1853 Count Pourtales found, off the coast of Georgia, in the Gulf Stream, at a depth of one hundred and fifty fathoms, a bottom deposit consisting of shells of Globigerina and black sand in about equal proportions. Similar deposits were found also in the Gulf of Mexico and in various parts of the Gulf Stream. With them are also found the living Foraminifera, so that there can be no question as to the continuance of the process now. Romyn Hircucocx. Cuass III. — GREGARINIDA. The Gregarinida are a peculiar kind of animal parasites which inhabit the intestinal canals of earthworms, insects, crustacea, etc., the simplicity of whose structure leads most authors to class them among the Protozoa. Their distinct mem- branous investment, however, entitles them to a higher rank than any of the Protozoa already described, and, although with very little power of movement, and possessing no means of searching for and collecting food, they are still structurally higher than the Ameba and its allies, for a differentiation of parts is certainly distinctly shown in the mem- branous cell-covering. As parasites they do not require to move about in search of food. They have no mouth, no organs of digestion. They absorb their food through the membrane that covers the body; hence, although they are structurally above the Ameeba, they have almost lost the Ameba’s power of voluntary movement. We may conceive of an Ameba placed under conditions that would insure an abundant supply ; 3 . * « e « Fig. 20. — Clepsi- of food without the necessity of searching for it, finally losing its power ~ “arina muneri, of movement and developing a distinct membranous investment from — °!"8°4- the ectosare. We would then have a Gregarine. Van Beneden has regarded the Gregarinida as Amcebe thus degenerated by parasitism. But there has been no degen- eration of structure, only of habit; it will be seen that Gregarines are all amceboid in one stage of their development, and that from this larval condition the more highly differentiated adult is produced. The Gregarinida vary considerably in form and appearance, but in general terms they may be described as more or less ovate or cylindrical in form, the body consisting 24 LOWER INVERTEBRATES. of a single cell frequently divided into two or more portions by transverse, internal septa, forming the anterior and posterior sacs. In some species the anterior end, or head, is furnished with a circle of reflexed hooklets, in others no such armature is found. The membrane covering the body is transparent and structureless in appearance. Although firm and elastic, it is very permeable to watery fluids. The contents of the body are a nucleus embedded in the protoplasm and fatty granules. The latter are usually so abundant as to give a milky appearance to the cell contents. The granules seem to increase in size and abundance as the animal matures, since in young individ- uals they are scarcely noticeable. The nucleus invariably present in all Gregarines is a spherical vesicle with a sharply- defined membrane, situated near the middle of the cell in the Monocystidea and in the forward part of the posterior sac of the Dycistidea. A nucleolus is usually found within it. When about to multiply, the Gregarine become surrounded by a transparent coat or cyst, which may include either a single specimen or two together. After becoming encysted a change takes place in the enclosed Gregarines. If two of them are in the cyst they become united, lose their identity and merge into a single mass. From this mass nucleated cells soon develop, which gradually take the form of elongated bodies, tapering at both ends, greatly resembling certain diatoms known as Wavicula, whence they have taken their name, pseudo-navicule. They are also known as psorosperms. Finally the membrane of the cyst is ruptured and the pseudo-navicule escape. The process above described is not the only one by which the spores are formed, even in the same species. At least two others are known, one a process resembling the segmentation of an egg, in which the entire mass is converted into very regular and granular spheres of segmentation, which in turn becomes elongate and covered with a firm investment, while their contents become more fluid; another in which the con- tents, instead of producing granular spheres, divides into two, four, or more parts, each of which, by a process not understood, becomes covered with a layer of transparent or slightly granular globules, and these parts are transformed into the spores. In some instances the cysts of Gregarines have been observed arranged in a linear series in the walls of the rectum of certain animals, and it was for a long time a great mystery how they could be thus regularly placed. Van Beneden observed in the rec- tum of a lobster as many as seven cysts in a linear series. The Gregarine of the lobster, Porospora gigantea, attains the extraordinary length of 16 mm. and .15 mm. in diame- ter. During the proper season, spring and summer, it is very abundant in the intestine of the lobster — at least in lobsters from certain localities as many as twenty-five - being sometimes found in a single individual. At this time no cysts can be found, but in the autumn the parasites seem to pass down into the rectum, where they become encysted. The general process of encystment is somewhat as follows: — The contents of the cyst are always at first granular, forming a single sphere with- out anucleus. By division, two rounded masses next appear, and as the diameter of the cyst increases, these separate, and a clear, colorless liquid surrounds them. The wall of the original cyst then, at least in P. yigantea, becomes granular and disappears, while the two globes become surrounded by firm membranes, and their contents may again divide like the parent cyst. In other words, the cysts are capable of multiplica- tion by division through successive generations. It is by the multiplication of the cysts that their linear arrangement is brought about. Eventually the cysts cease to divide, GREGARINIDA. 25 and pseudo-navicule are then produced. We have now to follow the development of new generations from these spores. The development of the pseudo-naviculz has not been fully made out, except in a few cases. It is probable, however, that their granular contents escape, and form ameeboid masses from which the Gregarines are either directly or indirectly developed. In the intestine of the lobster naked protoplasmic masses have been observed, which, as will be seen, have been proved to belong to the Gregarines. In the perivis- ceral cavity of the earthworm the encysted Gregarines, Gregarina lumbricus, are often found in great abundance. There the pseudo-navicule are set free in innumerable quantities, and their contents have been observed to produce ameboid bodies from which new generations of parasites originate. The Gregarine of the lobster, P. gigantea, according to E. Van Beneden, develops from an ameeboid form, but the course of delevopment differs somewhat from that observed in the case of the Gregarine of the earthworm. Within the intestine of the lobster the minutely granular amceboid form from which the parasite develops was found destitute of both nucleus and membrane, resembling Protamcba primitiva, or P. agilis, Haeckel, but not projecting true pseudopodia. These ameboids become converted into spherical, motionless globules, the “generative cytodes,” which finally develop two projecting processes, resembling the stalk of Moctiluca, from which the Gregarines are directly developed. One of the prolongations is longer than the other. The longer one separates from the cytode and then moves about independently, like a nematode worm. The shorter arm then develops, appropriating the entire substance of the cytode, and likewise acquires the form of a nematode worm. These the author has designated “pseudo-filarie.” After some changes in form they cease to move, a nucleolus and then a nucleus forms about the middle of the body, and finally a new Gregarine is developed directly from them. In the development of the Gregarinida we find a complete genealogical, phylo- genetic history of the cell. From the psorosperms are derived plasmic bodies, devoid of nucleus or external envelope, allied to the plastidules of the Monera, already described on page 3, naked cytodes, which are the lowest and simplest forms of living matter. Then a denser layer of sarcode is formed, corresponding to the ectosare of rhizopods, but still there is no nucleus. Soon a nucleus and nucleolus is differentiated from the proto- plasm, and the cytode becomes a perfect cell. This transformation may take place directly, or, as in the case of Psorosperma gigantea, by the budding of the cytode and the development of nuclei within the separated buds. The cycle is completed by the growth of the young Gregarine, its encystment, and finally the production of the psoro- sperms. The Gregarine are divided into two divisions, Monocystidea and Dicystidea, accord- ing as the body is composed of one or two sacs. Schneider, who has given the most complete account of these forms, recognizes eighteen genera of Gregarinz, represented by about thirty species. Our American forms have been scarcely touched, Dr. Leidy alone having investigated them. Romyn Hircucock. * 26 LOWER INVERTEBRATES. Crass TV. — INFUSORIA. The Infusoria are the highest of the Protozoa. They are so regarded because they usually have a definite shape, owing to the fact that the outer portion of their bodies is much more dense than the inner. It may, in fact, be said, with slight freedom in the use of words, that they are surrounded by a skin, or, to use the term of science, an ecto- sare; the prolongations of their protoplasm for the purpose of locomotion and prehen- sion are permanent, not transient, as in the pseudopodia of the groups just passed, extended or withdrawn at pleasure. In all but the lowest the food is received into the body by one or more mouths; and, with rare exceptions, they are active in their move- ments. Additional points of superiority will be seen further on. Few Infusoria are individually visible without the aid of a microscope; but some- times they form large colonies, which are readily seen. All are aquatic, and wherever standing water appears there are Infusoria. “They abound in the full plenitude of life alike in the running stream, the still and weed-grown pond, or the trackless ocean. Nay, more, . . . every dew-laden blade of grass supports its multitudes, while in the semi-torpid, or sporular state, they permeate as dust the atmosphere we breathe, and beyond question form a more or less considerable increment of the very food we swallow.” Anthony van Leeuwenhoek has the honor of first publishing an account of an infu- sorian. His “Obs... . concerning little animals observed in Rain, Well, Sea, and Snow Water, as also Water wherein Pepper had lain infused,” appeared in the Philos- ophical Transactions, Vol. XII., 1677; the recorded discoveries were made during the two previous years. In Observation I. (1675), four forms are described; of the first he says, “The first sort by me discovered [in rain-water which had been standing four days] I divers times observed to consist of 5, 6, 7, or 8 clear globules... . When these animalcula, or living atoms, did move, they put forth two little horns, continually moving themselves; the place between the horns was flat, though the rest of the body was roundish, sharpening a little towards the end, where they had a tayl near four times the length of the whole body.” There is no difficulty in recognizing by this description a species of Vorticella. It adds fresh terest to these charming animalcules to know that they were the first of their numerous kindred to be discovered. The name “Infusoria” was first used by M. F. Ledermiiller in 1763. Until quite recently it was applied to a heterogeneous assemblage of minute animals and plants having little in common but minuteness. The limits of the group are now pretty well defined ; there are still differences of opinion concerning certain forms, but all students of the Protozoa now agree to relegate the diatoms, desmids, and rotifers to other and very diverse relations. The structure of the individual infusorian as at present limited will now be discussed. The zooids of this group of the Protozoa are essentially unicellular; in the lowest forms they may consist of a naked cell (gymnocyta), or in the higher they may possess a cell membrane (lepocyta). Ehrenberg held that they were complex or multicellular; but this view resulted from his “ polygastric ” theory, put forth in 1830, which has been shown to be not well founded. Among the distinguished investigators who have also advocated the multicellular theory, may be mentioned Diesing, O. Schmidt, L. Agassiz, . INFUSORIA. aT and Claparéde and Lachmann. The unicellular theory was first formally opposed to that of Ehrenberg by Siebold in 1845. It was advocated also by Schleiden and Schwann. Haeckel has pointed out that the life-history of an infusorian, even one of the highest, is only an epitome of the life-history of a simple cell. Kent, in his Manual of Infusoria (1880) holds “that all infusorial structures possess a unicellular morphologic value only.” It seems to the writer that most living students of the Invertebrata hold this view. The bodies of the lowest members of the group (for example, Mastigameba simplex) are composed of simple protoplasm, exhibiting little or no difference in density between the inner and outer portions; in fact, their shape is but slightly more constant than certain Amocbe ; the possession of a flagellum alone pointing out to the observer that the object under the assisted eye is not a rhizopod. On the other hand, those of the higher members of the group, as the Vorticellida, Fig. 44, have clearly more dense external layers, either of naked protoplasm or of the same surrounded by a cuticle of formed matter. Haeckel has described four distinct layers present in the bounding walls of the highest typical forms. The first is an outer, delicate, hyaline, elastic membrane; this in the sedentary, stalked species, extends down as the sheath of the pedicle, while in others it takes part in the forma- tion of the carapax, as in Huplotes. As secondary products also may be mentioned the lorice of Cothurnia and its allies (Fig. 21); again, in Oph- rydium, it surrounds the zooids as a thick mucilaginous sheath, binding thousands of individuals into colonies. The second is a highly contrac- tile layer just beneath the cuticle, called the ciliary layer; from this arise the cilia and their various modifications. The third, found only in the / highest Ciliata, is termed the muscular layer; it is prolonged through the EE stalk of Vorticella, giving that organ its eminently muscular function; ™S;7 00g" it is highly developed in Stentor and in Spirostomum ; in the former the fibrille are arranged longitudinally, in the latter they have a spiral disposition. The fourth of these layers is that in which the trichocysts (rod-like bodies possessed by cer- tain forms) are generated. The contents of the complex bounding wall, or ectosarc, consists of the more fluid protoplasm of the organism. This transparent, colorless sarcode, the endosare, contains numerous minute dark-colored granules, food particles, oil globules, foreign bodies, and an important body which requires special notice, the nucleus. This is usually a more or less oval body, differing somewhat from the surrounding protoplasm in density, etc., and in the fact that it is stained more readily by reagents, thus enabling the observer to easily distinguish it. In many cases, particularly among the simplest Infusoria, Huxley says, that “the ‘nucleus’ is a structure which is often wonderfully similar to the nucleus of a histological cell; but as the identity is not fully made out, it may better be termed endoplast.” While it has not been absolutely settled that this body is a true nucleus, there does not appear to be any valid objection to the view which would homologize the nucleus of the Protozoa and Metozoa. There are various special forms of the nucleus: it is sometimes ribbon-like, or coiled into a short, loose spiral (Fig. 44, 2), or moniliform, that is, composed of nodular or oval bodies separated by constric- tions; this form occurs in Spirostomum ambiguum (Fig. 22). The nucleolus or en- doplastule, when present, is, in the spherical forms, enclosed within the nucleus, while in the sausage-shaped nuclei it is often outside, attached to the lateral wall. It has been demonstrated beyond question that in the more complicated types this 28 LOWER [NVERTEBRATES. VT igri Wis FIG. 22,— Spirostomum ambiguum, greatly enlarged. organ is enclosed ina membrane. The func- tion of the nucleus will be referred to fur- ther on. The contractile vacuole is present in the majority of species. There may be only one (the usual condition), or several, and in rare instances many; in Amphileptus anser there are from ten to fifty, arranged in two longitudinal series. It is an interest- ing fact that the pulsations of these vacuoles occur, first on one side, and then on the other, progressing from the anterior to the posterior end of this elongate form. The vacuole may be simple or quite complex. ‘When simple it is more or less spheroidal; in an active animalcule under the micro- scope it may be seen to steadily fill with a clear, watery fluid; when the full size is reached it suddenly collapses, after which, often, no trace of it appears until it begins again to fill; the pulse is rhythmical when the animal is expanded seeking food. Among the complex types may be men- tioned those spherical forms with two or more radiating sinuses or diverticula. In Paramecium aurelia (Fig. 37), there are usually from five to eight of these blind canals; in Stentor polymorphus (Fig. 42, cv.), a sinus extends from the bulb situ- ated near the anterior border down to the foot, while another branch extends from the bulb about the peristome; in Spiros- tomum ambiguum (Fig. 22) it is somewhat similar to that in Stentor, taking the form of a lateral canal with a very large bulb at the posterior extremity; it is often en- larged also at the opposite end. Con- cerning its use, whether it is a true organ with bounding walls, or whether it connects with the external water, there has been much lively dispute; indeed, students are still divided in their opinions of these ques- tions. Ehrenberg regarded it a spermatic gland, Dujardin attributed to it a respira- tory function, Claparéde and Lachmann a cir- culatory function, Stein excretory. Huxley remarks that its function is entirely unknown, though it is an obvious conjecture that: it INFUSORIA. 99 may be respiratory or excretory. Kent considers it fully established that there is con- stant and free intercommunication with the outer water; that it is a mere pulsating lacuna in the cortical layer of the ectoplasm, and that its leading function is excretory, getting rid of the large quantity of fluid brought into the body by the ciliary or other currents incident to the capture and intussusception of the food. The contractile layer of the ectoplasm, 7. ¢. that just beneath the cuticle, bears permanent prolongations which are the organs of locomotion and prehension; hence they must pierce the cuticular layer to come in contact with the surrounding medium; they are long, slender, and represent three well-marked forms, viz.: flagella, cilia, and tentacula. The flagella are long whip-like protrusions of the body substance, often ex- ceeding several times in length that of the body. They are never numerous— one, two, or four are the most usual, although a larger number is not unknown; their use, be- sides propelling the creature through the water, is to assist in the capture of food particles ; in sedentary species they produce currents in the water, directing them against the body. In cases where more than one obtains, they are ordinarily in pairs, or sepa- rate and situated at a distance from each other}; again, one flagellum, or one set, may serve to anchor the animal, while another distantly situated may serve for food capture. Cilia are short prolongations which resemble eye-lashes, hence the name; it is by their rhythmical and vigorous lashing of the water that the infusorian swims about so freely, or, if it is fixed, by the same means water-currents are made to flow past the mouth, and food is thus secured. The various arrangements of these locomotory hairs will be given under the description of the order Ciliata, named thus on account of their characteristic natatory organs. Besides the vibratile cilia, there are other modifications scarcely to be distinguished from them ; these are sete, or rigid hairs, used for support, or for defence ; thick, straight sete, called stylets, usually situated beneath the body, and uncini or curved hook-like hairs. The tentacula, in appearance and motion, at first recall the pseudopodia of some of the Radiolaria, but more careful examination shows that they are different. Each tentacle is tubular; a structureless external wall termi- nating in a distal expansion, or sucker, encloses a core of granular semi-fluid matter, which is an extension of the endoplasm. These organs, situated promiscuously over the animalcule’s body, on well-defined areas, or on tubercles of the peristome border, may be extended, retracted, or even bent at will. In the simplest of the Infusoria there is no constant aperture, or mouth, for the reception of food, but, as in Amceba, it is passed into the body substance indifferently at any part of the periphery. It is plain that in such cases a cuticle cannot be present ; in others a certain definite portion of the surface receives the food. It is safe to consider such forms more highly developed. Among those regarded as the highest of the group, there is a well-defined oral aperture, often reinforced by ap- pendicular appliances, and from which a passage, the cesophagus, leads into the endoplasm. . The multiplication of the Infusoria has been studied with much care. It will be convenient to speak of the several methods: by binary division, by gemmation, by spores, and by sexual reproduction. Examples of sub-division are frequently seen, even by the casual observer. The process was accurately described in essentials by the earliest observers of these animals. In a majority of instances it takes place across the body; after separation of the nucleus into two parts, a constriction first appears at the middle, which increases in depth until the two parts separate, forming two perfectly-formed, free-swimming indi- 80 LOWER INVERTEBRATES. viduals, and the part without contractile vacuole and mouth soonacquires them. Each resulting infusorian, after a longer or shorter time, again divides. Ehrenberg isolated examples of different species, and after ascertaining how long time was required for division computed the enormous numbers produced by this process alone. In some genera, by no means a limited number, the division occurs in the opposite direction, or longitudinally ; it may not infrequently be seen in Vorticella or Epistylis, so that the large colonies of the latter have thus increased from a single zooid. In certain forms, at least, the oral aperture, present before division, is lost, two new ones being formed. Binary division in a limited number of species, for example Stentor, is oblique. An instance of multiplication by gemmation is afforded by Hemiophrya gemmipara (Fig. 23). The buds appear on the anterior border of the parent animal, the nucleus branches, sending out divertic- ula into the buds. This phenomenon probably takes place in other species which bud externally. si tS Hi slant. postdocs, eae Noctiluca miliaris also increases by this process ; blierongutergentovales, magnified200 the nucleus first disappears, then the protoplasm divides, first into two, then four, and so on. These masses are at length protruded upon the surface, the flagella are developed, and finally they are liberated as free-swimming germs. Sporular multiplication, especially among the Flagellata, has been frequently ob- served. The careful and patient researches by Messrs. Dallinger and Drysdale have done much to acquaint us with the phenomena attending this process. In case of the flagellate monads they found each species to pass through several stages of develop- ment in their life-history, viz. : the flagellate or mature form, the ameeboid, the encysted, and the sporular condition ; the last appearing upon the breaking up of the contents of the cyst. In a flagellate obtained in an infusion of cod-fish it was found that many of these organisms all at once appeared to pour out a delicate sarcode, which exhibited amceboid movements. Two of these amceboid masses would unite, after which the sarcode became spherical, and at length developed the true cystic wall. Upon the rupture of the cyst, there escaped multitudes of microspores, not large enough to be individually defined by a magnifying power of fifteen thousand diameters. They were continuously watched until they developed into the initial forms. Similar phenomena have been recorded as taking place in the development of the higher Infusoria. Sexual, or genetic reproduction, in the sense of the union of two distinct and differ- ent elements, has not been proven to occur. As stated above, individuals entirely indistinguishable unite before sporular sub-division. It is also well known that indi- viduals unite transiently, and then separate to each continue multiplication by binary division. That the repeated sub-divisions so exhaust the stock that it must necessarily be revitalized by the conjugation of separate individuals is generally held. It is also recognized that the nucleus and nucleolus play significant parts in the rejuvenesence due to the zygosis, or conjugations. Concerning the interpretation of the facts there is much difference of opinion. A notice of the several views cannot be introduced here. O. F. Miller, in 1786, first attempted to classify the Infusoria. Eleven of his seven- teen genera are still recognized in the infusorial class. The number of species included was about two hundred. Ehrenberg’s more elaborate system, published in 1835, de- scribed three hundred and fifty species (after deducting the rotifers and plants), and separated them into sixteen families and eighty genera. Von Siebold, in 1845, divided INFUSORIA. 31 the true infusorial forms into two orders, —Astoma, without oral aperture and Stoma- toda, with a distinct oral aperture and esophagus. Claparéde and Lachmann, in 1868, for the first time restricted the group to its present limits, and divided it into four orders, I. Flagellata, I. Cilio-flagellata, ITI. Suctoria, IV. Ciliata. Stein in his magnificent work, “Organismus der Infusionsthiere,” not yet completed, presented in 1867 the classification of the Ciliata now generally adopted. The part of the work treating of the Flagellata appeared in 1878; it includes several genera, by many regarded as undoubted plants— for example, Volvox and Chlamydomonas. The latest proposed arrangement, by W. Saville Kent, in his Manual of the Infusoria (1880-82), divides the Legion Infusoria into the following classes: I. Flagellata, II. Ciliata, III. Tenta- culifera. This author’s limitation and arrangement of this group will be adhered to in the following pages, except that the Infusoria will be regarded as a Class; hence, his classes will become Orders and his Orders sub-orders. OrvER I.—FLAGELLATA. The Infusoria of this order bear one, two, or more flagella, which serve them for locomotion, and assist in obtaining food. They were not unknown to the earliest observers. In 1696, Mr. John Harris described what is undoubtedly Huglena viridis ; but the modern microscope alone can reveal their organization, and it is in the study of these lowly organisms that the most substantial progress has been made by recent in- vestigators in this field of research. Reference may here be made to the discovery of the collared-monads by H. J. Clark in 1868, and the addition of numerous species to [ this list by Stein and Kent, and also to the fact that Stein has found many Flagellata more highly organized than had been previously supposed. He has shown that many of ithe Flagellata possess well developed oral apertures, frequently with the addition of a ‘pharyngeal dilation, and occasionally a buccal armature similar to that of the Ciliata. The flagellum is not the only means of locomotion possessed by some species, like Mastigameeba, for these have true pseudopodia like those of Amceba ; others, again, as Actinomonas, have, besides the flagellum, temporarily developed rays like Actino- phrys ; a thread-like pedicle is also present in Actinomonas. Sus-ORDER I.— TRYPANOSOMATA. The very lowest of the Flagellata now known are two parasitic forms, one of which (Zrypanosoma sanguinis) is illustrated by Fig. 24. The animal is flattened, and has a frill- like, undulating, lateral border which serves for loco- motion. It will be seen that one extremity is somewhat prolonged or attenuate, representing the flagellum ; . : : 24,— Trypanosoma sanguinis, the species occurs in the blood of frogs; its congener Tit “aenitied 600 times, aes inhabits the intestine of domestic poultry. Sus-OrpeEr II. — RHIZ0-FLAGELLATA. There ovcur in pond water, hay-infusions, and the lke, some most interesting forms; they are so because they have characters in common with the Ameba, that is, they 32 LOWER INVERTEBRATES. possess, besides the contractile vesicle and nucleus, the ability to protrude the body ‘substance in the form of pseudopodia, by means of which they progress and take food ; but they have in addition long vibratile flagella which place them in the higher group. Mastigameba simplex (Fig. 25) serves well to illustrate this small group. A similar form has been often taken by the writer from the soft mud and débris at the bottom of quiet water ; its movements are comparatively active, and its very long lash is thrust forward, beating the water with its rapidly vibrating extremity. Perhaps the most remarkable species of the Rhizo-flagellata is Podo- stoma filigerum of Claparéde and Lachmann. It is very changeable in shape, and from the extremities of the pseudopodal protuberences flagella may be produced or withdrawn at will. When these are not apparent, the animal closely resembles lmcba radiosa, — indeed, Fic.25.—Mastigam. Biitschli has recently attempted to show that it is the same species ; fated ti Grier” but, on the other hand, it has been pointed out that the feet of Amaba radiosa, however attenuate, are never thrown into spirals, nor vibrate, as in Podostoma. It should be looked for in infusions of hay. Sus-OrDER III. — RADIO-FLAGELLATA. The Radio-flagellata, which follow very naturally the forms last’ mentioned, are mostly marine. They may be compared to the Radiolaria, which they resemble very closely in their ray-like pseudopodia, but, in addition, they are provided with one or more lashes. Again, some of them are naked, while others are provided with silicious cases or lorice. It should be remembered that these genera with tests are included by — Haeckel in the Radiolaria. Is the possession of flagella a sufficient distinction for thus removing these to the Flagellate Infusoria? Without considering the intermediate char- acter of Actinomonas and Actinolophus pedunculatus, it would seem not; but these forms bridge the chasm as well as that between the Rhizopoda and Rhizo-flagellata is bridged. A characteristic example of the sub-order is Actinomonas mirabilis. Its body is globular, supported on a thread-like stalk several times longer than the diameter of its body; from every part of the periphery radiate sarcode rays in search of food; at the top extends a long flagellum which, by its motion, causes water-currents to pass over the rays. Food particles are taken, indifferently, at any part of the surface. Sus-ORDER IV. — PANTOSTOMATA. We have now to consider true infusorian types where the injestive area is dif- fuse, as in the preceding sub-orders, but which lack the pseudopodal appendages which allied those groups so closely to the Rhizopoda. This extensive sub-order includes eighteen families, divided into three groups; viz. Monomastiga with one flagellum, Dimastiga with two, and Polymastiga with three or more. Every one who has used the microscope with any considerable magnifying power in the examination of infusions, or the water of ponds, has doubtless seen minute globose or elongate plastic bodies moving about by means of a single long thread placed at one end of the body. These forms belong to the genus Monas. As now limited, the family Monapip, includes only the naked free-swimming species with one flagellum. INFUSORIA. 33 The earlier writers were in the habit of describing any flagellate, just discernible with their lenses, as Monas, no matter how many flagella it possessed, hence the number of so-called species of Monas is very large. Many have been put into other genera, while others aré still doubtful. It was one of these, Monas dallingeri, that served for the beautiful series of observations on the life-history of the monads referred to on a pre- vious page. These minute creatures can be studied only by means of high powers. If, after long and careful watching, a form is found, otherwise just like Monas, which does not change its shape, it belongs to Stein’s genus Scytomonas ; if the anterior border is truncate it is Cyathomonas ; fusiform and persistent in shape, Leptomonas ; vermicu- lar and spirally twisted with form persistent, Ophidomonas ; vermicular and change- able in'form, Herpetomonas ; if adherent at will by a trailing flagellum, Ancyromonas. This analysis is given to show with what care these animals must be studied before they can be properly referred to their genera. The remaining three families of the Monomastiga differ in having the flagella lateral, or the animalcule with a tail-like filament, or enclosed in an indurated sheath, the lorica. In the genus Bodo, the ovoid, or elongate, plastic bodies have a tail-like filament; they Fic. 26.— Five zooids of Anthophysa, enlarged 1000 times. Fic. 27. —Large colony of Anthophysa, are mostly parasites in the intestinal canal of animals, especially of reptiles and insects. At times they abound in myriads. The encystment of B. lymnct has been recorded by Ecker. On examining the opaque eggs of the pond-snail, many were found densely packed with minute cysts; these bursting, gave birth to swarms of monadiform germs. The two most remarkable and beautiful genera are loricated. Codonceca costuta, an American salt-water form, was described by H. J. Clark: the bell-shaped lorica or case stands erect on a rather long, rigid stalk; the upper part of the cup is expanded and apparently fluted. Kent has discovered another species with a smooth, ovoid lorica; it inhabits pond-water. The other loricated form, Platytheca micropora, differs from the preceding in lying flat upon its support like Platycola of the peritrichous Ciliata ; it is found on the roots of the duck-weed. The first family of the Dimastiga includes singularly striking species, which, by their treelike supports, or zoodendria, may easily be mistaken for an Ejpistylis ; in fact, more than one of the few species have been figured and described as species of the genus named, but the irregular, oblique animalcules bearing two, equal, anteriorly placed flagella should at once determine the proper place of these forms. The writer once found an Anthophysa abundant in a jar of water in which Chara fragilis had been kept for some time; it was taken for A. vegetans. Colonies attached to their granular, fragile stalks were seen, but the greater number were free-swimming. Figs. VoL. L—3 34 LOWER. INVERTEBRATES. 26-28 illustrate a species which the unequal flagella and oblique anterior border of the zooids appear to place in the genus Anthophysa. It was discovered in Spy Pond, Cambridge, Mass., by A. H. Tuttle, who gave an account of it. He fed the monads indigo, which they took readily. When a particle was taken, the longer flagel- lum, which did not vibrate (the short one was in constant motion), was suddenly turned down, carrying the food with it into the oral region. The number of individuals in a group varied from a few to many, giving the larger colonies a mul- berry appearance. Fig. 26 repre- sents a group of five zooids attached by their bases. Fig. 28 is an ideal section showing the outline of the zooids and their manner of attach- ment to a common pedicle, the upper part of which alone remains, the colony having broken away from its anchorage. Kent has recorded the manner of growth of the pedicle in this genus. A colony were fed with pulverized carmine, which they ingested greedily, but it was soon rejected. This was effected entirely at the posterior extremity or point of union with the stalk, which was soon changed in appearance and dimensions, for the rejected particles of carmine were utilized in increasing it; the amber color and striated aspect gave place to that due to the agglutinated opaque carmine. The growth was so rapid that in one group the pedicle nearly doubled its length in half an hour. Among the most graceful forms of this sub-order the species of Bicosceca must cer- tainly be enumerated. They occur in both salt and fresh-water; the globose, urceolate, or ovate lorice are usually stalked, while the contained zooids also are pedicellate, the usual two anterior flagella are unequal. But for the lashes it would be easy to mistake these creatures for a loricate peritrichous ciliate like Cothurnia. There are also in this assemblage several endoparasitic species, —for example, Psewdospora volvocis, which resides in Volvox globator, where it eats up the cell contents; it is figured with a number of pseudopodia, thus recalling Mastigamceba simplex. Another example is Lophomonas blattarum, which, as its name implies, inhabits the intestinal canal of the cockroach (Blatta); it is a plastic form with a tuft of flagella anteriorly. Another para- site, Hexamitra intestinalis, occurs in the digestive tract of Triton ; it has six flagella, four anteriorly and two posteriorly. It swims free or anchors itself by means of its posterior lashes; when in this position it swims about or gyrates from right to left, — twisting the threads into one, and then, reversing its motion, winds them in the opposite direction. FG. 28. — Ideal section of a colony of Anthophysa. Sus-OrRDER V.—CHOANO-FLAGELLATA. This sub-order includes only three families and seven genera. The characteristics of these remarkable Infusoria were first made known through the researches of H. J. Clark in 1868. It is a matter for pride that this honor should fall to an American. A type of these forms is represented in Codosiga botrytis (Fig. 29), with which the other species may be compared. The animals of the family to which this species INFUSORLIA. 35 belongs are naked; those of Codosiga and Monosiga are attached, while those of Astrosiga and Desmarella are free-swimming. Those of the second family are loricate; Salpingeca and Laganeca are solitary, the one sedentary, the other free, while the animals of the remaining genus, Polywca, are united, forming branched supports. The third family has the animalcules united by a gelatinous matter into colonies; the two genera are Phalansterium, with the collar rudimentary, and Protospongia, collar well developed. The form represented in Fig. 29 will at once be seen to belong to Codosiga, for the zooids are naked, stalked, and united socially. The leading peculiarity upon which the sub-order is founded is the hyaline, wine-glass shaped collar, borne at the upper, or anterior extremity of the body. In the centre of this cup arises the single flagellum, which by its motion about the cup causes currents of water to pass in on one side, down to the bot- ’ tom, and out on the other side; the discal area at the bottom of the collar receives -- the food; waste particles are also rejected at this point. The collar may be with- drawn into the body, and again protruded at will. Codosiga botrytis appears to have been described by Ehrenberg, under the genus Epistylis of the peritrichous Ciliata. According to Kent it is Codo- siga pulcherrima of Clark. They in- crease by binary division, as shown in Fig. 30. (C. botrytis has also been ob- served to withdraw its collar and flagel- lum, and protrude rod-like pseudopodia from its surface, after which a cyst formed over the body contents, the latter ulti- mately breaking up into sporular bodies. The pseudopodal spines sometimes occur before the disappearance of the collar. This cosmopolitan species should be looked for on aquatic plants. Mono- siga steinti is not uncommon on the stems of Epistylis plicatilis. When one of the pedicles containing them is examined with a magnifying power of six hundred diameters or upwards, the minute, solitary, sessile zooids of AZ steinii may be seen to good advan- tage. One other genus of the group can alone be mentioned; it is Salpingeca, of which there are nearly thirty species known. The animals are, if possible, more beautiful than those already mentioned ; for they have, in addition to the graceful outline of the zooid, an equally graceful lorica. S. amphoridium, described by Clark, has a very wide distribution; it abounds on conferve, the sessile lorica often incrusting the plants. They have been seen to divide, the separated portion moving away by means of pseu- podia; in this condition it has the appearance of Ameba radiosa. After a time it == Fig. 29.— Codosiga botrytis, greatly enlarged.’ 36 LOWER INVERTEBRATES. secretes a lorica of the pristine beauty of its species, soon acquires a collar and flagellum, and is henceforth indistinguishable from its mature kindred. In the recently described Spongomonas haeckeli, we are made acquainted with a most remarkable infusorian,—one which, if it fulfils the expectation of the discoverer, Mr. Kent, will prove of unusual interest to a large number of students in zoology, and its dedication to Prof. Haeckel particularly apt. The zooids differ from the preceding only in being more plastic, the collar and flagellum being suddenly withdrawn on the least disturbance, the body then taking on an ameboid aspect. The animals secrete a mucilaginous stratum in which they dwell, studding its surface when expanded. Should this disposition of the zooids take place in “sacular invaginations of this matrix, it would produce what would have to be accepted as an undoubted, though very rudimentary, Fie. 30.— Fission in Codosiga. Sponge-stock.” SuB-ORDER VI.—EUSTOMATA. The Eustomata differ from the forms previously described, inasmuch as they have a definite oral aperture, instead of ingesting their food at any part of their sur- face, or, as in the collared monads, only at a disc bordered by the collar; they differ also in having the outer part of their bodies much firmer than the endosarc, hence they are as a rule less plastic, and in a few instances the outer layer is indurated after the manner of some of the higher Ciliata. They never have more than two flagella, so they are separated into groups of families, according as the zooids have one or two flagella. The forty-six genera are distributed among eleven families; there are in- cluded many forms well-known to observers of pond-life. In the first family (Astasip.®) the monads are free, constant in form, colorless, the generic differences being found in the shape of the body,— ovate, flattened, flask-shaped, ete.; it includes Astasia with a distinct tubular pharynx, and Colpodella without it. Astasia trichophora is frequently met with in marsh-water. Although its forms are protean, perhaps its more usual attitude is pyriform ; from the narrower anterior end issues a cord-like flagellum, mistaken by Ehrenberg for a neck like that of Zrachelocera olor (Fig. 39). The ingestive orifice “consists of a large, widely dilatable, but simple, aperture, continued backwards into a clearly-defined pharyngeal tract.” This structural character marks a broad distinction between this genus and Euglena. Biitschli has shown that the contractile vacuole of A. trichophora by its contraction forces a part of its contents out into lateral canals in a manner similar to that in Paramecium, and others of the Ciliata, to be described further on. The second family comprises forms highly changeable in outline, and colorless. The Everenip differs from the Astaside in having the endoplasm brilliant green, and in having an ingestive apparatus capable of taking only minute particles. Huglena viridis 1s known by, or has been seen by, every tyro with the microscope. Its developmental forms are so various that it has been described under many names. Stein has ob- eae aman served a division of the nucleus to take place; the separate masses in omonas hispida, some instances acquire an ovate outline, surrounding themselves with ified : : 3 umes, a dense coat, while others become thin-walled sacks, full of minute gran- INFUSORIA. 37 ules, each of whick is provided with a single cilium. The loricated form, otherwise agreeing with Huglena, is Trachelomonas, common in ponds and bog-water. Asco- glena differs from the last in being sedentary ; from this Colaciwm differs in the absence of the sheath, and in having a branching pedicle. The phosphorescent Nocritucip.# embraces the genera Voctiluca and Leptodiscus. N. miliaris (Fig. 32) is a large form, visible to the naked eye, found in immense num- bers in the superficial waters of the ocean, and it is one of the causes of their phosphorescence. It is colorless, spherical, with a meridional groove on one side, at one end of which the mouth is situated. A long, slender, transversely striated tentacle over- hangs the mouth, on one side of which a hard, toothed ridge projects; close to one end of this is a vibratile cilium. The protoplasm consists of a central mass, with radiating portions connecting it with the sub-cuticular layer; there is a funnel- shaped depression leading into the vacuoled central mass, through which the food passes into the same. The phosphorescence appears to emanate from the layer just under the cuticle; for it has been observed that as the light gradually fades away on the death of the animal, as when one has been immersed in alchol, that the light finally appears in a ring around the body, since the observer is looking down upon a thin spherical film of light, imperceptible in the single layer over the middle of the globule; but at the borders, where seen as if on edge, sufficient light is sent forth to make it visible. When disturbed they become more highly luminous, so that a fish, for example, moving through the water where they are abundant shows its luminous sides, and its course is marked out by a path of emerald green light. This form is comparatively common in European seas, but has only been found, so far as we are aware, by Mr. C. B. Fuller at Portland, Maine, and by Prof. Hyatt and Mr. Kingsley at Annisquam, Mass. Among the second division of this sub-order — viz. mouth-bearing, two flagellate forms —are many interesting and well-known species. The Entomostraca, especially those in puddles of the forest in spring time, are often loaded down with a green, oval form, which stands singly, or in groups, on short pedicles. On superficial examination it would be easy to mistake it for a Colacium,; but on account of its two flagella during the motile period, its firmer cuticle and its two lateral pigment bands, it has been separated from Colacium as Chlorangium stentoriuum. Whether the flagella remain during the sedentary stage or not has not been determined. In Uvella the animalcules are in colonies, free-swimming, and the flagella are sub-equal. Two loricated genera, Epipyxis and Dinobryon, are unsurpassed in beauty by any of their kindred. The lashes are unequal, and the animal is attached to its vase-shaped lorica by a posterior, contractile fibre; the individuals of Hpipyxis are sessile upon conferve, while those of Dinobryon occur in branching chains of lorica ¢.e. each individual set free by sub-division is attached to the inner margin of the case of the parent. In early summer a species, presumed to be D. sertudaria, abounds in the water- supplies of cities along the Great Lakes. Sus-OrpDER VII. — CILIO-FLAGELLATA. The animalcules of the Cilio-flagellata have one or more lasb-like flagella, and, in addi- tion, a more or less highly-developed ciliary system, thus indicating a position between the Flagellata proper and the true Ciliata. At first only the Peridinide were included, 88 LOWER INVERTEBRATES. but recent investigations have considerably enlarged its borders. It now embraces five families, the typical forms being included in the Permpinipz. These are free-swim- ming animalcules, sometimes naked, but in most cases the body is enclosed in a hard case, variously ornamented, the angles sometimes being prolonged into long spines. The case or cuirass has recently been proved to be cellulose, a substance hitherto only known in the Ascidians, outside of the vegetable kingdom. The cilia occur as a central or eccentric girdle, more or less complete; in the cuirassed forms the shell is usually divided by a groove, the borders of which are ciliated. The shell is either composed of one uniform piece or is made up of plates. There arise from some parts of the body one or more flagella. In life these flagella are seen to suddenly disappear, and a close examination has shown (in Ceratiwm) that there is a small cavity situated at the base of the flagellum into which that organ retreats, bringing with it foreign bodies which serve for food. The nucleus is usually spherical or oval, while a contractile vacuole is occasionally found. They are, like Woctiluca, highly phosphorescent. They have been ob- served to become encysted, when segmentation, on a more or less extensive scale, occurs. In some cases the cyst is en- closed in the carapax; in other instances the cuirass is thrown Fic. 33.—Cilio-flagellate, en- Off, and a new cyst of a different form is secreted, which often cysted, enlarged 300 times. has one or both extremities prolonged into attenuate curved horns, giving it a crescent shape (Fig. 33), resembling certain desmids ( Closteria). They sometimes hibernate in this condition. They occur in both salt and fresh water. Of the ten genera of the Peridinide the species of three are naked, that is, resemble in essentials those of the loricate forms which have thrown off the case previous to encystment. Gymnodinium pulvisculus is, per- haps, as often met with as any; it occurs among Alex in pools, often in great numbers, is somewhat spherical, with a transverse groove, and is brown or yellow in color. The best-known genera are Glenodinium, and Peridinium without horn-like processes, and Ceratium, with conspicuous processes on the shells. G. cinctum is well known to observers ' . x ake .. .. FIG. 34.— Gymnodin- of pond-life; its smooth case should distinguish it ium _—_ lachmannit from a similar Peridiniwm with faceted carapax. Slee, rene These genera are represented by several species in American waters. Mr. H. J. Carter has described a most remarkable instance of the coloring red of the waters around the shores of the Island of Bom- bay by P. sanguinea. During its active stages this species is green and translucent; gradually, as the time approaches for it to assume its quiescent or encysted state, refractive oil globules appear within the interior, and the green gives place to red, and thus the water containing them acquires a deep vermilion hue. It is probable that other instances of red waters are due to similar causes. The characteristic Ceratium (Fig. 35) appears to be a cosmopolitan infusorian. It has been known a long time as C. longicorne, but R. 8. Berg has recently indentified it with Bursaria hirundinella Ss Fe canna, eae of O. F. Miller, which, if correct, will change the specific name to times. the one having priority.- C. hirundinella occurs often in large numbers in the water-supply of all the cities along the Great Lakes. It is most abun- INFUSORIA. dant in the fall. It may be said always to occur in these localities, together with a rotifer, Anurca longispina, which has singularly long anterior and posterior spines corresponding in number with those of the infusorian. The resemblance is striking. Mr. J. Levic has recently found the same forms together in Olton Reservoir, near Birmingham, England. The species of the remaining families have one or more flagella (usu- ally one), with the body more or less clothed with cilia; in some the whole surface bears them, in others only a crown of cilia occurs at the anterior end, the flagellum standing in the midst. Asthmatos ciliaris (Fig. 86) exemplifies this structural peculiarity. This species occurs in the mucus from the nasal passages of persons suffering from “hay fever,” and is held by Dr. J. H. Salisbury to be the cause of this distressing complaint. OrpDER II. — CILIATA. 39 Fic. 36, — Asth- matos ciliaris magnified 506 times. The animalcules of this great order, as the name implies, possess cilia as locomotory organs. They are much more highly organized than the Flagellata, and many of the forms included are generally better known, and are more generally called to mind by the name Infusoria. Stein’s division of the order into suborders is as follows: Holo- tricha, with cilia over the whole surface; Heterotricha, with cilia distributed over the entire surface, having those near or surrounding the mouth longer; Peritricha, cilia mostly in a wreath about the mouth; and Hypotricha, with cilia on the ventral surface only. Sus-OrpDER J. — HouotricHa. A common type of the first sub-order and of the family : ParaMEcipz is Paramecium aurelia (Fig. 87). It occurs “2s 3 in hosts in vegetable infusions, stagnant pond-water, etc. ; These active, elongate, animalcules are alike the delight of the amateur microscopist and the joy of the veteran inves- ages tigator; it is to him what the frog is to the general anato- mist and physiologist. It was made for investigation; the comparatively large size and transparent body fit it admirably for study, and it has not been neglected. The anterior third of the body is somewhat flattened and twisted, so that the flattened face resembles a living figure of 8; near the middle of the ventral face—at the posterior extremity of the 8 — the mouth is situated. The rejectamenta issue at a point about half-way from the oral aperture to the posterior ex- tremity of the body. There are two contractile vacuoles near the extremities. ]When expanded they are round, but when contraction takes place there appear fine radiating streaks, ow a= te gS a ale yn Gans ws6enhee eee 7 Foss Fee which, as the main portion decreases, gradually broaden, "18.3% Aivamecium aurelia, Be, i i invisi tractile vacuoles, d. Mouth. until, when the former is nearly invisible, they are extended — fragtine vac gt Mood saa: over half the length of the body. It has been suggested woles. %. Nucleus. m. Endo- sare. 40 LOWER INVERTEBRATES. that. these phenomena are really due to abnormal pressure of the cover glass. Para- mecia increase by transverse fission. The cortical layer contains numerous vertically disposed rod-like bodies called trichocysts. When a Paramecium is treated with very dilute acetic acid these protrude from all parts of the surface, giving the animal the appearance of being clothed with very long cilia. A solution of tannin in glycerine pro- duces a similar effect, although it is claimed by a writer in the Journal of the Royal Microscopical Society that it is due to a hardening of the cilia. These trichocysts have various forms and dispositions in different species. Some regard them as ho- mologous with t!:c thread-cells of the Coelenterata, and as having a similar function; others regard them as tactile organs. Biitschli has described a‘ species, Polykrikos schwartzié, which has trichocysts entirely similar to the thread-cells of the sea-anemone. Since this infusorian inhabits salt-water, and the trichocysts are irregularly disposed, Kent suggests that they may be thread-cells which have been swallowed. Paramecium bursaria (Fig. 38) is shorter and broader than P. aurelia, and is less flattened; the buccal fossa is funnel-shaped, extending obliquely from left to right. The nucleus is oval and the nucleolus is attached to the side of it. P. bursaria is usually colored green by chlorophyll granules, — now TAT held by some to be parasitic algz, as is also the green color of the fresh- Free) baaié water sponges, and the common green Hydra. Owing to the presence magnified 250 of the green corpuscles the circulation of the endoplasm is seen to better advantage than, perhaps, in any other infusorian, although there are forms like Vorticelle which exhibit this phenomenon in a marked degree. This rotation is uniform, ascending on the left side, and descending on the right, when seen from above (indicated in the figure by the arrows). Balbiani has shown that the so- called longitudinal fission is not really a fission, but a phase of the act of conjugation. Two animalcules may remain attached by their anterior extremities for several days; after separation, the nucleus and nucleolus changes, the latter becoming more or less striated, while the former breaks up into a variable number of spheroidal bodies, which finally separate from the parent, and possibly are to be considered as ovules. Among the most curious of ciliate Infusoria those of the family TRacHELOCERID.© are entitled to the front rank. Their flask-shaped bodies are drawn out anteriorly into a long flexible neck, with the oral aperture at its terminus. Zrache- locera olor (Fig. 39) is the type of the 2 group; it appears to be cosmopolitan, Fra. 89.— Trachelocera olor, enlarged 378 times. v. Contractile occurring among alg in ponds and streams. Under examination in the living state it appears to be incessantly exploring for food, thrusting its wonderfully ex- tensile neck right and left into every cranny. As it swims gracefully through the water, with a spiral motion, its form and attitude very naturally suggest the swan. In Lachry- maria the neck is only slightly extensible. Maryna socialis, as its name implies, affords an instance somewhat rare among the Holotricha, that is, the formation of a zoocytiwm. This structure is branched like a tree, the cup-shaped zooids projecting from the termina- tion of the branches. -Amphileptus gigas is an elongate compressed animal, which may easily be mistaken for a Zrachelocera on account of its long neck, which assumes as many shapes as in that genus; it is readily distinguished, however, since the mouth in Amphileptus is at the base rather than at the apex of the proboscis. It is said to feed INFUSORIA. A1 on animalcules, which it takes by means of its trunk, transferring them to its mouth, after the elephant’s manner of feeding. It has a number of contractile vacuoles, from ten to fifty, arranged in two longitudinal rows. as mentioned on a previous page. It is one of the largest known Infusoria. The next family (Trichonympuip#) is characterized by the possession of a mem- braniform expansion as well as cilia. The type may be illustrated by the interesting Trychonympha agilis (Figs. 40 and 41), described by Leidy as parasitic in the digest- ive canal of the white ant, Termes flavipes. He observed that the canal was dis- tended by brown matter, which on examination proved to consist largely of infusorial, WY SQ SS SS: SSS — = — =— — —— ——= —= — = SS | f hy Figs. 40 and 41.— Trichonympha agilis, enlarged 450 times. n. Nucleus. 4. Ingested food particles. parasites and particles of wood. Three species, belonging to as many genera, were dis- covered. Fig. 40 represents 7. agilis in its extended position. As it progresses in its medium it takes on many protean forms. The cilia are arranged apparently in series, some longer than others. The oral aperture is terminal. Until its life-history shall have been made out, its place in the system and its relation to its companions are uncertain. The mouthless Holotricha (Opatinip2) are all parasitic, degraded forms. They have been taken for the larvee of Distome. These now unquestioned Infusoria should be looked for in the intestines of frogs, mollusks, and worms. Opalina and Anoplo- phrya are examples. Sus-OrpeER II.— HETEROTRICHA. As was mentioned on preceding page, the Heterotricha are characterized by the possession of cilia on the whole surface, those surrounding the mouth being longer than those on other portions of the body. In all except Bursaria and its allies the above definition holds good; there the oral cilia do not encircle the mouth. With the mention of these exceptions, we may now pass to a consideration of a few of the typical forms. In Spirostomum are met Infusoria which at once arrest the attention, both by their elongate, snake-like form and their remarkable anatomy. Spirostomum ambiguum (Fig. 22) may serve to illustrate their striking features. The figure represents the 42 LOWER INVERTEBRATES. animal somewhat contracted. It is capable of great distention, so as to become fifteen or twenty times longer than broad; it then attains a length of one-twelfth of an inch, or even more. Its cylindrical body, sometimes flattened, is rounded at the extremities, often truncate posteriorly. The single line of peristomal hairs extends down the left side of the anterior ventral face to the oral aperture, situated near the middle of the body. The remarkable contractile vesicle and nucleus have been referred to al- ready. The generic name was given on account of the apparently spiral peristome, as seen when the animal twists itself about its long axis. The writer recently found this species so abundant on ascarcely submerged moss that the water taken up by a dipping-bottle was rendered turbid by them. The solution of tannin in glycerine, previously referred to, appears to be a valuable reagent for studying this animalcule. The Stentors, or trumpet animalcules, are among the most entertaining heterotrichous In- fusoria. They are large, active, and often highly colored, so that a colony of them incessantly ex- tending and retracting their bodies, at the same time driving, by means of their oral cilia, strong currents of water against their peristomial sur- faces, presents a scene, when well defined by the microscope, not soon to be forgotten. The ex- cellent cut (Fig. 42) of Stentor polymorphus, a widely-distributed form, displays the characteris- tics of the genus far better than words can do. The Stentors often secrete gelatinous sheaths, which sometimes embrace several individuals. This group has, too, its species which secrete a lorica, and as in other cases they are very attrac- tive objects. An example may be cited in Fol- liculina: its flask-shaped sheath is attached by the side, the neck being bent upwards. The F animal closely resembles a Stentor, except that _&A the peristome is two-lobed, instead of nearly cir- ae ee Jae rinen to tee, cular. The species are defined according to the shape of these lobes. olliculina ampulla has been found in America by Dr. Leidy. In Chetospira the two lobes give place to a slender ribbon-like extension of the anterior region, which, when extended, is twisted into a spire; a hyaline expansion also extends laterally along the broad part of the peristome, giving the extended zooid a unique appearance. It is not attached to its surrounding sheath. The preceding loricate forms are sedentary; on the other hand, Tintinnus includes free-swimming species. The beautiful tests of these are common in the water-supplies of most American cities. In the genus Codonella there are an outer circle of twenty tentacle-like cilia, and an inner one of lappet-like appendages; the case is similar to that of the preceding. INFUSORIA. 43 Sus-ORDER JII.—PERITRICHA. This group resembles the preceding, and indeed there are a few forms whose exact position is doubtful. The typical Peritricha, however, have the cilia confined to a circle around the mouth, while it is only in the aberrant forms that supplementary cilia are found. The members of the sub-order are divided into two not very natural divisions, according as they are free or attached, at least during a portion of the existence of the individual. The attached forms frequently develop elegant cases, or in other instances beautiful branching colonies. As an example of the first (free) group we may consider the unusually active Hul- teri, which are globose forms seen in water from ponds, especially after it has been standing for some days. They have a spiral adoral wreath of cilia for swimming, and usually, in addition, a girdle of long-springing sete, by means of which they leap com- paratively long distances. One may be quite under the observer’s eye, when to his an- noyance instantly it darts out of the field of view. To facilitate their study Claparéde and Lachmann recommended placing under the cover with them a form like Acineta. They soon jump against its sucking tentacles, where they stick fast, and then may be conveniently examined. Fig. 43 illustrates Halteria volvox. It resembles the more common H. grandinella in form and in leaping or- gans, but has besides an equatorial zone of long, re- curved cilia. A singularly aberrant form appears in Torquatella typica, described by E. Ray Lankester. Fre. 3. — Halteria volvox, greatly enlarged. Around the front margin there is a membranous ex- pansible frill, which is plaited, and alternately closes up and expands with a twisting motion. It was obtained in salt-water from decaying eggs of the worm TZerebella. Any one having examined the common Jydra, or the gills of Mecturus lateralis to any extent with the microscope has doubtless encountered minute bodies gliding over the surface of the hosts, or now and then swimming rapidly away, but soon returning. Seen from above they are discs; from the side, shaped like a dice-box. Prof. H. J. Clark studied carefully their anatomy. He showed that the body surface between the concave extremities is ribbed by the thickenings of the body walls; that the posterior truncated margin produces a thin annular membrane called the “velum,” into the base of which, and on its inner side, the posterior fringe is inserted; that the nucleus, ex- amined in the fall, was a moniliform, band-like spiral situated near the truncated base. Besides the vibratile cilia of the border of the posterior disc, there is on its inner border a wreath of stout hairs or uncini, in an outer and an inner series; those of the outer circle are stout and curved, the others, slender, straight, and apparently radiating from the centre of the discal area; they consist of a solid portion and a membrane-like expansion. These forms belong to the genus Zrichodina. The family VorticELLip# includes the attached forms of Peritricha. The three sub-families are Vorticelline (naked), Vaginicoline (loricate), and Ophrydinz (in gela- tinous covering). The student of protozoic life must ever find the keenest delight in the study of this varied family, examples of which may be found at any time of the year, or at any place where there are natural or artificial bodies of water. In Vorticella, the type of the family, each individual is solitary, and consists of an oval body attached by a 44 LOWER INVERTEBRATES. slender stalk to some foreign support. At the end of the body farthest from the sup- port, a band of cilia surrounds a flattened disc, at one side of which is the opening dignified by the name of mouth. On careful examination it is seen that the band of cilia does not form a complete circle, but rather a spiral, the inner end of which passes into the mouth and down the tube known as the esophagus. The nucleus is sausage- shaped, and in many forms is coiled in a spiral. The stalk is also an interesting portion of the anatomy, as \| II) if} _-h Within the external cuticle one may by careful examin- Infusoria, it may be well to give here a slight account of its method of life, as illustrative of the physiology of the whole class. On placing a little powdered carmine in the water in which the Vorticelle are living, and ex- amining them under the microscope, it will be seen that the motion of the cilia around the mouth creates a cur- rent of water, which pursues a constant direction down the esophagus and then out again. The particles of carmine and other small bodies in the water follow the general course of the current down to the bottom of the cesophagus but are not allowed to go out again. In this FIG. 44.—Vorticella nedulifera, enlargea WAY & ball of nutritious matter is formed, which soon about 600 times. a. Cilia. |b. Cili- forces its way into the protoplasm of the body, where it ated disc. c. Peristome. d. Vesti- * bule. ¢, @isophagus. f. Contractile ig known as a food vacuole. These food vacuoles keep vacuole, g. Food vacuoles. h. Nu- i cles. cola Cautosare. k. Ectosare. up a constant though slow motion through the body, passing down on one side and up on the other, until at last all nutritious substance is digested, when the rejectamenta are forced out into the beginning of the cesophagus and carried away from the body by the outgoing current of water. It requires considerable time and much patient watching to make out these points in Vorticella, for though attached, these animals are far from stationary; every few mo- ments the cilia will be suddenly withdrawn, and the animalcule will itself as suddenly dis- appear. On moving the slide one readily ascertains the cause of this, for it will be seen that the contractile protoplasm of the stem has exerted its powers, and the long, slender stalk is now coiled in a close spiral. Gradually the stalk straightens out, when the contractile vacuole renews its pulsations, and the cilia begin their vibration as suddenly as they had stopped them a minute before. The process of binary division in these familiar objects is of high interest; it is longitudinal; first the ciliary disc is withdrawn, and the body assumes a spherical con- tour; it soon becomes dilated, and a notch appears in the anterior border; a new vestibular cleft and oral system is developed on each side of the median line; a line of division now proceeds from the anterior notch, through the centre of the animal’s body, cleaving both the contractile vesicle and nucleus. The result is two animalcules on a single stalk. One zooid remains attached to the original pedicle, the other, with its peristome usually contracted, develops round the posterior region of the body a circle of cilia, by the action of which its attachment to the pedicle is broken, and it swims away, soon to attach itself and acquire a new stalk. Then the temporary girdle of cilia is -7 si ation see a core of contractile protoplasm, whose func- oc\\\ WE _g_ tion will appear further on. SLE a Oe i : cn / BS Since Vorticella is one of the most common of the a SY t INFUSORIA. 45 absorbed, the peristome border is now displayed, and the business of adult life com- menced. Another sort of sub-division has been recorded by Stein, and confirmed by others. The body divides into two unequal parts, after which the lesser one is set free, and then enters into genetic union with some other normal Vorticella. This union is supposed to produce a rejuvenescence, which means a capacity to continue the pro- cess of multiplication by self-division. That the union is followed as in the Flagellata, by encystment and sporular sub-division, has not been demonstrated. Perhaps this word of caution is necessary; the individual Vorticella may often be seen with the posterior cihary wreath. This is not always an indication of recent division, for when these animals become dissatisfied with their surroundings they produce the extra cilia, and remove from the old pedicle, and set up in a more congenial place. Among the forms allied to Vorticella we may notice that in Spirochonia the attach- ment is by means of a disc, and the peristome is developed into a hyaline, spirally con- volute membranous funnel. Stylonichia is similar, except that the body is mounted on a rigid pedicle; in Rhabdostyla the body is like that of Vorticella, but the pedicle is not contractile, but flexible. In Carchesium the zooids are united in social tree- like clusters, but the muscle of the pedicle does not extend through the main trunk; the individuals can withdraw themselves to the point of branching of their stalk, but the colony cannot withdraw itself from its position. In Zoothamnium, on the other hand, the muscle is continuous throughout the colony. In this genus there are zooids of more than one form and size in the same colony. In the genus Epistylis the branched pedicle is rigid throughout, the base of the body alone being contractile. Members of this genus are, doutless, next to those of Vorticella, most frequently met with. Their tree-like colonies are readily seen by a hand lens on aquatic plants. The carapax and gill chambers of the cray-fish, and the shells of aquatic snails, are also rich hunting grounds for these creatures. Opercularia differs from Epistylis in the fact that the ciliary disc is attached to one side of the oral entrance, and is usually elevated to a considerable distance above the margin of the peristome, like a lid. They are often seen as commensals on aquatic larve and Entomostraca. The loricated Vaginicoline is not less rich in surprisingly beautiful forms. Vagind- cola has the sheath erect, sessile, and open at the top. The animalcule is fastened to its case, protruding its body and spreading its peristome; at the least disturbance in its surroundings it instantly retracts, soon to very cautiously again protrude its body. Those species with a lid to close the case when the animal is withdrawn, have been placed in the genus Thuricola. T. crystalina is a common species. If the case is pedicellate and open, the form is a Cothurnia (Fig. 21); if, in addi- tion, theré is a corneous lid, it is a Pywicola; if a fleshy lid, Pachy- trocha. All these forms may be looked for on Entomostraca and aquatic plants, like Lemna, Anacharis, and Myriophyllum. In Platycola and Lagenophrys the cases rest on one side. Fig. 45 represents the charming Platycola dilatata, the brown, laterally at- tached case occurs on fresh-water plants. The animalcule is quite similar to those of a majority of the loricate forms. There are two genera, whose social individuals inhabit common gelatinous matrices, a es viz., Ophionella and Ophrydium. One species of the latter genus, 0. ‘dilatada, magni. fied 300 times, versatile, may often be seen in shallow fresh and salt water as more or . less spherical green masses, sometimes floating or resting on the bottom, and may easily be mistaken for algw, such as Tetraspora or Nostoc. These masses are inhabited by 46 LOWER INVERTEBRATES. myriads of green Iffusoria whose structure does not materially differ from that of LEpistylis, except the greater elongation of the canal-like extension of the contracticle vesicle, which ascends to and surrounds the peristome. A notable structure is found in the thread-like pedicles which unite the individuals of the whole colony. These appear to be homologous with the branched stalk of Epistylis. In Ophrydium sessile the pedicle is wanting, the bodies radiating from one point in the mucilaginous en- velope. O. versatile and OQ. eichornii are known to inhabit American waters. Sus-OrpER IV.— HYPortrRicHA. This sub-order includes numerous families and genera, nearly all of which are free- swimming; their bodies are smooth above, with variously disposed cilia below; they are usually flattened and elon- gate. Chilodon cucullulus af- fords another stock form ; it is as cosmopolitan as Paramecium aurelia, inhabiting both salt and fresh water. It has received many names; its flat, sub-ovate body has the anterior apex turned one side. The cilia on the ven- tral surface are arranged in par- allel lines. Its pharynx is sur- rounded by a series of rod-like teeth. Its food appears to be diatoms, for these plants are often found in its endoplasm. Dysteria armata, described by Huxley, is remarkable for the indurated, complex pharynx. The oral pit is strengthened by a curved rod which terminates in a bifid tooth. This is fol- lowed by the pharyngeal appara- tus proper, which may be said to consist of two parts— an anterior rounded mass in opposition with a much elongated, styliform, pos- terior portion. This partis quite complicated, and cannot be clear- ly defined in a few words. On account of this complicated struc- ture, and the single ventral stylet, it has been considered a rotifer, but recent research has brought to light facts sufficient to warrant the formation of a family with this species as the type. A curious genus is Stichotricha, in which the ani- malcules secrete a domicile; several of the species live singly, but in one the stock is branched, and a social group or colony is the result. This Kent has put in his new genus Fia. 46. — Schizosiphon socialis, ewarged. INFUSORIA. 47 Schizostphon. Stylonichia mytilus, which is abundant in vegetable infusions, illustrates a type of structure somewhat common in this sub-order: the presence of stylets and hooked hairs. It is elongate, elliptical, with a slight left-handed curvature, tapering backwards from the centre; two of the fine anal stylets project beyond the body, the three long caudal setz are radiating ; there are five claw-like ventral stylets and several frontal ones. Huplotes also includes well-known forms. They differ from those of the last-mentioned, first in being encuirassed, second in the styles, although frontal, ventral and anal are represented. Orpver II.— TENTACULIFERA. It remains to introduce some typical forms of the order Tentaculifera. Compared with the orders already described, the specific forms are comparatively few, but their remarkable structure renders them as interesting. Until recently the Tentaculifera were not recognized as a distinct order of Infusoria. By Ehrenberg they were arranged with the diatoms and desmids. Stein in his earlier publications regarded them as developmental stages of the Vorticellide. To Claparéde and Lachmann is due the honor of pointing out their true nature. The term Tentaculifera was proposed by Prof. Huxley, while Suctoria, —the name applied by Claparéde and Lachmann, — has, by Kent, been retained for the division in which the tentacles are wholly or partly suctorial. He has also called those whose tentacles are non-suctorial, but merely adhesive, Actin- aria. The animalcules in their adult life bear neither flagella nor cilia, their embryos, however, are ciliate. Maupas claims that adults of some Podophrye and all the Sphe- rophrye are able to resume their cilia and become free. Their food is taken by means of tentacles developed from their cuticle, the tubular sort terminating in a sucking disc ; and the protoplasm of the body extending into the tentacles. When an infusorian is caught by an Acineta and held at the extremity of one of the tentacles, a rupture is produced in the cuticle of the victim at the point of contact. The axillary substance of the tentacle penetrates this perforation. The tentacle now increases in size, due, doubtless, to a flow of sarcode from the body of the Acineta. On penetrating the body of the prey this sarcode, according to Maupas, mingles with the substance of the vic- tim’s body, and then returns to its place of departure. A nucleus and one or more con- tractile vesicles are usually present. The Tentaculifera increase by division and by budding. SuB-ORDER I. — SucToRIA. The species of Acineta and its allies are numerous; the animalcules have many ten- tacles, while in the genera Rhyncheta and Urnula, there are only one or two; all are stalked, some are loricate, others naked. The Sphwrophrye are free forms, frequently _ parasitic within other Infusoria. Spherophrya sol is found in Paramecium aurelia, S. stentorea in Stentor reeselii, etc. They are spherical, with suctorial tentacles scat- tered over their surface. The earlier stages of the next genus are free, and may be taken for Spherophry, and the latter in turn have been mistaken for the acinetiform embryos of their hosts. The genus Podophrya also includes many species. They dif- fer materially from the preceding in that they are pedicillate, while some species differ from others in having the suctorial tentacles in fascicles. To the latter belongs P. quadripartita, which has been often seen by the writer on the stalks of Zpistylis plica- 48 LOWER INVERTEBRATES. tilis, whose acinetiform embryo it was once regarded. Its stalk is long, the body ovate, with the upper border divided into four tentacle-bearing lobes in the adult; in the young there is but one lobe; this gives place to two, and finally to the full number. According to Claparéde and Lachmann, two sorts of embryos, large and small, are de- veloped ; the former ,enclose a portion only of the nucleus of the parent. According to Biitschli they are liberated through a specially developed orifice; the other forms are produced by the sub-division of the nucleus. In both cases, at. the time of liberation, the embryos are ciliated like the peritrichous In- fusoria, with an equatorial girdle and anterior tuft. In Hemiophrya gemmipara (Fig. 47), we have aremarkable Acinetan. There are two sorts of tentacles, viz., a few, centrally placed, of the usual suctorial type, and a larger number of prehensile ones around the border. When the latter are seen under a high magnification the surface is seen to be : not smooth, but nodular, the component par- REGS eran cage ne ticles of externally developed granular pro- toplasm being usually disposed in a spiral manner around the central axis. The production of embryos by gemmation has been referred to on a previous page. The genus Acineta has many representatives inhabiting both salt and fresh water. An interesting species is found in large numbers on the sur- face of a Mysis taken in the Great Lakes. SusB-ORDER II. — ACTINARIA. This sub-order includes a few forms in which the tentacles are filiform and prehen- sile. They are inhabitants of salt-water, and, like their nearest relatives, are mostly commensal upon aquatic animals. D. 8. Ketticort. SPONGES. 49 Branco II.— PORIFERATA. THE sponges are even now popularly regarded as plants, although for many years naturalists have recognized them as members of the animal kingdom, while the investi- gations of the past fifteen years have shown them to be animals of by no means the lowest type. In the preceding pages we have seen that the unicellular Protozoa do not reproduce by means of eggs, but by a process of division or segmentation, resulting in a varying number of embryos, germs, or spores. All of the higher animals, includ- ing the sponges, are composed of multitudes of cells, each performing its own part in the economy of the individual, and while reproduction by division is frequent in cer- tain groups, all have recourse to specialized cells or eggs for the perpetuation of the species. On account of these differences all multicellular animals have been collec- tively termed Metazoa, in contradistinction to the single-celled Protozoa. There is here a similar relationship to that which exists between the spore-bearing and the seed- bearing plants. In an egg-bearing animal there is a specialization of some of the cells of the tissues and parts to form the male and female reproductive elements, just as in the flowering plant there is a similar specialization of the tissues and leaves to form the male and female products and the organs of reproduction, and as the latter by the union of the sexual elements form fertile seeds, so in the Metazoa the union of the egg, or female element, with the spermatozoan, or male reproductive product, produces a fertile egg. ; In the Poriferata the development of the sexual elements appears in a simple form; parts or cells of the tissues within the body of the same sponge grow larger than the rest, ‘and become eggs while other cells change into spermatozoa. The sponges are, therefore, hermaphrodites, and besides they have no external genital or reproductive apparatus and no special apertures for the extrusion of the young. It has been found, however, that some sponges are female, or at least produce few if any sperm-bearing cells, and these sponges in some cases die soon after giving birth to their broods of young. In most sponges self-fertilization seems to take place; indeed, such would appear to be the inevitable necessity since the male and female elements are enclosed in the same membranes. Sponges are all aquatic, are found in the waters of every part of the globe, and in suitable locations may be exceedingly abundant. So far as known they are all seden- tary animals, constrained with few exceptions to pass all but the earliest stages of their existence fastened to the same submerged object to which they became attached in their early youth. The young possess powers of locomotion and can seek out new places of abode, but the adults must remain in one place and take whatever of food or fortune the passing currents may bring them. Thus they can only live and flourish in places where there are floating clouds of microscopical plants and animals, and their spores. These form their staples of subsistence and must come to them as the rain comes to the plant. They can use for the reception of food only the upper and lateral surfaces of the body, the lower, attached surface, being of course unavailable for such purposes. To this rule there are some exceptions. For instance, Suberites compacta, a sand sponge, has no base of attachment and is apparently capable of living with either side uppermost; there are also some wanderers, sponges which have VoL. 1.—4 50 LOWER INVERTEBRATES. broken away from the base and, still living, are rolled about on the bottom. Some of the commercial sponges are said to be tough enough to stand this. The sponge is typically, or in its most perfect aspect, a vase contracted at the top. In nature it has none of the usual signs of symmetry observed in other animals, and is in most forms even very irregular. There is absolutely no forward or hinder end, except in the embryo; there is no right or left, except again in the embryo. Being a purely sedentary animal, and having no appendages, it has become and usually is des- ignated as amorphous or formless. The conditions which influence growth have caused not only this degradation in symmetry, but they occasion, also, great differ- ences in form in the same species. Thus, while they may be called formless in respect to symmetry, from another point of view they are really animals with more forms than usual. Among those which live near the shores and in the varied conditions of the shal- low water habitats, there is the strangest diversity. Every change of bottom, every change in the surrounding conditions of the current or the place to which the larva may become attached, has some effect upon their aspect. Thus in the same species we find flattened sheets, irregular lumps and clumps, and branching, bush-like modifica- tions of each of these in every variety, and finally vase-like shapes, either imperfect. and open on one side, or perfect and not wholly without grace of outline. If we pass from the varied bottom of the shore-line to one of uniform character, whether the mud bottoms of the deeper waters of the ocean or those nearer shore, or the sandy shallows, where the surroundings and conditions of life are more uniform, we find that the sponges inhabiting these localities are remarkable for greater uniformity of shape within the species. Sponges exhibit most plainly in their forms the direct action of gravity and the peculiarities of the base of attachment. In a sedentary animal the fluids of nutrition would naturally tend to expend their forces primarily, in the early stages of growth at the lowest points of the periphery, and after building the base, cause the sponge to grow upwards in the direction of least resistance. This is practically what happens, and if the rock is smooth and free from other animals, some species, having no heredi- tary form, will grow in a broad sheet without branches; but if the base of attachment be small or crowded, the same sponge will take a bushy, plant-like outline. The force of growth which otherwise would have expended itself in increasing the sponge hori- zontally, is diverted by the strain on the supports or skeleton to the secreting mem- branes of the threads, and we find they become thicker or denser where the strain is greatest, until in some very old sponges the trunks or bases are almost solid. Above, the branches are arranged so that the form is balanced, and there is the same equal distribution of the weight around a central axis as in plants and in sedentary animals of all kinds. This tendency or response of the animal to the attraction of gravitation by equal growth in horizontal planes, so as to balance one side with another, one lateral organ with another, I have previously termed geomalism. Geomalism appears in its primitive aspect among the sponges since they are comparatively soft and sup- ported by a pliable and primitively fragmentary internal skeleton. It will be seen from these remarks that the form of the sponge is more largely the result of the character of the base of attachment than any other cause. When this is uniform, as in a mud or sandy bottom, the form is either vase-shaped or branching and comparatively constant; when upon rocks or irregular surfaces, all forms may occur. Another correlation has been frequently noticed by the writer. In rapid tide-ways a “SPONGES. 51 species, which is flat or chubby in quiet water, will tend to devolop into branching forms. This plasticity of form in response to environment also correlates with the pecu- liarities of the digestive system. The sponges have thousands of minute cavities within the body, devoted to performing the functions of digestion. These cavities re- ceive their food from streams of water, circulating through a double system of tubes, and flowing in through the narrow meshes of a network, formed in the outer covering or skin of the body. With this sieve-like structure there is no use for any particular set of external appendages, and no necessity for any fixed symmetry of form. All that the sponge needs is a capability to adapt itself to its surroundings and the sole requisite of success in obtaining food is the presentation of as much surface as possible, thus securing a large supply of water and accompanying food. Such an organism requires a peculiar skeleton. Since the internal tubes and mi- nute stomachs would be liable to compression by the weight of the soft tissues, after the attainment of a certain size, unless some firmer framework was interposed, we find sd > ‘atl: oN = SFSU AR, WS et Fig. 48. — Portion of a section of a bath-sponge (Spongia), showing the fibrous skeleton, portions of the supply and drainage systems, and the ampulle. in most sponges such a supporting skeleton. In some cases this framework is formed by a woven mass of elastic threads, of a horny nature; in others the framework is composed partly of such threads and partly of stiff and unelastic spicules which may be calcareous or silicious, or in still other cases of a network of spicules united by only a small amount of horny or silicious material. The same principle of construction runs throughout the whole of the Poriferata; the skeletons are really networks or scaffolds of spicules, or of threads permeating all parts of the body, in order to support the whole mass and keep open not only the digestive ampulla, but also the numerous tubes for supply and drainage. A skeleton is not, however, an absolute essential in all the members of any branch of the animal kingdom; thus there are sponges entirely destitute of spicules or threads, but these are mostly flattened or small vase-like forms, in which the weight is small in proportion to the strength of the tissues. In the commercial sponges the skeleton is an intricate mass of interwoven elastic horny threads, as may be seen by slicing one through the middle (Fig. 48). This network 52 LOWER INVERTEBRATES. is permeated by numberless tubes, but these can be reduced into two systems, one lead- ing from the interior outward, and the other leading from the external surface toward the interior. The first or internal system is composed of several large trunk tubes, largest interiorly, but branching and becoming smaller as we approach the exterior. The outer surface of the sponge is ornamented with projecting bunches or ridges of threads. Between these projections there are numerous depressions, the bottoms of which are perforated by openings of medium size, which we can follow as tubes lead- ing into the interior by examination of the cut surface of the section. These are the tubes of the external system. They often terminate abruptly, but here and there are divided into branches, and we can see that they really diminish in size towards the in- terior. Not infrequently these tubes may be traced directly into the trunks of the internal system, but in this case, their walls are thickly set with the openings of small tubules which lead into systems of tubes diminishing in size internally, and therefore belonging to the external system. The dried skeleton looks as if there was no room for fleshy material between the meshes, but the increase in size upon wetting a sponge shows that when in the natural element and fully expanded there is plenty of room between the threads for all the organs we have to describe. The surface of the living commercial sponge is of a dark color, and some species, were they smoother, would remind one of a piece of beef liver. On the upper surface we can see large crater-like openings as in the skeleton, but the surface is otherwise quite different. The tufts of fibres and the depressions between them, which are so marked in the skeleton, are more or less covered with a skin which conceals all the cavities and channels. The tufts, however, do show themselves as slight prominences, while the skin over the intervening depressions is smooth and perforated by groups of holes. These small holes may be opened or closed at the will of the animal, and when open they serve to admit water freely to the external or supply system of tubes. These openings may in many sponges entirely disappear, and new apertures be formed when needed. This faculty has, however, been greatly exaggerated. The superficial cavities are lined with a smooth skin, lighter in color than that of the exterior, while the sides and bottom are perforated by small holes, the openings of the tubules which line the skeletal tubes of the external system and form the fleshy canals of the supply system. These tubes are lined with a light colored skin and branch as they descend into the interior. The tips of the minute branches expand into globular sacs. These little enlargements, the ampulle, open in turn, into small fleshy tubules which line the internal system of tubes of the skeleton. They constitute what may be called a drainage system, and instead of growing less, they increase in size as they go inward, and by uniting with other similar tubes, they form larger and larger branches until they finally open into one of the central trunks. These sieve-like openings, the superficial hollows, and the supply system act as feeders, bringing water loaded with nutriment to the ampulle or digestive sacs. After digestion the refuse is passed out of the ampull into the internal system and thence into the large central trunks which finally open on the outside of the sponge in large crater-like orifices. In some sponges these two systems of canals are not distinguish- able and there is but one outlet to the ampulle. The outermost covering of the body is an extremely delicate membrane composed of asingle layer of flat cells, giving a peculiar shade of purple bloom to the living sponge, but being easily abraded by rough handling. This layer is the ectoderm, and is continuous at the edges of the craters with a somewhat similar layer, lining all of SPONGES. _ Bs the passages of the drainage system, which should be considered as the endoderm. To: this latter system the ampulle belong, but the endoderm which lines them is of a differ- ent character. The tubes of the supply system are doubtless of ectodermic origin. The endodermal cells are usually flat and have polygonal outlines, except in the ampulle, where they give place to oval or even columnar cells, the free ends being crowned by transparent collars, from the centre of which protrudes a long flagel- lum (Fig. 52), These collared cells have unusually large nuclei. The ectodermal cells vary some- what in outline, according to- position, but are usually hex- agonal or quadrangular and rather constant in form. The cells of the endoderm, on the contrary, are subject to extra- ordinary changes, bulging out into balls on their free side when gorged with food, or ex- tending to hair-like cells of en- ormous length when stretched across an opening. Between these two layers lies the middle or fleshy layer of the body, the mesoderm. This is composed of cells, but the intercellular spaces are so abundantly filled with proto- plasm that Haeckel and others consider it as a characteristic of the sponges. We are, however, of the opinion that the abun- dance of intra-cellular substance has been greatly exaggerated, and that the mesodermal cells are numerous and closely ag- gregated. Such we have found to be the case with the Calci- spongie and Chalina, and Lie- berkuhn and Huxley claim the same for Spongilla. The cells Fic. 49.— Section of Halisarca, showing supply (af) and drainage (ef) systems, the ampulla (amp), and eggs in various stages of devel- opment (a, b, c, d, e, of the mesoderm vary considerably in character and appearance. They may be transparent, granular or deeply colored, globular or elongated, entire or amceboid in outline, and capable of extensive changes by expansion or contraction. In many 54 LOWER INVERTEBRATES. sponges there occurs between the undoubted mesoderm and the ectoderm distinct layers, the origin of which is uncertain. One of the most interesting points to the naturalist lies in the history of the skeleton and ‘ its elements. This consists of two parts, the thread of binding substance of horn or keratode and the hard mineralized spicule. All authors apparently agree in considering the spicules as mesodermic, but the origin of the threads has not been so thoroughly worked out. Barrois, however, considers them of ectodermal origin in the silicious sponges, and the author has ex- pressed the same opinion regarding the fibres of the horny sponges. In the Chalinine the same would also appear to be true. The skeletal threads of Chalinula are surrounded by a special membrane, which I have seen in seyv- eral instances, and which may be called the perifibral membrane. This is composed of flat epithelial cells, either transparent or deeply col- ored by granules. They somewhat resemble the cells of the ectoderm in outline, but are longer, fusiform in outline, very closely set, and usually spirally arranged around the fibre. These are evidently the cells which secrete the threads, and in one section I followed this sheath and found it continuous with the ectoderm. We can thus readily account for the skeleton of Chalinula by the presence of invaginated pro- longations of the epiderm which would natural- ly follow and surround first the vertical threads and then others arising'in all directions. The differences in the structure of the inner and the outer portions of the fibres of the Aplysina, and their often hollow condition, can only be ac- counted for by this explanation as well as the fact that in Spongia and its allies the centre of the threads is frequently occupied by foreign matter, carried in from the exterior by the in- vagination of the ectoderm to form the sheaths and subsequently enveloped by the horny mat- ter secreted. The form of the spicules varies greatly, and affords good systematic characters. A few of the forms are shown in the adjacent figure. Some are pointed at one end, some have both extremities acute, while others may terminate at one or both ends like anchors. They may be smooth or variously knobbed and ornamented. i Ay BAX. GUS? Fic. 50. — Different forms of sponge spicules. SPONGES. 55 We cannot hope to disentangle the intricate relations of the parts in such confused structures as the sponges without studying the history of their development. The young can always be relied upon to present the observer with simpler or more element- ary conditions, and generally help us materially in understanding and translating the adult structures. As we have said, the male and female elements are found within the sponge. After fertilization, the egg undergoes a regular segmentation, and then the two ends of the body become distinguishable, one being composed of smaller cells than the other. The embryo is hollow at this the so-called morula stage, but soon the central hollow, the segmentation cavity of embryologists, becomes filled in the following manner. The cells of one end of the embryo become pushed in, much as one inverts the finger of a glove, and these constitute the inner layer or endoderm of the young sponge. In this, which is called the gastrula stage, there are then two layers. In the cal- careous sponges they form a cup with a mouth at one end, but in the carneosponges the gastrula is usually but not invariably solid, the invaginated endoderm completely filling the interior. The mesoderm is developed between these two layers, but from which one is not yet known. The spicules begin to be formed in the mesoderm soon after its appearance, and seem to be due to direct transformation of single cells. These young larvee swim rapidly through the water by means of the cilia, or small hairs, which clothe the exterior, and which can be moved like so many oars ‘with force and rapidity at the will of the tiny animal. The smaller end in the larva of the calcareous sponge is foremost as the little creature moves aimlessly about. When it encounters any obstacle it usually exhibits no ability to back off, but manages by keeping its cilia in constant motion to get away by rolling around the obstruction. At last the embryo settles down, with its mouth or blastopore below, upon the space to which it — P¥6- 51. — Free swistining young of is to become attached. The membranes at this end form a sort of sucker, which spreads itself out and enables the animal to exclude the water between it and the surface to which it is being applied. The pressure of the water holds the sponge in its place, and on some smooth spots this may con- tinue to be its only anchorage, but in rougher situa- tions it naturally acquires additional hold by growing into any cavities or around any projections. On soft, muddy ground fresh-water sponges usually begin to grow upon some small substance, which often fa a Selene puuee aes is very small, and then the weight of the growing sponge of fyosnara ; a, primitive stomach; may sink a portion of the stalk into the mud below. derm; s, segmentation cavity. This portion then dies, but even when dead it plays its part and forms an anchor for the whole structure. We cannot imagine an ordinary sponge growing upon a muddy surface unless the water was absolutely still or the mud hard; otherwise the tiny creature would be suffocated by the sediment. The deep-water mud sponges of the sea (Zyalonema, etc.) have, how- ever, grown so long on soft bottoms that they have developed a system of threads Bé LOWER INVERTEBRATES. which, protruding below, penetrate deeply into the mud, and may either serve as anchors or bases of support. The most curious case of this kind occurs in Tethya gravata, a globular form, in which the threads form a network below, enclosing small stones and gravel. Thus the animal carries ballast, and if turned bottom up in the water it rights itself immediately. When rolled over by the waves upon the muddy bottoms of Buzzard’s Bay, where it occurs, it is always sure to end its gyrations right side up like a bit of leaded pith. The observations of Schultze on the young of Sycandra, one of the calcisponges, show that the ciliated cells, when invaginated, form an ampullaceous sac, confirming the view that we have always held that the typical sponge was a single, isolated ampulla, surrounded by the two layers of the body. A single pore is opened into this sac, and this completes the likeness to one of the Ascones group. The observations of Barrois, Carter, Schultze, and Marshall all seem to show that the ampulle in the silicious sponges have a different development. After the larva has settled, a hollow space appears in the body of the sponge, lined by a non-ciliated endoderm. The ampullaceous sacs arise as buds from this endoderm, communication with the exterior is formed hy tubes, which arise as invaginations of the ectoderm, and grow inward, uniting with the ampulle. The evidence at present seems to be in favor of Barrois’ opinion, that the water flows in through these lateral pores and accumulates in the interior, assisting to raise the soft tissue into a dome or spire, until, at last, unable to withstand the pressure, the top gives way, and the crater is formed. This accounts for the rise of the spire before the formation of the crater, and gives a reason for its disappearance after the pressure has been relieved by the formation of an adequate outlet. Certain it is that the crater is not in any sense the mouth or blastopore of the sponge, as is usually sup- posed. Thus the cloacal apertures have no special morphological location, and arise as purely mechanical necessities, as do the excurrent openings of all colonial forms. The simplest sponges have only a single body cavity, surrounded by ectoderm and mesoderm, and lined by the inner layers. This typical form or vase shape occurs in the young of the calcareous sponges and in the adults of the scones. Individuation in these forms is complete and simple; they are each equivalent to a single ampullaceous sac, separated from any other sponge and surrounded by mesoderm and ectoderm. It is evident, therefore, that when a number of these sacs still remain connected with the body cavity, cach additional sac must be regarded as a bud or offshoot from the ceelomatic cavity, and the whole can be regarded as a branching gastro-vascular system, through which water and food are circulated and excrement discharged. The active collared cells of the ampulle are both structurally and functionally, as was pointed out by H. James Clark, similar to the zoéns of the flagcllated Protozoa; they have the same organization, catch their food by means of the same slender lash, swallow it at the same place within the collar, and throw out the refuse matter in precisely the same manner. The Flagellata are individuals, each having the typical structure of the Protozoa, and though in every respect simple cells, with collars and flagella, as in the separate cells of the sponge, they are not shut up in sacs inside of a mass of flesh, but are free or attached animals, getting their food in the open water. This correlation and the aspect and functions of the cells which form the tissues of all structures in the bodies of sponges and higher animals show us that all ccllular tissues must be regarded as aggregates or colonies, while the single cells of oS which the tissues are composed are the exact morphological representatives of the SaqynowyUad “Tt aus “m94 ‘paovund xhypoojhgovg °% ‘oovyims rapun ‘savavo, nwauowhy *g ‘SHONOdS SPONGES. 57 Protozoa. The sponges are simply less altered than other animals, the cells of the inner layer still retain some traces of their original structure, and we have to rate the Poriferata as intermediate in these characteristics between the Protozoa and the Metazoa. The word ‘individual’ leads to many serious misconceptions owing to its popular meaning, and we use the word zoén for any whole animal or part of a colony of ani- mals whose structure can be said to embrace the essential characteristics of the grand division or branch to which it belongs. In this sense the single cell is a zoén, with regard to the whole animal kingdom, or when we wish to contrast the Protozoa with the Metazoa. The young sponge, at the period when it has but a simple ccelomatic cavity and one opening, is also a zoén, but it is only a zoén when we wish to consider the Poriferata by theinselves. We can test this position by comparison with the simplest known forms of sponges, such as the Ascones. The forms of this group have a vase shape, with only one open- ing above, while the pores for admission of water are formed as wanted. The struc- ture and form of this adult sponge is similar to that of the simplest ampullaceous sac, and is also similar to that of the young when the celomatic cavity is first formed, and it shows us that all these three forms contain the essential elements of sponge struc- ture, and can thus be appropriately called spongo-zodns. After the three layers are fully formed, the coelomatic cavity extends itself in every direction by the formation of ampulle as outgrowths from its sides, but these out- growths do not carry with them the mesoderm and ectoderm. On the contrary, the outward growth and the formation of a new ampullaceous sac, which is the nearest approach the sponge makes towards the formation of a new zo6n, takes place wholly inside of the mesoderm, and the outer layer remains unmodified. This is the case in all the sponges with a thick mesoderm, and even among the higher forms of calci- sponges. " Among the primitive Ascones, however, a bud from the side carries with it all the membranes of the body, and is a repetition of the original zoén, a complete bud or ‘person.’ New craters are formed anywhere as the sponge increases in size, by the conjunc- tion of canals of the drainage system and without the slightest signs of budding, and yet Haeckel and others regard each of these craters as a person or individual. The mass may grow out solidly into a branch with a dozen craters, then, according to these authors, it is one dozen small ‘ persons,’ cr as it grows out, the clozen small canals may unite and form one canal and one crater, then it is one ‘person.’ There are plenty of examples in which such variations occur on the same stock, and we think they prove that the accepted ideas of what constitutes an individual or person among the sponges with a thick mesoderm and branching gastrovascular canals are entirely erroneous and founded on the deceptive resemblances of the branches of a sponge to those of other compound forms, which really arise from true buds and are true zoéns. Haeckel and others have regarded all the vase-shaped sponges as single individuals or zoéns, but this seems untenable, except in the group of Ascones. It is not uncom- mon to trace the form of the same species among living sponges from a flattened disc with several craters to a vase shape, the vase being built up by the more rapid growth of the periphery. The inner portion of the ectoderm on top of the animal thus be- comes internal, and the opening above, the crater of one large ‘person.’ Here the so-called zoén is formed by a transformation which can be clearly proved to be the result of the growth of the external parts. It is evident that the mere fact of the 58 LOWER INVERTEBRATES. existence of a cloacal outlet does not necessarily indicate the presence of an individual. We must regard the whole mass which springs from one base as being an individual, while the buds or branches which may arise from it are not branches, but may be regarded as the prototypes of true buds and branches of colonial animals in other divisions of the animal kingdom. They resemble the branches of other colonies in aspect, and arise from unequal growth of parts in a more or less symmetrical way, and may have any outline essential to the equilibrium of the form, but are no more indi- viduals than are the arms and legs of a human being. The whole mass is the individual, and the fact that it has a branching gastrovas- cular system is accounted for by the budding of the ccelomatic cavity just as the gas- trovascular system of the Hydrozoa and the water system in echinoderms is formed by the prolongation or budding of the walls of the gastric cavity of the larval forms. In fact the similarity of these parts in the Celenterata and Echinodermata indicate to us that the sponges present a much more primitive condition of the gastrovascular sys- tem than do any of the higher types. In the echinoderms, the system becomes sepa- rated into the gastric cavity and the system of water tubes in the early stages; in the Hydrozoa and Ctenophora, the two remain in connection and a true water system is not developed. In the sponges there are two systems, the supply or water system and the cloacal or gastric system, and these two together make a complete gastrovascular sys- tem which, however, is more primitive than either of the other types, combining both the gastric and the water systems in a double set of inter-communicating canals. It is difficult to explain the similarities of the water systems among these animals on any other grounds, and this view enables us to throw some light upon the similarities of the celomatic cavity. This cavity is merely the primitive hollow of the body of the embryo, and in many of the lower forms, as the Hydrozoa, it is the digestive cavity, the cells being modified for assimilative purposes. This is only the next stage above the cellular mode of digestion in which each cell performs this function as in the ampulle of the sponge, and it is an adaptive change both in the structure of the cells and their function. If our view of the affinities of the sponges is correct, this cavity in the Ascones is directly derived from the communal inlet and outlet of some colonial form of Protozoa, and the water system must have arisen subsequently in response to the budding of the celomatic cavity, and the need of special sources of supply for each bud with its ampulle. The correlations in the structure of the feeding cells of sponges and the aspect and similar functions of the cells which form the tissues of higher animals show that not only the sponges, but all the Metazoa, however highly individualized, must be regarded as aggregates or colonies in which each cell represents a zodn of the Protozoa, and which has derived its structure by inheritance from an ancestral protozoon. That is to say, there is such a phenomenon as the inheritance by the single cells of a meta- zoon of the peculiarities and even the tendencies of the independent individualized protozoon, and from this results the communal characteristics of the metazoon which appears to be, but in reality is not, a simple individual. The only simple individual in the animal kingdom is the single unicellular protozoon, or a single cell from the tissues of the Metazoa. This view, though for a time overwhelmed with ridicule, has of late years obtained a quite general acceptance. It dates back to an inspiration of Oken in 1805. The transitions by which it could have taken place have never been satisfactorily stated nor can we here do anything more than add another step towards a final solution. It is now SPONGES. 59 well known that there is no ascertained limit to the action of heredity, and that not only observable characteristics, but even habits and tendencies may be directly trans- mitted from one generation to another. There is a universal and necessary law of heredity which can be used in bridging the gap between the Protozoa and the Metazoa which may be briefly formulated as follows: All animals exhibit a tendency to inherit the characteristics of their ancestors at earlier stages than those in which these charac- teristics first appeared. Thus, if an ancestor or radical form acquired a new character or took on a new habit when adult, this would tend to reappear in the descendants at earlier and earlier stages, and in course of time would become carried back to the adolescent, then to the larval stages, and finally either become useless and disappear altogether, or if useful, and therefore retained, become restricted to embryonic stages. This law was first advanced in 1866, by three persons, Haeckel, Cope, and the writer, almost simultaneously. The Ascones are certainly, so far as known, the simplest or most generalized of the Metazoa, and approximate to the Protozoa in such a way that it is possible with the aid of the law of concentration of development to explain the transformations by which such an organism could have risen from the Protozoa. The egg of all Metazoa is in its first stages a simple cell, and like all other cells is a homologue of an individual or zoon among the Protozoa. This primitive egg cell has but one mode of growth by which it forms tissues. It divides or segments and builds up the primitive tissues of the embryo by a similar process to that by which colonies are formed among the Pro- tozoa. Therefore the egg after segmentation is no longer a single zoén, equivalent to a single zobn among the Protozoa, but a mass of such zodns, differing from the mass of a free colony of amcboid Protozoa in about the same way that the included cells of an ampulla differ from a colony of Flagellata. Among colonial Metazoa we frequently find on the same adult stock, individuals devoted to the performance of distinct functions, and having their shape and structure so modified thereby as to differ widely from each other, though in their younger stages they were more nearly alike. Thus, on the same hydrozoan stock we may find females loaded with eggs, males carrying only sperm cells, sexless polyps devoted wholly to alimentary purposes, others with only defensive functions. We have therefore excellent reasons for assuming that similar transformations took place in the transition from the simple colonies of the Flagellata to the more complex condition of the sponges, and we can make a picture of these changes in strict accord with the laws of morphology. Throughout the Metazoa as well as in sponges, the external layer or ectoderm is protective and builds the protective armor, scales, etc.; the mesoderm is essentially devoted to the formation of flesh and organs of support, while the endoderm is devoted to the function of digestion, and the elaboration of all the parts concerned in this pro- cess; but everywhere these three layers are derived from one cell (the egg). If now we imagine a series of changes, beginning with any flagellate protozoén, and follow- ing out the indications of embryology, we should first have a sheet of attached flag- ellate feeding forms; secondly, these surmonnting or arched above a base composed solely of supporting individuals without collars or flagella; thirdly, the outermost losing their flagella and collars, would become simply protective pavement cells, while the central ones retain their digestive functions; the change slowly becoming more complete, and the central ones acquiring a capability of being withdrawn into the interior when alarmed. The last step would be the inheritance of the invaginated 60 _LOWER INVERTEBRATES. condition, and this would give the vase-shaped Ascones. The inheritance of the in- vaginated stage or of the primitive differentiation of the colony into protective and feeding zoéns in any encysted egg form would be necessarily attended by the forma- tion of a globular shape in which one end would have cells of a different kind from the other, one being composed of endodermal cells inheriting the digestive functions of the original colony, while the other would be formed of ectodermal cells arising from the protective zoéns. This encysted form would be composed of but one layer of cells, and therefore have a hollow interior, and the supporting zoéns or meso- derm would be formed between the other two membranes when it became necessary by the protozoon method of reproduction by fission. We can also reverse this explanation and imagine a sponge, one of the Ascones, being reduced to a protozoén; losing first the form, then the supporting layer, then the protective cells, and finally becoming converted into a layer of zoéns, each of which would closely resemble those to be seen in Fig. 20. The validity of this fe g 3) comparison may be seen by comparing this figure of Codosiga with Fig. 53.—Flagellated the flagellated ampullaceous cells of a true sponge shown in Fig. Cf Svea enPea® 52; and the comparison will also gain when we recollect that in of Sycandra. 5 park 2 the young of the flagellated protozoén the stalk is absent. The normal action of the law of concentration and acceleration of development would alone have caused such changes in the modes of growth of the Metazoa if the latter were really the descendants of the Protozoa, and this series of transformations is included when we say that the Metazoa, in accordance with this law, have inherited the tendency to form colonies or tissues by fissiparity, at an early stage in the exis- tence of the cell or zoén. Thus, the individualized protozoanal stage has become con- fined to the earliest periods of existence instead of being more or less permanent and characteristic of the later stages of growth as in the Protozoa. When the colony be- comes embryonic the process of multiplying by division is, as a necessary consequence, also accelerated and concentrated, and tissues are rapidly formed for different pur- poses. We can therefore, without calling to our aid any but the well-known effects of habit and the law of concentration of development, account for the segmentation of the egg, and the subsequent tendency of the primitive tissue to give rise to the three layers of the Metazoa. The fact that certain cells become differentiated into ees, and others from the same or other layers, into spermatozoa, is not more remarkable than that certain zoéns of many colonial Metazoa, like the hydroids, are exclusively ego- bearers, while others are solely sperm-bearers. The fact that the male element seeks out the egg and becomes merged in it, is paralleled by the process of conjugation among the Protozoa. The sperm cells of the Metazoa, like the germs of the Protozoa, arise by division of a single cell, and, although frequently of similar shape to and swimming freely like many protozoon germs, they do not wait until maturity before conjugating with the females. This is plainly only the inheritance of the tendency to conjugate at an earlier stage, and is a natural result of the law already laid down. It is well known that there is a tendency to reproduce after conjugation, and that conjugation is performed by Protozoa of different sexes, and also that there are sexual colonies among the higher Protozoa. The result of differentiation or progress is evidently towards the formation of sexual differences in the Protozoa as in other branches of the animal kingdom, and if our view is correct, we ought to expect that SPONGES. 61 the Metazoa, springing from the Protozoa, would show similar tendencies toward dif- ferentiation of the colonies. If, as in the sponges, the lower forms had male and female cells in the same body, then the progress of differentiation should lead to a more decided separation of these functions so that some would produce only female and others orly male cells. In other words, the complete separation of the sexes would take place by a perfectly natural transition, and we should have male metazoéns and female metazoéns. The sponges are frequently regarded as degraded Metozoa, but to the author this view seems highly improbable. Huxley first recognized the systematic importance of the sponges, but contrasted them as a division with the rest of the Metazoa, while MacAllister, and subsequently the author, gave them their true taxonomic rank as an independent branch of the animal kingdom. Cuass I.— CALCISPONGLA. This division is somewhat inappropriately named for the reason that some of the genera have no skeletons, but this objection might, with equal justice, be made with regard to the names applied to the other groups. The animals of this class have fusi- form or cylindrical bodies which may be single with one cloacal aperture, or branching with an aperture at the end of each branch, or more or less solid as in the other sponges. When a skeleton is present, the spicules which compose it consist of carbo- nate of lime, and their longer axes are arranged in lines parallel with the canals, that is at right angles to the inner and outer walls of the sponge. OrvDER I. — PHYSEMARIA. This order contains the remarkable genera, Haliphysema and Gastrophysema, which, according to Haeckel, are nearer in form and structure to his archetypal animal form, the gastrula, than are any other adult animals. They are small and vase-shaped in Haliphysema, while Gastrophysema may have from two to five chambers. There is but one aperture above, and the water is drawn into this by ciliary action. According to Haeckel, the body wall consists of but two layers, the ectoderm and the endoderm, but it is evident that the ectoderm of the German savant can be nothing else than mesoderm, for it is composed of loose cells and intercellular protoplasm, while the true ectoderm of all sponges is a simple pavement epithelium and never a compound tissue. In Haeckel’s figure, the whole interior of Halisphysema is paved with ciliated cells, among which are interspersed ameboid cells. Both Haeckel and Bowerbank deny the existence of pores, and it is not likely that even transitory openings would have escaped their observation. ‘The strangest part of the history of the Physemaria is that both Carter and Saville- Kent claim that Haliphysema is a true protozoén, and Kent’s figure, which is as specific as Haeckel’s, depicts a true foraminifer. These observations render it very un- certain whether the group should be referred to the sponges or to the Protozoa. Gastrophysema may be a true sponge, and we therefore describe the order in this connection. Mr. J. A. Ryder describes as an American representative of the group, a curious club-shaped animal with a tough cortex and a cellular interior, under the name Camaraphysema. 62 LOWER INVERTEBRATES. Orprer II.— OLYNTHOIDEA. These forms differ from those of the last order, in having a skeleton of calcareous spicules. These may be either straight and needle-like, or one end may bear three or four rays. The spicules, which are of mesodermal origin, are arranged at right angles to the inner and outer walls of the body in the tube or vase-shaped forms, and the rays being interlaced, afford a firm scaffolding for the support of the walls. Here, as among the Physemaria, Haeckel claims that an outer epithelial membrane is absent, but Grane, Schultze, Metschni- koff, and others have repeatedly demonstrated the existence of a true ectoderm, and the writer has seen this membrane several times in the living sponges. The species are usually colorless, generally of small size, and although abundant along our coasts must be looked for carefully under stones and upon sea-weeds. They are found exclusively in shallow water, and, with few exceptions, do Fig. 54. — Ascaltis, one of the Ascones group. not occur on muddy bottoms. StB-ORDER I. — ASCONES. These forms have a vase-like shape, are thin-walled, and have a distinct skeleton formed of a single layer of triradiate spicules, their bases outward, while the pores of the supply system are formed as they are needed, through the sides. The inner or ccelomatic cavity is lined with flagellated and collared cells, while these, of course, are not found in the transient supply-canals, which, according to Haeckel, are but temporary openings in the sides of the sponge. Sus-ORDER II. — SYCONES. The typical form for the members of this group is that shown in the figure of Scycandra ciliata. The in- : dividuals are attached by the base or Fi6. 55.—Diagrammatic section of small end, and are very like those of the Ascones, but are stouter and more frequently spindle-shaped, while the walls are thicker and more opaque. They are, however, quite dis- tinct in their structure. The flagellated and collared cells are con- fined to the cavities of the permanent supply canals, where they occupy special cavities, the ampullaceous sacs. The cells of the ccelomatic cavity are flattened and similar to those of the ectoderm. The meso- derm is very thick, and the canals radiate with great regularity from the cavity of the sponge to the exterior. The outer part of each canal $ represents the supply, and the inner, the drainage system. The spic- Fie. 56. —Scycan- : . A ‘ dpaveiliain. wes are usually in two rows, their radiated bases being turned, respec- tively, inwards and outwards. While the living species are some- what numerous, but one fossil genus is known, and this is of Jurassic age. SPONGES. 63 SuB-ORDER III. — LEUCONEs. The higher position of this group is shown by its greater complexity. The meso- derm is thicker than in the last sub-order. The canals of the supply system are irregu- larly branched and frequently anastomose with each other, forming cavities near the outer surface. The collared cells are distributed along the smaller canals in the lower forms, while in the higher they are confined to the ampullaceous sacs. The Leucones represent the massive growths of the Keratosa and Silicea, but usually have a common or united cloacal aperture and are composed of consolidated tubes. Zittel considers this group a lineal descendant of the next, a view which does not seem to be justified by the morphology or the mode of development of the individuals of the group. No fossil forms are known. SuB-ORDER IV.— PHARETRONES. This division was established to contain a number of forms which occur as fossils in the rocks between the Devonian and the end of the cretaceous period. The author is inclined to consider the genus, Zrichonella, which is represented by a species in Australia, as a living member of this group. The spicules are so united as to form irregular threads, and sometimes a very intricate network. The canal system was branching and irregular, while the mesoderm must have been very thick. Cuass II. —CARNEOSPONGLAE. With increasing knowledge the multitude of forms comprised in this class will doubtless be separated. The common characters are a very thick mesoderm, the ecto- derm and endoderm similar to that of the Leucones, and the supply and drainage system as described above in the commercial sponge. The skeleton may be either com- posed of horny material (keratode) or partly or entirely of silicious spicules. The skeletal elements are radiately or irregularly arranged according to the plan of canal system which it supports. One order has no skeleton, but the form and structure show it to belong to this class. OrvErR I.— HALISARCOIDEA. This order, which Haeckel calls Myxospongiz, embraces but a single genus of fleshy sponge, known as Halisarca. One species is common on our shores, and also on those of northern Europe. The animals grow usually in flat masses or little bunches of a dull color, coating rocks or surrounding the stems of marine plants. The general structure can be seen in Fig. 49. With a fleshy nature, of course no fossils of this order can occur. Ornper II. — GUMMININ Z. These are tough and leathery sponges, the external layer forming a cortex which is partly composed of fibres, which also permeate the central mass surrounding the canals, and also penetrate the mesoderm. Their composition is still unknown. The genus Chondrilia has star-shaped silicious bodies in the cortex which are not found in Gem- minia and in the other genera. No fossils are known. 64 LOWER INVERTEBRATES. Orper III. — KERATOIDEA. These are the true horny sponges, and from an economic point of view, are the only ones which have any practical value. The skeleton consists of fibres of sponge- horn or keratode, forming a network in the mesoderm. They are littoral forms not usually found in water more than seventy-five fathoms in depth. They generally avoid sandy or muddy localities, preferring rocky ground or coral reefs. Passing by the genus Darwinella, for which a sub-order has been formed, we come to the sponges of commerce. SuB-ORDER J. — SPONGINA. The Sponginz are characterized by having the fibres of the skeleton solid, but in places where the water is filled with floating matter, they usually have a core of foreign material, a fact which we have previously mentioned. The marketable kinds are all of one genus, Spongia, that from which all the sponges derive their common name. There are only six species with, however, numerous varieties, which are offered for sale, and in fact these may be reduced to three species, if one so chooses. Three of the species are from the Mediterranean and the Red Sea, and three from the Bahamas and Florida. Other species of this genus have a very general distribution, but they are all confined to the equatorial and temperate zones within an area on either side of the equator which is limited by the isotherm or average temperature for January of 50°F. The Spongia gram- inea and Spongia cerrebriformis are occasionally used in Florida and Bermuda, but are not exported. The marketable sponges owe their excellence to the closeness, fineness, and resili- ency of the interwoven fibres of the skeleton. The Mediterranean appears to be particularly favorable to the production of specimens with skeletons possessing these desirable qualities in the greatest perfection. Those from the Red Sea are next in rank, while those of our own shores, though corresponding species to species with these and the Mediterranean forms, are coarser and less durable. Thus Spongia equina, the Horse or Bath Sponge of the Mediterranean, is finer than the Spongia gossypina, the Wool Sponge of Florida and Nassau, though it otherwise resembles it closely. Spongia zimocca, the Zimocea Sponge, represents in the Mediterranean waters the much coarser Spongia corlosia and Spongia dura, the Yellow Sponge and Hard-head, on the American side. Spongia adriatica, the Turkey Cup-Sponge and Levant Toilette-Sponge of the Mediterranean, answers to the finest though not the best of our sponges, Spongia tubulifera. . It is probable that the Red Sea and the Mediterranean were both colonized by sponges from the Caribbean Sea, and, strictly speaking, the six marketable species ought to be classed as three species with six principal varieties, differing from each other according to their habitat. This conclusion is borne out by the facts that the Caribbean Sea contains more species of this genus than any other locality, that no marketable sponges are found in the Indian or Pacific oceans, and that the differences in quality cited above are occasioned in these and other sponges with fibrous skeletons by any change from shallower to deeper water, or from water loaded with sediment to clearer waters. In each of these cases a finer sponge is the result, and this correlates directly with the fact that even in the Mediterranean the marketable kinds are found ‘Aroysy oSuods uvryemyeq SPONGES. 65 in waters which are probably very rarely reduced, even during the month of January, to 55°, and perhaps for the best qualities not below 60° F. Marketable sponges are found in the Mediterranean on the coast between Ceuta on the African side, and Trieste on the Adriatic. None are found in the Black Sea, on the coasts of Italy, France, or Spain, or the Islands of Corsica, Sardinia, the Balearic Islands, or even Sicily. The species do not usually appear in water deeper than thirty fathoms. They are gathered by means of hooks on long poles, or directly by the hands of divers, or, as in the case of some of the coarser kinds, dragged up roughly by dredges. When secured they are exposed to the air for a limited time, either in the boats or on shore, and then thrown in heaps into the water again in pens or tanks built for the purpose. Decay takes place with great rapidity, and when fully decayed they are fished up again, and the animal matter beaten, squeezed, or washed out, leaving the cleaned skeleton ready for the market. In this condition, after being dried and sorted, they aré sold to the dealers who have them trimmed, re-sorted, and put up in bales or on strings ready for exportation. There are many modifications of . these processes in different places, but in a general way these are the essential steps . through which the sponge passes before it is considered suitable for domestic purposes. Bleaching-powders or acids are sometimes used to lighten the color, but these, unless very delicately handled, injure the durability of the fibres. ' The first fossils which undoubtedly belong to this group occur in the carboniferous rocks, Carter having described a Dysidea from this period, but masses supposed to ‘belong to the Sponginz have been found in much older rocks. Sus-OrpER II. — APLyYSINZ&. These sponges have a skeleton composed of fibres which are hollow or filled with a soft, friable core, and there are no foreign materials introduced from the exterior. The fibres are not as elastic as those of the Spongine and generally are much larger and coarser. The sponges are dendritic or grow in sheets, often of considerable size. The skeletons are more open in structure than in the last sub-order, and frequently the fibres have a fan-like arrangement. No fossils are known. OrpER IV.— KERATO-SILICOIDEA. As the name implies, this division forms a transition between the horny and the silicious sponges. The skeletons are formed of solid keratose fibres and silicious spicules. SuB-ORDER J. — RHAPHIDONEMATA. In this group the spicules are of one kind only, usually with pointed ends, and are loosely arranged in the vertical and horizontal fibres of the skeleton, and covered by the keratode, though often but slightly bound together. The keratode is light-colored or transparent. This division is represented on our eastern coast by the well-known Dead-man’s-finger Sponge, Chalinula oculata. This is a bushy form, common on piles or rocks, especially in tide-ways where there is a considerable current of clear water. It sometimes grows to a height of two feet. The cloacal openings are small and irregularly scattered over the surface of the branches, while the pores are imperceptible to the naked eye. The color is brown, sometimes softened by a warm undertone of VOL. 1.—5 66 ‘LOWER INVERTEBRATES. pink. The fibres of the skeleton are light brown, and friable when dry. The fleshy parts disintegrate so readily after death that these sponges cannot be kept for any length of time even in the strongest alcohol. Tuba is another genus of this group. No fossils are known. SuB-ORDER II. — ECHINONEMATA. The spicules of the Echinonemata are of two or more kinds. The simple smooth or double-pointed ones usually lie in the fibre, the rough single-pointed ones, with a more or less expanded base, stand out from the keratode, leaving the point bare. Defen- sive surface spicules are often present. This sub-order is represented on our coasts by Microciona prolifera, which grows abundantly in the pools and tideways south of Cape Cod. When in still water and on a smooth surface it forms a thin, smooth sheet, but under other conditions it tends to grow up- right, and form branching masses a few inches in height. The color is a bright orange red, producing rich effects in pools where much of it is present. No fossil Echinonemata are known. Sus-OrpER III. — MonaActTINELLIN 2. In this group the fibres are composed of straight silicious spicules, while the amount of keratode is very slight. The most common form is the Crumb-of- bread Sponge, Halichondria panicea, which has a world-wide distribution, and occurs plentifully in a dried state upon our beaches. It is almost as light as dried bread, and when well bleached is very white. Another form, Suderites compacta, occurs on the coast south of Cape Cod, and is the only form in that region which is able to live upon the shifting sands. The pores are so small, and the structure so dense, that the sand cannot obtain an entrance, while its lightness keeps it from being buried. Specimens securely anchored have been found, and evidently the usual free condition is an acquired adaptation to a habitat on a sandy bottom. They are washed ashore in considerable numbers, and so fine and homogeneous are their spicules that the skeletons are said to have been formerly used for polishing silver. It grows in flattened masses of a yellow color, but the skeleton when bleached is white. Another species of this genus also frequents the sands north of Cape Cod, but finds more congenial accommodation on the shell of a species of gasteropod, nearly all of which, in certain localities, bear a sponge. Some of this group have accustomed themselves to lead a life of borers, and though not successful with hard rocks they are very destructive to the shells of various molluses, and even to limestone and marble. Cliona sulphurea, a very common form, is the most remarkable of these borers. It penetrates and excavates chambers in the shell of a mussel for example, and then, after causing the death of the animal, it will entirely enclose and resorb what is left of the shell. Not content with this conquest it Fig. 57.— Luba labyrinthiformis. > SPONGES. : 67 often proceeds to grow around stones, or to take in sand until its flesh is full of such indigestible ballast. Such specimens will sometimes be a foot long, and weigh several pounds. Occasionally this form is found attached in the usual manner, and when the locality is free from stones or sand the specimen is clean and free from such encum- brances. In the Mediterranean this genus plays no small part in the disintegration of the limestone rocks of the shores. It is evident that this sponge is a borer from inclina- tion and not from necessity, and also that the inclusion of sand.and stones is not needed, but is probably due to the effort to become attached to any object within reach. It is difficult to explain the boring except as a chemical process, but no one as yet has been able to detect any acidity in the secretions. It may be, however, that it is accom- plished by the silicious spicules on the surface. That they are not the sole means of boring is shown by the recent observations of Nassonow, who ascertained that the young began to bore before the formation of any skeletal structures. ' The Monactinellidan forms in the paleozoic rocks are uncertain, though Zittel records Cliona from the Silurian, and two genera in the Carboniferous. The first undoubted forms occur in the Jurassic. SuB-ORDER IV. — PoTAMOSPONGLA. The Fresh-water Sponges, in our opinion, form a group of sub-ordinal rank. The skeleton is similar to that found in the last group, but a very important difference is found in the reproduction. In these fresh-water forms there are found what are known as winter buds or statoblasts. These are protected by an outer coat of spicules of a peculiar form, wholly unlike anything else found in the sponges. They may be as simple as the spicules of the sponge skeleton, and arranged flatwise in the corneous wall of the statoblast, or they may be shaped like a collar stud (birotulate), and arranged vertically. There seems to be a definite line between these two types, and, in fact the sub-order has been divided into two families upon these characters, and named the Lacustridz and the Fluviatilide respectively. About ten genera have been described by authors from the fresh waters of all parts of the globe. They are usually green in color when exposed to the light, but when found under stones or in shaded localities are of a brownish hue. They have a decided affection for clean water and hard bottoms, being in large part attached to stones, logs or plants, but will grow sometimes on muddy bottoms. In such cases the young anchor themselves to small sticks or stones, and thus secure themselves from being choked by the mud. The sponge dies during some cold spell in the autumn, and their quick decay in large quantities is one of the principal causes by which the water supply of even a large city may be vitiated. They seem to be the cause of the peculiar smell known as the “cucumber odor,” and render the water extremely disagreeable as a beverage. The preservation of the species is accomplished by the statoblasts which retain their vitality through the winter, usually enclosed in the skeleton at the base of the colony. They develop in the spring, producing new colonies. Mr. Potts, of Philadelphia, aceounts for the large size and rapid growth of the sponges in the spring by the coalescence of numbers of the young which develop within the meshes of the same old base. This author asserts that he has repeatedly observed ‘that the young sponges from the statoblasts build upon the undecayed remnants of 68 LOWER INVERTEBRATES. the last year’s skeleton as if it were ‘a trellis, which, when once constructed, could be used repeatedly. This is not hard to believe, since two branches of the same sponge will unite if brought in contact, and even two sponges of the same species will not infrequently ‘combine to form a single specimen. A certain proportion of some of the fresh- water sponges does outlast the winter, and these old skeletal frames frequently contain many statoblasts. Certain of the fresh-water sponges in tropical countries have.to pass through a dry season, and it is supposed, with a considerable amount of probability, that their statoblasts can undergo dessication without loss of vitality, and even that they may be carried by the winds, thus — affording the starting points for colonies in new localities when the rainy season sets in. Some forms are described as having no statoblasts. OrpER IJ. — SILICOIDEA. This, the highest order of the sponges, is characterized by having the skeleton almost entirely composed of silicious spicules. SusB-ORDER I.—TETRACTINELLIN 2. This group can be represented by Tethya, in which the skeleton is radia. tory. The typical spicules have a long, straight axis and three curved arms, reminding one of an anchor, or more accurately, a grapnel. There are also long, straight spicules with both ends alike, and star-shaped silicious bodies. By the latter these sponges are allied to the Gumminine. Geodia is another remarkable type in this group, with ex- tremely thick and unusually large in- ternal spicules. When dried, these sponges are as hard as if carved out of wood. According to Zittel, the greatest authority on fossil sponges, this sub-order first appeared in the carboniferous, but was represented only by isolated spicules until the genus Geodia appeared in the Jurassic. Fic. 58. — Euplectella aspergillum, Venus flower-basket, SPONGES. 69 SvuB-ORDER II. ee, LITHISTIN.A. This group is composed of fossil forms in which the skeleton is made up of rather irregular star-shaped radiating bodies, firmly united. Thus, a very strong and solid skeleton was constructed, which has consequently been well preserved in the rocks. The normal form is a mass with numerous cloacal apertures of average size on the upper surface, but forms quite as often grow in vase-shapes, with the cloacal apertures on the inside, or like a pear, with the apertures on top. The large opening in the vase-shaped forms is usually described as a cloaca, though, as we have seen, it is not so in reality. The type appears in the genus Aulacopium of the Silurian, though Zittel thinks that some of the Cambrian forms may belong here. SuB-OrpeErR III. — HEexactTiInELLINz. The glass sponges are remarkable for possessing six- armed spicules. Two of the arms may be almost indefin- itely lengthened and bound together with others in threads closely resembling spun glass. In others they may be shortened and split into the semblance of flowers with narrow petals. The glass sponges remind the observer of the calcareous sponges, but the resemblance is merely superficial, and not so important as it at first appears. Though the Zuplectella is hollow and has apertures through the wall as do the Calcispongiw, they do not lead into radiating canals, but into areolar tissue and com- municate with the ampullze by means of numerous aper- tures in the walls of the sacs. The outlets of the sacs are large and open internally into the tube. The external and internal walls are supported by the interlacing arms of the crosses or hilts of the spicules, and as these are arranged with great regularity, the surface of the skeleton is divided into squares. The pores of the outer surface are usually situated one in each of the quadrangular intervals, and the cloaca occupy a similar position on the inner wall. The top of the sponge is closed with a network of threads, between which occur, as in Hyalonema, the true cloacal outlets. In fact Huplectella may be regarded as a hollow re Hiplenaron | a Hyalonema was at first known only by the stem which a was highly prized as an ornament. The natives were in the habit of cleaning off the sponge body from the upper part of the stem, and then reversing it in a suitable standard. It was sold to strangers as the skeleton of the parasitic polyps (Palythoa) which live habitually on the stem. Scientific men were at first deceived, and the true character was not discovered until 1860, when Max Schultze found the sponge tissues, 70 LOWER INVERTEBRATES. and showed that the polyps were but commensal parasites, having nothing to do with the formation of the long stem of silicious threads which resembles a plume of spun glass. Fia. 60. — Holtenia carpenteria. This genus may be expected in depths varying from forty to one hundred fathoms in northern seas, and in deeper water as we go towards the tropics, apparently requir- ing an average temperature below 40° F. The sponge itself in the natural state, is not as attractive as Huplectella, being of a light-brown color, and friable when dry. The top is usually occupied with a number of cloacal apertures surrounding a central prominence which is in reality the end of the stem. The stem is spun by the tissues SPONGES. 71 as a supporting column of elongated spicules bound together and growing in a spiral as the animal progresses upwards. The lower end of the stem becomes frayed out, and sinks into the mud as the ani- mal grows, but constant additions to the upper end compensate for this and form a column which sometimes reaches a foot in length. In Fig. 59 we see on the right a perfect specimen. The stem in the living sponge is always enveloped in the fleshy tissues. In Holtenia we have a different type of sponge, similar in shape to the members of the Calcarea, but the resemblance goes no further. The star-like beauty of the external covering of | spicules, and the singular profusion of anchor- ing threads which are formed below, are shown in the adjacent figure. Dactylocalyx is another | Za \ of the open vase forms which occur in this sub- ~; Or” yy ae order. oY ( } " f ) pr The fossils are very numerous, and it is 6 ab ep ¢ GY aa supposed that several of the Cambrian sponges H ( JI6\ ( [Re may belong here, though Zittel cites only cer- ye. ¢1.—Section of the outer wall of Ventriculites tain Silurian genera like Astylospongia and _ simplex, showing the structure of the silicious Protospongia as undoubted Hexactinellids. One of the best known of the fossil types is Ventriculites, our figures of which show, not only the general shape, but the structure of the skeleton as well. AtpHeus Hyarr. a <-_. Fia. 62. — Spicule of Pheronema. 72 LOWER INVERTEBRATES. Branco IIT. — COXLENTERATA. Tue Coelenterata embrace the jelly-fishes and corals, or more accurately speaking, the Hydrozoa, Actinozoa, and Ctenophora. In the first and last of these divisions fall most of those animals which are commonly known as the Medusz, while the Actinozoa include the true corals and their relatives. The endless variety of names which one encounters in this group need not lead to confusion, and if considered in the light of the historical development of the study, indicates those various characteristics which have from time to time attracted the attention of students of these animals. Of general terms used to designate the group, that of Zoéphytes is one of the oldest. In the infancy of natural science, when superficial observations took the place of more accurate anatomical studies, it is not to be wondered at that the likeness of these animals to plants led to the present name. One of the first comparisons which the novice makes, on seeing these animals for the first time, is that they resemble closely members of the plant world, and in maturer studies we are continually meeting similar resemblances of a deeper-seated nature The Celenterata include two of the large divisions of the Radiata of Cuvier, who first outlined their characteristics in the masterly manner which marks all his works as models of zodlogical research. The name Ccelenterata dates back over a quarter of a century (1847), to the profound investigations of these animals by Frey and Leuckart, by whom it was first used. The limits of the subordinate group of Hydrozoa are in many particulars obscure, and while many naturalists prefer to include in it a large group of gelatinous animals called the “ sea-lungs,” comb-bearing meduse known as Ctenophora, others, from the close likeness of their young to the larvee of the star-fishes, set these apart as a separate group. The Hydrozoa as here considered include the Hydroidea, the Discophora, and the Siphonophora, and contain by far the larger part of the true Meduse. The term Acalephe, common in many writings on these animals, is almost synony- mous with that of Hydrozoa as here used. By many it is also made to embrace the Ctenophora. The term was long ago used by Aristotle, and refers to the stinging powers which many of the Meduse have. Given by many authors a greater or by others a less extension, it has been wholly abandoned by most of the leading students of these animals. The Actinozoa or corals are marshalled under two divisions, the Actinoid, or true reef builders and their allies, and the “sea-fans” and “sea-whips,” which are called, from more or less fanciful reasons, the Halcyonoids. The single anatomical feature which is common to the groups mentioned above, to which, in point of fact, they owe the name of Celenterata, is the identity of a stomach and the body cavity. In the simplest forms these cannot be distinguished from each other, and in the higher genera there is but a slight differentiation of one from the other. J. WaLTER FEWKES. Se Gorgonia verrcosa, to which is attached a skate’s egg, natural size. HYDROIDS. 73 Cuass I.— HYDROZOA. OrprrR I.— HYDROIDEA. In the year 1703, that charming old scientific gentleman, Anthony Van Leeuw- hoek, of Delft, sent a very interesting paper to the Royal Society of London. In this article he tells us that “the water of the river Maes is brought by means of asluice dur- ing the Summer flood, directly into our town, and it is as clear as if the river itself ran through the town. With this water comes in also a green stuff of a vegetable nature, of which, in a half hour’s fishing, I got thirty pieces, and put them into an earthen pot together with a large quantity of their own water. I took out several of these weeds from the pot, one by one, with a needle very nicely, and put them into a glass tube of a finger’s breadth, filled with water, and also into a lesser tube, and caused the roots of the weeds to subside leisurely ; then viewing them with my microscope, I observed a great many and different kinds of animalcula. About the middle of the body of one of these animalcula, which I conceived to be the lower part of its belly, there was another of the same kind, but smaller, the tail of which seemed to be fastened to the other.” Our author, in the latter part of his article, assures us that he saw the smaller ani- malculum separate itself from the larger, and enter upon an independent existence; moreover, that he also determined by his microscope, the formation of a minute bud upon one side of the animalculum, which grew into an animal, perfect in shape, size, and all particulars, and then detaching itself from its parents, floated free in the water. That was the first discovery, so far as all the records give evidence, of the very wonder- ful animal, which is now called Hydra, and which in many respects, both in structure and in mode of life, is a very good type of its order, the Hydroidea, and at the same time of the class of Hydrozoa. The body of Hydra, which is entirely soft, having no skeleton without or within, easily changes shape, and when entirely contracted, has the appearance of a small dot or particle of gelatinous matter resting on the surface of the aquatic plant, chip, stone, or whatever may be the object in the water to which this small creature has attached itself. Watching it slowly expand in a dish of fresh water, it is seen to display a long, slender cylindrical body, which, in Hydra viridis, is bright green, while in H. fusca the color is light-brown. The base, or that end by which Hydra ~ fastens itself, is termed the disk or foot, and the éxternal cells of this part of the body secrete a gelatinous substance, which, hardening some- what in the water, enables it to attach itself at will. Toward the anterior or free end of the body, are a variable number of long, slender processes, the tentacles, which are arranged in a single circle or wreath. Within the ring formed by the bases of the tentacles, the body tapers to a rounded elevation, where the mouth is found, and this tapering eee portion of the body which extends beyond the retracted tentacles, is sponge ba known as the proboscis or hypostome. Within the body there is a cavity extending from one end to the other, from the base to the mouth, and, as these processes are hollow in Hydra, to the tips of the tentacles, Not only the body, but also the tentacles are very expansive and con- tractile, and seldom retain the same shape and position for more than a few minutes. e 74 LOWER INVERTEBRATES. When they are fully contracted they appear as so many knobs or bosses on the distal end of the body, and when fully expanded, I have seen them three and even four times the length of the fully elongated body. The tentacles are very sensitive, and if touched by some foreign object in the water, they rapidly contract, and the body also sharing in the contraction, the entire creature is withdrawn as much as possible from the area of disturbance and danger. Hydra has been observed in two or three rare instances to move from place to place by standing on its head, so to speak, using its tentacles as feet, by which it attaches itself, then it arches the body and attaches the foot-disk, releases the tentacles, straightens the body to arch it again, and so hitches along like a measuring-worm or geometrid larva. Another very peculiar form of loco- motion is described by Marshall, of Leipzig, as seen by him in certain Hydre found in brackish water. In this case the Hydra lies upon one side, and uses two tubercles as large, lobate, pseudopodial processes which give a creeping motion to the creature. Every one who has watched Hydra in aquaria has probably seen it creep or glide slowly over the surface of a leaf or of the glass. It keeps its normal position, attached by the foot-disk, but glides slowly, and with a very uniform motion, over the surface to which it is attached; much as a snail creeps, only with a much slower movement. This power of changing place is due to the cells in the foot-disk. Watching under a microscope, this part of Hydra, when it is in motion, it will be found that the external cells throw out pseudopodial processes, which extend in the direction in which the animal is travelling; so that Hydra can move by pseudopodia as truly as Ameeba does. In the position which Hydra so often assumes, that of complete expansion with the tentacles extended to their utmost, and forming a very large circle, its chances for getting food in the well-populated, often semi-stagnant waters in which it is so frequently found, are very great. Any luckless crustacean of small size, such as Cypris or Daphnia, that happens to strike against one of those delicate tentacles is pretty sure to be used as food by the Hydra. The tentacle against which the crus- tacean has touched, curls around him, and after a few struggles his limbs fall power- less, and he acts as though it had been paralyzed. This peculiar paralyzing or stupefying effect is caused by the action of certain sting- ing or cnidocells (also called lasso-cells), which are most abundant in the tentacles, but are also found in other parts of the body. Each one consists of a comparatively large body-part, from which stretch away interiorly one or more slender protoplasmic processes to con- nect with a deeper layer of the body-wall; on the outer end of the cell is usually found a small proto- ( plasmic process which projects into the surrounding , water, but is too small to be seen with the unaided eye; this latter process is termed a enidocil, and probably receives and conveys stimuli from the ex- ternal objects to the cnidocell; within the body of the cnidocell is the capsule, a more or less ovate a ag a Tytania lari; structure, consisting of an outer wall which is per- fect and complete, and an inner wall which is folded in upon itself at one end to form a tube, which for a very short distance is of some considerable diameter, and then decreases in size and forms a long, thread-like tube, coiled up in the cavity of the capsule; within the larger, shorter part of this tube, attached to its wall, are a number of recurved hook-like processes which vary in HYDROIDS. 15 number, shape, and position in different species; the remainder of the cavity of the capsule is filled with a liquid very similar to, if not identical with, formic acid. Now, when any stimulus brings a cnidocell into activity, it forcibly ejects the larger part of the tube by a process of. evagination or a turning of this part of the tube inside out, as one turns the finger of a.glove; this movement is quickly followed by the ejection of the smaller part of the tube in the same manner, by evagination. If the body of some animal has touched the enidocil, then that body is pene- trated by the thread-like tube, and also possibly by a portion of the larger tube with its recurved hooks, and then the formic acid of the capsule pours §$§/ / \------- into the tissues of the prey and produces the general paralysis above mentioned. This paralysis, of course, is not the effect of the formic acid from one capsule, but from many. Once used,the |WAQerS< le. capsule is useless, as the tube cannot be withdrawn into it again. Other tentacles also close B Cc around the prey, and b ‘i i DrOYs r . y FIG. 65. — Diagrams of enidocells; A, previous to emission of contents; B, their combined action it is first stage of emission; C, filament completely extended; a, wall of capsule; b, barbed sac; c¢, filament. conveyed through the mouth into the general cavity; here it may be seen, with microscopic aid, to break down and go to pieces, the products of the disintegration being a fluid, evidently a nutritive one, which then flows to all parts of the body, and the remnants of the hard chitinous skele- ton which are ejected by the mouth or through an opening which may be extemporized " anywhere in the wall of the proboscis. This form of Hydra in which it is unconnected with any other individual or zooid is termed the solitary condition. When the surroundings are favorable for its vegetative life, one usually may find one or more Hydre attached to the body of what appears to be a main stem or parent form. These attached or appended zooids have been produced by a process of bud- ding from the parent individual, and each one of them ultimately separates from its parent by a constriction at its base and becomes a free and independent solitary Hydra. A bud starts as a small, rounded swelling on the side of the body; the swell- ing being hollow, and its cavity being directly continuous with the general body-cavity .of the parent; by ordinary growth it attains considerable size, and from its distal end a number of small swellings or prominences appear, which elongating, develop into tentacles; the portion of the bud anterior or distal to the tentacles becomes the pro- boscis or hypostome, and a mouth is formed in its distal end. Being structurally com- 76 LOWER INVERTEBRATES. plete, it catches and digests food, and performs all its functions while still attached to its parent. After a time a constriction separates it from its parent, but the opening at a Tl Fia. 66. — Longitudinal sec- tion of Hydra, greatly enlarged; a, tentacles; c, body cavity; e, ectoderm; n, endoderm; m, mouth; 8, supporting lamella. its base never entirely closes (at least in some species), and is known as the porus abdominalis. It does not function as an anus, however, and cannot be so considered. Before the first bud is set free, a second one may appear, and even a third and fourth on the parent body. Moreover, a secondary bud may appear on the body of the first bud, a tertiary on the body of the second, and a fourth on the body of the third before the first bud has become free. This is known as the compound or colonial condition. Another method of increase which rarely occurs in Hydra is division or fission, in which the entire animal divides into two parts, each developing all the parts necessary to make it a complete Hydra. Trembley observed this method, Résel also witnessed it, and Marshall has seen three cases of it. In this country the process has been seen by Mr. T. B. Jennings, of Springfield, Ill. The wonderful power which Hydra possesses of reproducing lost parts was first discovered and made known by Trembley, of Geneva, in the first half of the eighteenth cen- tury. He determined that even a small piece of Hydra vulgaris possesses the power, under favorable conditions, of developing into a perfect animal. His experiments were very varied, and many of them have been often repeated with the same results, since his day. Baker repeated nearly all of them. The most remarkable of his experiments in this line, was the turning of the hollow, cylindrical body of a Hydra inside out; so that the inner layer which before did the digesting, now performed the functions of the cuticle, and vice versa. This experiment, which requires very skilful manipulation, has been, I believe, repeated but by one biologist, FP! 6) yj rams eee ane Professor Mitsukuri, of the University larued letters as in fig. of Tokio, Japan. In a limited region on the body of Hydra, just below the tentacles, there appear under certain conditions, small out- growths of the body-wall which prove to be the spermaries; in them being developed the spermatozoa. Lower down on the body, in another limited zone, larger, rounded swellings are developed, which are the ovaries. Just how fertilization is accomplished is unknown, but the egg having been fertilized passes through a morula stage in which the outer cells become prismatic, forming a definite membrane around the interior; a chitinous coat is devel- oped about it, and then there occurs a retrograde step, as the entire embryo fuses into a simple, non-cellular mass; within this mass a small cavity appears, the first formation of the body cavity. In this condition it remains quiescent for a time, and then the HYDROIDS. 7 outer shell breaking away, the embryo, still with a delicate shell around it, escapes into the water; a cleft appears in the body-wall, which becomes the mouth; the tentacles are developed, and the embryo bursting its thin shell, appears as a young Hydra. The development of Hydra is thus seen to be simple and continuous; there are no great or sudden changes such as occur in the life-histories of so many other animals. | There are a number of so-called species of Hydra found in the United States, the most common of which are a green one known as Hydra viridis, and a light-brown one called Hydra fusca. The latter often attains a much larger size than the former, and on account of its being much more translucent, is a better kind for study. They are found in slow or stagnant water, and are sometimes so very abundant as to form a delicate, fringe-like covering over every submerged object, in quite a large pool. Hydra has also been found once in a brackish arm of the sea in Germany, by Marshall. Having obtained a general idea of one hydroid, we may now take up the systematic arrangement of the group, considering the various sub-orders and a few of the most prominent families. Sus-ORDER I. — ELEUTHEROBLASTEA. This, the lowest sub-order, has for its type the genus Hydra, which has already been described at length. No other genus belonging to this group is known. This sub- order is destitute of a hardened body-envelope, and the zooids of the body, or troph- osome, are never firmly attached. Even more simple than Hydra is the peculiar genus Protohydra found by Greef in the ocean at Ostend, Belgium. It can be best described by saying that it closely resembles Hydra, except that it entirely lacks the tentacles so prominent in that form. It reproduces by transverse fission. So little is known of the structure and growth of Protohydra that the position which it is made to occupy in our classification must be regarded as provisional. Sus-Orper IJ. — GyMNOBLASTEA. All the members of this division have a hardened body-envelope called the perisarc, and live in colonies which are always attached to some foreign support. From the next division of the same rank, they are separated by never having the reproductive and nutritive portions enclosed in a chitinous capsule, and the generative zooids do not usually become free, independently developing organisms. The generative zooid, escaped. from its parent, may have a medusa form, from which ultimately a large number of ova are dropped, or it may assume the condition called the actinula, an oval body floating passively about or creeping on the bottom. In those hydroids which have an actinula this body develops directly, without intermediate metamorphosis, into a hydroid of the same form as that from which it sprung. In some of the gymnoblastic hydroids there are no free meduse and no actinule, properly so called, but a locomotive zooid, called a sporosac, which performs the same function. The sporosac is a ciliated body, capable of active locomotion, and possessed of two tentacles. It carries in its cavity asingle ovum. In many of the young gymnoblastic hydroids, the embryo leaves the mother’s care as a planula, which develops directly into a hydroid similar to that from which it originated. With this sub-order a new feature is introduced. In Hydra we found the nutritive and reproductive systems united in the same individual, but here we find certain por- 78 LOWER INVERTEBRATES. tions of the colony set apart for the capture and digestion of food, while other portions have for their only function the perpetuation of the species. It must be remembered that the following account is a general one, and that there are many exceptions to it, some of which will be subsequently mentioned. We can best understand the structure of a colony by following it briefly in its development. From the egg there hatches out an elongated young, known as a plan- ula, which freely swims by means of the cilia with which the sur- face is covered. This finally attaches itself to some submerged ob- ject, loses its cilia and begins to develop the true hydroid condition. Around the upper (free) end appear the rudiments of the ten- tacles, while the base Fia. 68, — Development of Eudendrium; a, free-swimming planula; b, about to be . eas attached; c, d, attached; e, beginning of hydrorhiza and hydranth. begins to divide up and send out processes. These latter grow and ramify in a manner strikingly like that of the roots of a tree, and produce what is technically known as the hydrorhiza. From this root-like portion other individuals or zooids develop, some of which are like the first, and from their greater or less resemblance to flowers, are called hydranths. These hydranths form the nutri- tive portions of the colony. They may be cither stalked or sessile upon the hydrorhiza. Other zooids are also developed from the hydrorhiza or from the hydranth itself, but these never possess the tentacles and digestive organs of the hydranths, but have only reproductive functions, and are called gonangia. In these latter are devel- oped small zooids which in some cases become free, in others they never separate from the parent. These medusz or medusa-buds develop the male and female elements (eggs and spermatozoa) which in turn produce other colonies similar to that de- scribed. Here some very interesting questions arise, the most prominent of which is what constitutes an individual? From a single egg there is developed a number of zooids from which there escape quantities of medusx, which are frequently capable of feeding and of reproduction. Are each of these jelly fishes, reproductive sacs, and feeding portions to be regarded as separate individuals or as parts of one individual? The latter is the true course; an individual embraces all the products of a single egg, and the name zooid is applied to the various more or less independent portions, which, whatever their form may be, arise by budding or fission, but never by a new ovarian reproduction. This distinction is somewhat different from that found in the sponges. In a number of places in Europe and America, there has been found, besides Hydra, another hydroid, living in fresh or brackish waters, known as Cordylophora lacustris. It is a compound form, attaining a length of two inches in good specimens, and is usually attached to some water-weed or to the stones in the bottom of a stream. I have seen it flourishing in a stream where the current is very swift. Again it has been HYDROIDS. 79 found in an old well. These two, Hydra and Cordylophora, are the only hydroids « known to live in fresh-water. A third, imperfectly known form, allied to Cordylo- phora, has been described by Professor Cope, from a lake in Oregon. In the oceans, hydroids are very abundant, and there are at least several hundred species. All of them may be arranged in a few groups, most of which are represented on our shores. Our first example of the marine forms will be Clava leptostyla, a beautiful reddish species which occurs on our coast from Long Island Sound northward. Its most common habitat is at or near low water mark, attached to the rock- weed (Fucus), where it forms colonies consisting of numerous individuals attached to a common rhizome or branching base. It is about a half of an inch in length, and the “head” bears from fifteen to thirty irregularly arranged slender tentacles. Beneath the tentacles, at the breeding season, the small reproduc- tive buds are arranged in groups as shown in the figure. The reproduction is essentially like that of the next species. One of the most common forms found in shal- low water (one to twenty fathoms) from Vineyard Sound Fia. 69.— Cordylophora lacustris. northward, is known as Hudendrium dispar. It grows in colonies from two to nearly four inches in length, and the parts of the colony which correspond in appearance to the stems and branches of a plant are dark-brown or black. At the tip of each branch and branchlet is a hydra-like animal, or zooid, which is directly connected with every other one in the colony, for the whole colony is strictly comparable with a much-budded Hydra grown to an equal height, and the general cavity of the body is con- tinuous through all the stems and branches into every zooid. When taken out of the water, however, Hudendrium retains its shape, which Hydra cannot do. This stability or rigidity is due to the existence of a nearly complete coat or covering of horny material, chitin, which is secreted by the animal, and which extends over all the colony, with the exception of the zooids; they remain unprotected. During the summer months two kinds of Zudendrium may be found along the New Eng- land coast, which are exactly alike in the characters given, but differ in color, one having white zooids, the other yellow. A little careful examination will show that upon the bodies of the white zooids are a series of structures arranged in a circle just 2 beneath the tentacles; each one of these is in shape like a short ie string of beads, which are supposed to be male organs, showing Fig. 70.— Clava leptostyla, tot the white colonies are male. The yellow ones are colored enlarged ; a, b, c, d, me- dues bode. pupa by a number of simple bud-like processes which are irregularly scattered on the body of the zooids; they are the female reproductive organs or ovaries. In Zudendrium then, the sexes are in different colonies. An egg having been fertil- % 80 LOWER INVERTEBRATES. ized, passes through the process of segmentation, a cavity appears within it, then it assumes an elongated form, possesses a double wall about the central cavity, develops , cilia upon the outer surface, and breaking through the containing wall, escapes into the water where it leads a free life for a brief time (see Fig. 67). Before long it enlarges at one end, settles down, becomes attached by its larger end, loses its cilia, and proceeds to develop a new colony of Hudendrium in the following way: It en- larges at its free or distal end, and around this enlargement appear a number of smaller swellings which develop into a wreath of ten- tacles; a mouth forms in the extremity of the proboscis and a layer of chitin is secreted around the body. Then by the simple pro- cesses of growth, combined with budding, a new colony is formed quite like the one from which the germ came. In this case the medusa buds do not develop into free-swimming jelly-fishes, but discharge their reproductive elements without leaving the parent colony. i Parypha crocea, a beautiful hydroid of a bright red or salmon Fie, 71.—Eudendrium color, is very common along the whole New England coast, while oe er nea ae a closely related, if not identical species, extends southward as far meduscia Dude: as South Carolina. It attains a length, in favored localities, of five or six inches, and grows in great luxuriance on the piles of wharves or bridges, especially where the water is slightly brackish. The outer or lower circle of tentacles are long, and just within them arise the meduse buds resembling clusters of small, bright-red grapes. In each colony the sexes are distinct, and in these buds the eggs or spermatozoa are developed. The young escape in the actinula condition, and creep about, finally attaching themselves, and then by budding and branch- ing, large colonies are formed, which in turn produce medusa buds, thus completing the life cycle. Another common form on our Atlantic coast from South Carolina to the Gulf of Maine, is Pennaria tiarella. It grows in colonies equal in size or a little larger than those of Hudendrium, and is found at- tached to rocks and eel grass, and often to floating alg. The zooids are usually a roseate color, and the species is remarkable for its beauty. In general structure Pennaria is like Hudendriwm, but differs in hav- ing, in addition to the one row of large tentacles, a number of smaller capitate tentacles, arranged, more or less definitely in two circles near the anterior end of the proboscis; it also differs in its mode of branch- ing, and in its method of reproduction. In the summer months there may be found growing out of the lower part of the proboscis, one or more oval bodies which finally develop a deep bell-shaped body with a considerable opening at the free end, about which are a number of rudi- mentary tentacles ; within the cavity of the bell-shaped zooid is a pro- cess corresponding in shape and position with the clapper of a bell, it py. ie Buveh. is in fact the proboscis, and at its free end is the mouth. By means = ¢ieea, natural of a sort of gullet or cesophagus passing through the proboscis, the ‘ mouth communicates with the central digestive cavity located at the base of the pro- boscis in the upper part of the umbrella; from this central cavity four ducts at four J Tubularia indivisa, tubularian hydroid. ee HYDROIDS. 81 equidistant points stretch away to the rim of the bell, where they are all connected by a tube passing around the rim. By means of these gastrovascular canals nutritive mat- ter from the stomach is carried all over the body. Stretching partly across the open- ing into thie bell, is a thin, centrally-perforated membrane called the velum or veil. After one of these meduse has been completely developed on the proboscis of the hydroid of Pennuria, it is freed from the proboscis by a constriction which cuts in two the small peduncle by which it had been attached, and the medusa floats away free in the water. It is not left to the mercy of currents, however, but is provided with a rather peculiar locomotor apparatus. The cavity of the bell being filled with water, its mus- cular walls are powerfully contracted, and the water being ejected from the opening in the velum, the medusa is forced through the water in the opposite direction ; then expanding its bell by other muscles, it is ready to contract again and send itself still farther on its way. The tentacles and outer surface of the medusa are well supplied with cnidocells with which they defend themselves and kill their prey in the same manner as Hydra, and as the zooids in the hydroid colony. The meduse are sexual zooids, thé sexes being separate, and in the case of Pennaria, the male and female elements are developed within the walls of the proboscis. From a fertilized egg a planula is developed, which in turn gives rise to a hydroid colony of the Pennaria kind. The life-cycle is thus more complicated than in Hudendrium by the introduc- tion of the medusa stage. The length of an average Pennarta medusa is about one- sixteenth of an inch. Objects of more exquisite beauty than some of these hydroid-meduse do not per- haps exist. Each minute crystal chalice with its beautifully curved outline, elongated, delicate tentacles gently coiling and uncoiling, and its slender proboscis which hangs like a lamp in its centre, lighting it with a soft phosphorescent glow as it swims with most perfect grace at the surface of the ocean, is the very type of delicate beauty, suggesting the won- ders of fairy-land. The dredge frequently brings up delicate pink or flesh-colored hydroids consisting of single stems, each supporting a single hydranth. This hydranth bears two sets of arms, those around the free end of the proboscis being much shorter than those nearer the base. This form was called by Agassiz Corymorpha pendula. It lives with the base imbedded in the mud, and grows to a length of four inches. The investing envelope is very soft, and the animal is able to greatly modify the shape of the stalk and pro- boscis. The medusa buds never become free-swimming jelly-fishes, while the hydroid stem always bears a single head or hydranth, a 16,7} —Menocdulispen- fact which led Allman to refer it to the genus Monocautis. The genus Zubularia and the closely allied Zhamnocnidia, are represented on our coasts by several species. The hydranths are borne on slender stems, and form col- onies reaching sontetimes a height of eight or ten inches. Under a low power of the microscope, the beauties of the animals stand revealed, far exceeding the power of any pen to describe or brush to paint. The hydranth is surrounded with two circles of tentacles, and from between the lower ones the reproductive zooids hang down like bunches of grapes, or they cluster around the proboscis inside the outer circle of ten- tacles, so that it requires no very vivid imagination to imagine the whole a delicate fruit-dish filled with the most beautiful fruit. From these raceme-like clusters the VoL. I.—6 82 LOWER INVERTEBRATES. young come forth in an actinula condition, presenting distant resemblances to a jelly- fish. The body is long and surrounded by a single circle of tentacles. This larva soon becomes attached and then develops into a form like the parent. Many of the small spiral shells found in the shallow salt-water just below the water’s edge, are found to be inhabited by hermit crabs, which travel about very actively by protruding their legs from the aperture of the shell. On the backs of many of these shells is what appears to the eye, a white, delicate, mossy growth, covering most all of the shell, excepting that part which drags on the bottom as the crab travels. Under the microscope, this mossy growth proves to be a colony of very beautiful hydroids named Hydractinia. They live in colonies, but in- stead of forming a colony by branching in the ordinary way, the hydrorhiza, or part which attaches the colony, spreads out farther and farther, and sends up more and more buds, each one of which becomes a zooid, but which does not bud and is not covered by chitin. The hydro- rhiza is covered by a layer of chitin, and at irregular intervals the chitin is developed into a large projecting spine. The zooids are very contractile, and when withdrawn to their utmost, the hard chitinous spines pro- ject slightly beyond and protect them. Examining carefully the zooids of Hydractinia it is found that there are the ordinary feed- ing zooids, the reproductive Fia. 74. — Hydractinia yerrcgueiive venta” nutritive, b, female zooids, male and female, and a third kind which are destitute of true tentacles, have very slender, much elongated bodies, and are powerfully armed with strong batteries of cnidocells with which they perform their duty of protecting the colony. From a fertilized egg of Hydractinia is developed a planula, which in time gives rise to a Hydractinia colony. There are a large number of jelly-fishes known, which, from their structure, are classed among the Gymnoblastea, although nothing is known of their attached hydroid condition, or even if they pass through such a stage. HYDROID JELLY FISHES. Ou the left, Stomatoca apicata; on the right, Tima bairdii. HYDROIDS. 83 In the form known as Zizzia, it is the jelly-fish itself that produces the medusa buds. In our figure, which represents the young of ZL. octopunctata, may be seen younger jelly-fishes budding from the sides of the proboscis of the parent, and frequently in life, one can see still younger buds in these embryos before they free themselves from the parent. When arrived at a moderate size, these buds begin their contractions and struggles which finally end in their breaking loose from the parent, and the be- ginning of life on their own account. With age and increasing size, the tentacles grow much longer, those arising opposite the radial canals being in bunches of five, while those at the intermediate points are in threes, so that there are Fic. 75. —Lizzia octopunctata, young. thirty-two in all. Here also belongs the genus Stomatoca, with its two long, marginal tentacles, In. confinement our S. apicata seems to prefer the bottom of the aquarium, and but rarely comes to the surface. SuB-OrRpDER III. — CALYPTOBLASTEA. Nearly all the many species of Hydroids on the American coast which have bell- shaped hydrothece, belong to the large family CampanuLarw. One of the finest representatives in American waters of this family of hydroids is Obelia longissima. It lives in shallow water, and down to a depth of about twenty fathoms, from Long Island Sound to the Bay of Fundy. The colonies are often quite large, measuring eight to twelve inches in length, and are of great beauty; at the tip of each stem and branch is developed a zooid, and about the zooid is a cup of chitin, called hydrotheca, into which the zooid may nearly or completely retract itself, and out of which it may stretch and unfurl its single wreath of tentacles; the rim of the hydrotheca is cut into a number— twelve to sixteen blunt teeth ; the proboscis is very large and very mobile, constantly changing shape. In the axils of the branches are developed other chitinous cups (gonothecz) larger and always of a different shape from the hydrothecw, in each of which there is a long, simple zooid, destitute of mouth and tentacles (a blastostyle) ; on its sides are produced small buds, from eighteen to twenty-four, which develop into meduse. They are found escaping from the gono- theese from April to June. These meduse are sexual, and bear either male or female elements along the radial canals; each fertilized egg develops into a ciliated planula, and this gives rise to a col- ony of Obelia longissima. One finds certain points of difference between this medusa and that of Pennarta. The contracting wall which subserves the function of locomo- tion is not bell-shaped, but is nearly a flat disk, and tentacles exist all round the edge of the disk, there being from twenty to thirty, while the medusa of Pennaria has only 84 LOWER INVERTEBRATES. four rudimentary ones. On the edge of the disk, at equidistant points, are a number of globular bodies containing a cavity in which is a bristly ridge, and which is nearly filled with a clear liquid, in which are a few small calcareous particles that strike against the bristles when any disturbance in the water outside sets the liquid of the sac in motion. These are known as otocysts, and are supposed to be auditory organs. The meduse of Obelia longissima are very minute, measuring only one-sixtieth of an inch across the disk, and one-fortieth across the outstretched tentacles. Fig. 76. —Campanularian hydroid; u, 6, hydranths; e, hydrorhiza; /, gonangium; g, medusa. A less conspicuous but very beautiful hydroid of special interest, and belonging to the same family as Obelia, is represented by several species on the New England coast. They belong to the genus Gonothyrea, and, at a hasty glance, look like dimin- utive or young specimens of Odelia. In height they do not exceed an inch and a half or two inches; the hydrothece in the most common species, G. hyalina, are long, of very thin texture, and the rim is cut into numerous shallow teeth of castellated form. The gonothece spring from the axils of the branches, and contain a blastostyle upon which are formed a number of buds that develop in regular sequence from above downward; when the uppermost one is fully grown, it pushes out of the top of the HYDROIDS. 85 gonotheca, but still remains attached to the blastostyle by a slender peduncle ; this zooid is now seen to be sexual, and contains within the walls of its proboscis, the sexual elements; 0 the outline is nearly spherical, being cut off at the farther end where there is an opening into the cavity of the zooid; about this opening is a wreath of ten- tacles, and pendent in the cavity of the bell is a proboscis destitute of a mouth; the cavity of the blastostyle is directly contin- uous with a central cavity in this meconidium, as this kind of zooid is termed, and from this central cavity four radial canals pass out to four equidistant points on the edge or rim of the bell, where they all join a cir- cular canal; these meconidia never be- come free, but after discharging their contents, they die and disintegrate. The fertilized eggs develop into cili- ated planule which finally form col- onies of Gonothyrea hyalina. These meconids which are evi- dently meduse that never become free, are of great interest, being, in all probability, degenerate forms. Another large family, the Szrtv- LARID&, belonging to this same group, is represented in America by a beauti- ful species, Sertularia argentea, so- called from its light silvery color. The colonies are often a foot in height, and the shoots usually grow in clusters; the branches have a subverticillate ar- rangement, giving the colony an arbor- escent appearance. Ifasmall portion of a colony be examined with a magni- fier one discovers very peculiar hydro- thecee, which are very differently ar- Px at Fig. 77.— Gonotheca with meconidia of Gonothyrea; b, blasto- style; d@, gonophores in various stages of development; g, meconidia; m, ovum; o, embryos. ranged from any described above; they are nearly tubular, somewhat narrowed at the top, with pointed lips, and are either free or set into the sides of the stems and branches. 86 LOWER INVERTEBRATES. The gonothecw are developed on the branches and are elongated, somewhat urn- shaped, aperture central, termir.al with usually two, occasionally one long horn at the anterior end. The eggs are partly devel- oped within the gonotheca, and then pass into a sac which projects from the orifice of the gonophore, where they finally be- a come planule ; these after living a free \ NJ life become attached and form a new col- \ Z ony. Sertularia argentea is found from the New Jersey coast to the Arctic Ocean from low-water mark to a depth of over one hundred fathoms. It is very widely distributed, being found on both sides of the Atlantic and on the Pacific shore of the United States. Like many other Hydroids it is often col- lected as sea-moss andl is not infrequently seen at . the florists for decorative purposes. Another very common species of Sertularia is S. pumila, a very much smaller hydroid, not over one inch and a half long, and often found in abun- dance on the common Fucus or dark brown rock-weed. The hydro- yg. 79,4 frag- thee are opposite one pent of set another on the stem, giv- Tq oe ing it a compactness of structure and regularity of outline not possessed by S. argentea. The colonies are sexually perfect from May to Sep- tember on the New England coast. The method of reproduction is very similar to that of S. argentea. A third large family comprises the feathery forms known as the Prumurarip.t. They are represented on the New England coast by Plumularia tenella, Plumularia verrillii, and Aglaophenia arborea ; the last species was described by Desor in 1848, and has, I believe, never been found since. Other species of Aglaophenia and Phun- ularia are found on the Carolina coast, and,still others in the Californian waters. Perhaps the most elegant in appearance of all the American hydroids is the ostrich plume of our Pacific coast, Aglaophenia struthionides. It varies much in size and color, but always retains the appearance of a diminutive ostrich feather. Microscopic study shows that the hydrothece are arranged in a single row on one side of each branch or pinna, and that the branch is divided into very short joints, one to each hydrotheca. Each hydrotheca has its rim ornamented with a number of sharply FIG, 78. — Sertularia argentea, natural size, HYDROIDS. 2. P. tiarella, enlarged. 4, Eudendrium 3. Aglaophenia struthionides. dispar, male, enlarged. 1. Pennaria tiarella. HYDROIDS. 87 pointed teeth, and three minute tubular processes are disposed about its mouth, one on each side and one on the outer or anterior surface. These processes are termed nematophores, are filled with processes of the body substance, and in structure and development are believed by Hamann to give evidence of being degenerate zooids. Certain of the branches or pinne are at times replaced by cylindrical struc- tures which are covered with rows of nematophores, and are the cups or baskets in which the generative zooids are devel- oped; they are termed corbule, and in some genera are meta- morphosed branches, while in others they are modified pinne. A pinna is smaller than a branch, and differs from it in the character of the zooids formed upon it. The egg develops into.a planula, which becoming attached forms a new hydroid colony. These three great families, represented here by the genera Sertularia, Obelia, Gonothyrea, and Aglaophenia, are all mem- bers of a sub-order of hydroids distinguished by having the hydranths surrounded by chitinous cups, and the possession of longitudinal ridges in the body cavity. This group has been variously termed Thecata by Hincks, Calyptoblastea by Allman, and Inteniolata by Hamann. As among the Gymnoblastea, we find here medusee which agree in structure with those which are undoubtedly calypto- blastic, but of whose early development we know nothing. We can mention but one example. One of our larger jelly- fishes is Zygodactyla grénlandica, which sometimes acquires a diameter of even eleven inches. In color it is a light violet, with numerous brownish reproductive organs. The numerous tentacles which fringe the margin of the umbrella hang down a yard or more when fully extended. Concerning the habits of these animals Mrs. Agassiz has written: — “The motion of these jelly-fishes is very slow and sluggish. Like all of their kind, they move by the alternate dilation and contraction of the disk, but in the Zygodactyla these undulations have a certain graceful indolence, very unlike the more rapid move \\. ments of man QS Sy of the one y oe i, i | ii a | Fic. 81. — Zygodactyla grénlandica. 4 Fra. 80. — Corbula of Aglao- phenia struthionides, enlarged. It often remains quite i motionless for a long time and then, if \ you try to excite it by disturbing the ) water in the tank, or by touching it, it heaves a slow, lazy sigh, with the whole body rising slowly as it does so, and then relapses into its former inactivity. In- deed, one cannot help being reminded, when watching the variety in the motions of the different kinds of jelly-fishes, of the difference in temperament in human beings. 88 LOWER INVERTEBRATES. There are the alert and active ones, ever on the watch, ready to seize the opportunity as it comes, but missing it sometimes from too great impatience ; and the slow, steady people, with very regular movements, not so quick perhaps, but as successful in the long run; and the dreamy, indolent characters, of which the Zygodactyla is one, always floating languidly about, and rarely surprised into any sudden or abrupt expression.” Nothing is known of the development of this form, as all attempts to raise the eggs have proved futile, and it is unknown whether it has a hydroid stage or not. Sub-OrpDER IV. — TRACHYMEDUS.2. The Trachymeduse are usually considered a distinct group of Hydroidea, espe- cially characterized by having a direct development; that is, they are jelly-fish, which, in general structure, are like the meduse de- veloped from hydroid colonies, but their eggs develop directly into new medusz, and not into hydroids. They have then no hydroid state. They are represented in our waters by a num- ber of species, among them Trachynema digi- tale. The full-grown medusz of this species are from an inch to an inch and a half in length, the walls are very thin, and not much used for locomotion ; the latter function being performed principally by the muscular velum which pushes itself outward with considerable force. The proboscis is very large and has four lip-like ex- pansions about the mouth; the tentacles are numerous, and four garnet-colored otocysts are present at equidistant points on the margin of L RU CUA X the bell. The ovaries develop from the upper Wer parts of the radial canals, are cylindrical and much elongated, hanging pendent in the bell, and reaching nearly to the velum. Cunina, another genus of this group, though not so common as Zrachynema, is not rare on our coasts, where it is represented by two species, C. octonaria and C. discoides. An interesting fact in connection with these forms is that they live on Turritopsis, a jelly-fish allied to the Stomatoca mentioned on a preceding page. Fic. 82.— Trachynema digitale. SuB-ORDER V.— HyDROCORALLIN A. Among the many creatures that contribute to the building of a coral reef, are to be counted certain hydroids. For many years there was no suspicion but that the Mille- pore corals were built by true coral polyps. Professor Agassiz discovered their true nature twenty-five years ago. Later, some other coral-making hydroids have been thoroughly studied by Professor Moseley, of Oxford, late of the “ Challenger” expedi- tion. They are very beautiful forms, and there are three kinds of zooids; the ordinary feeding forms, the reproductive kind, and the dactylozooids. The latter have no mouth and gastric cavity, and possess only a tentacular function. JELLY-FISHES. 89 These forms, represented on our southern coasts by Millepora alcicornis, form a coral which, however, is composed of calcareous fibres and is traversed in all directions by canals. The little cups occupied by the polyps are shallow, but as one polyp dies another succeeds it, forming a partition separating the new cup from the old, so that in time the pits of the coral become deep but are divided up by a series of transverse partitions. A similar structure exists in some of the true. corals. Among the fossil forms referred to, the hydroids, the Graptolites of the Silurian period are most prominent. In these forms we have an approximation in general appearance to the Sertularian. These, so far as we are able to discover their anatomy, consisted of a narrow tube bearing, on one or both sides, a series of hollow teeth, through which the tube communicates with the exterior. It is supposed that each of these teeth was occupied by a zooid similar to that found in Sertudaria or Plumularia. Haeckel has described, from the lithographic stone of Solenhofen F1¢ ee a (Jurassic age), two fossil medusx, which he refers to the ; Trachymeduse, and from later beds portions of the incrusting hydrorhiza of Hydrac- tinta have been found, and true Sertularians occur in the pleistocene of England. Other forms referred with more or less doubt to this group occur in the Cambrian, carboniferous, etc. SamvuEL F. Crarkez. Orper II.— DISCOPHORA. Among the Meduse which attain the greatest size and probably are the most commonly observed are those called the Discophora, “sea-nettles,” “sea-blubs,” or “ jelly-fishes.” The members of this group are very characteristic, and are named from the disk-shaped outline of their bodies. Although the group of Discophora is not a large one, there being barely a half dozen genera found in our waters, it presents some of the most interesting features of all the known Meduse. The bodies of all the jelly-fishes are very gelatinous, composed for the most part of water, and when taken from their native element speedily melt away, leaving a thin film behind. Although these animals are not the only ones which have gelatinous bodies, they excel all in the amount of fluid in their tissues, and are consequently among the most transparent of animals. The habits of the Discophora are very curious. Many swim at or near the surface, sometimes protruding their bodies a little out of the water. Some are confined to the deep seas and are drifted only by accident into shallow waters. A rough sea sends many below the reach of the agitated waters, and in a calm they rise to the surface, to come into the range of the sun’s rays. Whatever their purpose is in this latter habit, we may trace to it the name of “sun-fish,” which they bear in some localities. Most of these animals in their adult condition are free swimming, while many are attached to the ground in their younger stages of growth in a way which will be treated of in our account of the development. Cassiopea is attached in the adult state in the following peculiar manner. This genus is very common along the Florida reefs where, instead of swimming about in the water, it lies at the bottom on the coral sand, lazily flapping its disk in a monotonous manner. It is not firmly anchored to the bottom, yet rarely changes its position any considerable distance. 90 LOWER INVERTEBRATES. Probably all are marine and many genera gregarious, either seeking each other’s company, or huddled together by ocean currents or tide eddies. At spawning-time they are said to don brighter colors, or at least their ovaries and spermaries at that time become more highly colored. Like the hydroids, their organs for defence and offence are the stinging-cells by which their bodies are covered. Many sting with great violence, while others can be handled with impunity. None, however, are destitute of stinging-cells. All are phosphorescent, especially when irritated, while the color and intensity of the emitted light varies with the genus. One of the most common Discophores in New England waters is called Cyanea, and is a representative of a family of moderate size known as the Cyanep.c. The most striking peculiarity of Cyanea is its disk-shaped body, which varies in size from that of a penny to several feet in diameter. Its color is reddish brown, but when dead and washed about for some time it becomes light blue. The body-disk is divided into two well-marked regions, called the aboral and the oral, or the upper and lower surfaces as the animal naturally swims in the water. The upper surface is smooth and without appendages, save little filaments which are remnants of bodies of considerable size in the young of the animal. The under or oral surface is so called from the fact that from it hangs not only the stomach with its mouth, but also many other important structures. The thickness of the disk in its centre is much greater than at the periphery, where it becomes very thin and flexible, and capable of considerable motion. Around the margin of the bell are found at regular intervals eight sense-bodies, which lie in deep incisions in the rim. Each sense-body is a small sac or cyst mounted on a short peduncle, and in the interior there are a number of rhombohedral otoliths of calcareous composition. Each sense-body is covered by a thin, gelatinous wall stretched above it, which is known as the “hood.” From the existence of this hood in the Discophora, and its absence in the Hydroidea, Siphonophora, and a few other jelly- fishes, these animals are called the hooded-eyed meduse, while the latter are sometimes, especially in older writings, designated the naked-cyed jelly-fishes. The most prominent of the several appendages which hang from the oral surface of the disk is a thin, curtain-like body of great breadth, which is thrown into a great number of folds and frills. This curtain is open below, and its inner walls make the walls of the stomach. It hangs far down below the oral surface of the bell, extending far beyond it as the medusa, by strokes of the margin of the disk, is driven along through the water. The tentacles of Cyanea are found in bundles, in each of which there is a great number of these organs. Each tentacle is long, thread-like, and very contractile, possessing stinging cells which, however, are rather feeble in their action in the genus Cyanea. The tentacles in larger specimens of the genus reach an extraordinary length, and, as in other Discophora, have for their function the capture of the food. The genus clwrelia, the type of the family AURELMD.x, is, next to Cyanea, one of the most common representatives of the Discophora in New England waters. Although it never reaches the great size attained by the former, it may well be ranked as one of the largest of our Acalephs. “YSsg-Ayal ourpesoo ‘nsopu0sf nadoissp) JSELLY-FISHES. 1 The body of Aurelia, like that of Cyanea, is disk-shaped, but has a creamy-white color. There are in this genus as in the last, eight marginal sense-bodies, each covered by a hood to which reference has already been made. A great difference between the two genera is in the development of the appendages to the oral side of the body, and instead of there being eight clusters or bundles of tentacles as in Cyyanea, there is in Aurelia a simple continuous cirele of short filaments set around the disk-margin. The tentacles are relatively much smaller than those of Cyanea. One of the most important characteristics of Aurelia is to be found in the structure of the mouth and oral appendages. Instead of a curtain hanging down from the middle of the disk, the mouth of Aurelia is formed in the following manner. From the central region of the oral surface of the disk the oral appendages are suspended by four gelatinous pillars. Between each pair of these pillars there is a circular opening which communicates with a central cavity in which the sexual organs lie. Below the sexual openings the pillars fuse, forming a gelatinous ring surrounding the mouth and serving as a basis of attachment for certain organs, developments of the lips, called the oral tentacles. These oral tentacles are four in number, and are commonly carried extended radially from a central mouth-opening. Each oral tentacle has no resemblance to a marginal tentacle such as is found on the edge of the disk in Cyanea or Aurelia, but is short and thick, smooth above, and bearing on its under side a deep groove which extends the whole length of the oral arm from its distal tip to the central mouth. On the ridges which enclose this groove are found at intervals peculiar, small, suctatorial mouths. The entrance to the stomach or the large mouth in Avwrelia is centrally placed on the oral side of the disk, and communicates directly with a disk-shaped cavity, the stomach, which lies directly above it. The lower floor of the stomach is formed by the oral surface of the bell, 2 muscular layer, from which the four cylindrical bodies which support the oral gelatinous ring are suspended. The roof of the stomach, or the gelatinous wall of the bell, 1s continued just above the mouth into a pyramidal jelly-like projection, which, however, does not protrude outside the mouth-opening. , The marginal sense-bodies of Awrelia are accompanied on either side by a gelatinous extension or lappet which extends outward and hangs slightly downward. On the aboral surface of the bell, in the neighborhood of the hood which covers the sense-body, there is a raised circular area of doubtful function which is not found in the vicinity of the sense-organs in Cyanea. This disk is called the sinnespolster, and is, as its name signifies, probably an organ of sensation. Of the many extraordinary genera of Discophorous meduse, one of the most peculiar is the genus Cassiopea, especially a species called C. frondosa found about the Florida Keys. This we may consider as the type of the family Cassioprip#. Apart from its curious habitat, being attached to the coral mud as has been mentioned above, it is remarkable in the peculiar arrangement of the complicated oral appendages which, although differing greatly from similar organs in the two genera already mentioned, are typical of several of genera belonging to the same great group. Cassiopea frondosa is found lying upon its aboral surface on the mud near coral islands in Florida and elsewhere in tropical seas. As one floats in a boat over these curious jelly-fishes, they look very similar to an algous growth on the sea-bottom, and are easily confounded with some of the forms of corallines which abound on the neigh- boring sheltered submarine banks. If, however, the medusa be closely scanned, it will be found to move portions of its body voluntarily, and a throbbing or vibration, espec- 92 LOWER INVERTEBRATES. ially of the edges of its disk, can be plainly seen. Although fastened to the ground, it still keeps up a flapping motion of its bell probably for purposes of breathing, just as is the case with free-swimming animals of closely allied genera. One of the functions of the marginal tentacles of the Discophora is the capture of the food. They wind themselves about their prey, sting it to death, and then, by con- traction, draw it to the mouth. In a medusa which is fastened to the ground, tentacles would seem to be necessary if the food was large and capable of movement. The con- struction of the mouth of Cassiopea shows that its food is of very small size. The medusa feeds upon the animal and plant life which drifts past it, or which is caused to move over it by the slow flapping of the bell margin. It is therefore evident that ten- tacles would be of little service to an animal with this mode of life, and accordingly we find its bell margin is wholly destitute of those filaments called tentacles, which form such a prominent feature in the adults of Cyanea, Aurelia, and several other genera. Throughout the animal world there are several examples which might be cited of animals which upon becoming attached to the ground, after a free larval existence, having no use for well-developed sense organs, lose the same or suffer a degeneration in their complication. This can well be illustrated in the development of some well- known genera of Ascidians, where the free larva has higher affinities throughout than the adult, and where a highly-developed organ of sense is formed in a larva to be lost in the fully-grown animal. The organs of sensation on the margin of the bell in Cas- stopea are, however, as highly developed as in any of its relatives which swim freely in the water. Abnormal as its mode of life is, the otocysts, or organs of sensation, found on the rim of the bell, have not disappeared, neither has their number diminished. In Cassiopea there are sixteen of these bodies in normal specimens, and we also often find monstrosities by which this number is increased to eighteen. Professor Agassiz found twelve of these structures in Polyclonia, a closely related or identical genus. The structure of the mouth of Cassiopea is somewhat as follows: In the centre of the oral surface of the bell there is a gelatinous cylinder in which there is a central cavity, but no external opening, in a position which corresponds to the mouth of other Discophora. On the side of this cylinder, however, there are openings, four in num- ber, leading into as many cavities partitioned by a thin membrane from the main cavity in which the sexual products are formed, and perhaps through which they pass when mature. From the oral cylinder there arise eight long arms which are commonly extended at right angles to the cylinder parallel with the lower floor or aboral side of the bell. Their tips extend a little beyond the bell margin, while the side adjoining the bell is smooth. Each appendage is branched, and from its aboral surface there is formed a great number of curious appendages of various functions. Two kinds of appendages can be recognized. The former are simply little feeding mouths sur- rounded by a circle of tentacles and resembling little Hydra. Of these there are a large number on the oral appendages, and each and all open into a system of vessels which pass through the appendages, and ultimately pour their contents into the cen- tral cavity of the oral cylinder. All of these Hydra together make up the mouth of the medusa, for they are the orifices through which food is taken into the stomach. The second prominent appendages to the oral arms are small, flask-shaped, and ovoid bodies, with a central cavity which opens into the vessels passing through the arms. They are, however, without an opening into the external water, and their true func- tion is not yet definitely known. A most interesting family, the PrLacipa, is represented in our waters by two genera called Pelagia and Dactylometra. In Pelagia we have a spherical-shaped JELLY-FISHES. 93 medusa of pinkish color and eight marginal sense bodies, alternating with as many ten- tacles on the bell margin. From the under side of the bell the oral appendages hang far outside of the bell cavity, resembling in many particulars the oral tentacles of the genus Aurelia. Pelagia is not a large medusa, and is very remarkable in its develop- ment, as will be explained more at length later in our account of this part of the subject. Dactylometra is closely allied to Pelagia, but has a larger number of tentacles around the bell rim. The sense body of both these genera differs in important particulars from those of the families already described. Fia. 85.— Dactylometra quinquecirra. Fic. 86.— Pelagia cyanella. The aberrant families of the Discophora are among the most wonderful of this group. A mention of a few of these may not be without interest. One of the most abundant meduse at times in the neighborhood of the Florida Keys is a Discophore, called by naturalists Linerges, and known to fishermen there as the “thimble-fish,” “mut- ton-fish thimble,” and by similar designations. Under proper conditions the number of individuals of this strange genus is very great, and they may be often seen extending in the water in long lines, where they are thrown by the tide-eddies and ocean currents. The popular name of thimble-fish designates exactly the form which these meduse assume. The bell is not unlike in size and shape a common thimble, differing consid- erably in this respect from that of the other jelly-fishes of the Discophorous type. The bell has a brownish color on its lower floor, and its walls have a bluish tinge. Around the bell margin there are sixteen marginal lappets or rounded lobes, between which, alternating with each other, there are eight rudimentary tentacles, and the same num- ber of marginal sense bodies. Each sense body is covered by a gelatinous extension of 94 LOWER INVERTEBRATES. the bell walls of such a form that when looked at above, it seems more like a cyst sur- rounding it than a hood serving as its cover. From the inner walls of the bell, hanging into the bell cavity, there are placed sixteen dark-brown pigmented bags which lie in a circle with a radius about one-third of that of the bell. Although the function of these bodies is unknown, it may be predicted that they will be found to serve as receptacles for the elaborated food eaten by the medusa. The stomach of Linerges is very simple in its structure and never hangs outside of the cavity enclosed by the bell walls. While the jelly-fish is in the act of swimming, the marginal bell lappets are commonly folded inward, forming a notched veil which distantly resembles the so-called velum of the hydroid medusa. At one time in the his- tory of the nomenclature of the jelly-tishes, the presence or absence of a veil was used in designating the two great groups into which the meduse were divided. The term Craspedota refers to those in which a well-marked velum is found, the Acraspeda where the same is absent. The Hydroidea and Siphonophora are craspedote, the Dis- cophora are supposed to be destitute of a veil, and are therefore acraspedote. Of the many aberrant families of the Discophora, none differ more widely from the genera which we have already considered, than that of the LucerNaripa, or CaLycozoa as they are sometimes called. In Lucernaria, the best known genus of this family, we have a trumpet-shaped animal of comparatively small size, which is attached by the smaller end, but has the enlarged extremity free. The free end has a disk-shaped form, and in the centre there is an opening into the body cavity which is the stomach. Around the edge of the disk there are arranged at intervals eight bundles of short tentacles or tentacular bodies of doubtful function. The body walls of one of our common species has a greenish color. Several theories of the relationship between the Lucernaridwe and the other Discophora have been suggested, and their relations to this group are not recognized by all naturalists. Of these theories there are two which seem to the writer the nearest approximations to truth in regard to the affinities of the family. Several naturalists, considering the attached mode of life of Lucernaria, but more especially its anatomy and what little is known of its development, have supposed that Zucernaria is in reality an adult in an arrested form or stage of development, and that its nearest ally must be looked for in the young of other Disco- phores. The young of many genera pass through a condition in the Fre. 88.—Lucer- progress of its development when it is attached to the ground, and Erheratt wnat the allies of Zucernaria are by many naturalists recognized in these forms. A second interpretation, suggested by E. Haeckel, has even more plausibility than that already mentioned. It has this in its favor, that it refers the Zucernaria to the adult and not to the young of another genus. A beautiful medusa was found by A. Agassiz and by the Fish Commission in the Gulf Stream, and has been referred to a genus long ago described under the name Periphylla. Periphylla is in fact a type of a family called the PERipHyLiip#, and is in many respects one of the most aberrant of the many genera which make up the Discophora. Poh FIG, 87.— Linerges mercurius, thimble fish. JELLY-FISHES. 95 The resemblances between ZLucernaria and Periphylla are for the most part anatomical in character, and so little is known of the development of both that there is little possibility of a comparison in this particular. The comparison, step by step, of the many likenesses between the two genera would take us too far into special studies of the peculiar anatomy of them both, but these points of likeness are of a most important character, and show that, notwithstanding one form is attached and. the other free, they may be closely allied to each other. The character of the development, and the different larval conditions which the Discophora pass through in that growth, present some of the most interesting facts in regard to these animals. In the progress of research into the anatomy and classifi- cation of the lower forms of animals three curious zodphytes, placed in three genera, had been described by different naturalists. These genera were called Scyphistoma or Scyphostoma, Strobila, and Ephyra. It was suspected that they were not adults, but in the early days of the history of marine zoology no one had any idea that these animals had close relationships with one another. The first and most important step in a true understanding of the nature of the larvee of the meduse was made by Michael Sars, by whom it was found that these three genera were one and the same, and Steenstrup, shortly after, recognized that there exists im the meduse a true alterna- tion of development such as the poet Chamisso had pointed out is found in the forms of the Ascidian genus Salpa, known as the “chain form,” and the solitary or asexual individual. Tn late summer and autumn specimens of Cyanea of large size are often taken in which the membranous fold which hangs downward from the oral region of the disk is loaded with white packets or bundles. These bundles are composed of ova, and if they are examined with a microscope of even low magnifying power will be found to have already entered upon the first steps in their development. In other words the genus Cyanea carries its young about and protects them in the folds of the mouth, from the very youngest to some of the higher larval conditions. The highest con- dition which it has in its career in the mouth-folds of the parent is what is known as a planula. The planula is an elongated, spheroidal body whose walls are formed of two or perhaps three layers, within which is a small cavity, and whose outer surface is covered with vibratile cilia. The function of the vibratile cilia is that of progression through the water, and, as a consequence, immediately on attaining this condition it swims away from the fostering care of the parent, and shifts for itself in the water. In this free-swimming or planula stage it remains until, freighted by the weight of increased age, it can no longer swim through the water by the ciliary movements. When that age comes in the progressive growth of the Cyanea, the embryo, which was formerly spheroidal in shape with symmetrical poles, becomes pear-shaped, presenting an obtuse and a pointed pole which can easily be distinguished. The larva next attaches itself by one of these poles to some fixed object, and the two following stages in its growth are passed through in that condition. Immediately after attachment there forms at the free end of the body a circle of little protuberances which, as the growth goes on, become more and more elongated, while in the centre of the circle, in the periphery of which they lie, an opening is found leading into a cavity in the interior of the body. The resemblance of the young animal, in this first of the attached forms, to the common fresh-water Hydra, which has been described, is very striking. The larva was one of those three supposed genera mentioned above which were formerly thought to be widely different from any of the 96 LOWER INVERTEBRATES. Discophora. It was then called Scyphistoma or Scyphostoma, and, notwithstanding we now recognize that it is part of the life history of the young of another genus, it is convenient to retain the name as char- acteristic of the first of the attached larvee of these animals. The Scyphistoma larva of Aurelia, for the following larva has not been observed in our Cyanea, although there is no doubt that its development is identical with that of Aurelia, is followed by one called the all Strobila, which like the former is still attached to some fixed object. In the growth of the Scyphistoma, that part of the free end of the larva situated inside the circle of tentacles, and in which the mouth lies, gradually rises higher and higher, forming an elongated cylinder of great relative size as compared with that of the original body of the Scyphistoma, which lies at its base, and upon which it is borne. There next forms on the outer wall of this cylinder a number of parallel constrictions which encircle the body of the cylinder in waving lines. These constrictions become deeper as the larva gets older, imparting to it a remote likeness, as Professor Agassiz has pointed out, to a “pile of saucers” resting below on the remnant of the Scyphistoma body and increasing gradually in size from the lowest member to the saucer which caps the pile. The next change in the progress of the development of dlurelia, after the Strobila just mentioned, is one in which the attached condition is abandoned and a free locomotor larva again adopted. This condition, for a reason identical with that mentioned with regard to the Scyphistoma, may be called the Ephyra, and more closely approaches that assumed by the adult than any of the others. The whole fixed Strobila, however, does not break’ from its attachment and swim away as an Ephyra, but fragments of the same, or individual saucers which compose the pile, in consecutive order one by one drop from their attachment and swim away as perfect little Ephyre. The cycle is now complete, and although the Ephyra differs greatly in form from the adult, yet still there are few important additions, and no departure from a direct growth in passing from one into the other. By reviewing the history which has just been considered it will be seen that in two of the intermediate larval conditions, known technically as the Scyphistoma and Strobila, between the egg and the parent, we have a wide departure from the adult in mode of life as well as external shape. We have seen also that the Scyphistoma does not pass directly as a whole into the Ephyra, but that it divides into fragments, each of which becomes a perfect adult. From one Strobila a number of Ephyre are produced without any conjugation of sexes in the attached animal. From this latter fact the mode of reproduction is said to be asexual and the Strobila an asexual individual. Gathering together the whole history of the development into one chain we find it presents this remarkable circumstance. Between the egg and the female Discophore from which it came there is an asexual, sessile larva which multiplies in an asexual way by simple division, thus producing from one egg a numerous progeny, each of which Fig. 89.— Sceyphistoma of Aurelia flavidula. FIG. 90.— Strobilia of Aurelia Slavidula. JELLY—-FISHES. 97 “has no known differences from the parents which produced the egg or spermatozoon. The principle is a wide-spread one in the animal kingdom, and is known as the alternation of generation. It is evident that the Scyphistoma and Strobila, more especially the latter, have a wide difference in shape from the form of the adult Cyanea. They develop directly from the egg and are asexual, while the adults which are developed from them are sexual, Sexual animals produce ova which de- velop into Strobile as before. Here then is an alternation of sexual with asexual forms of the same animal, and the technical name of the anomalous development is “ Alternation of Gen- erations,” nowhere better illustrated than in the Hydroidea and Discophora. The development of the ovum of Cyanea into the adult by a process of alternate generation, in which intermediate larvee are fixed to some foreign body and reproduce the adult by self-division, is not found in all the Discophora. As this method of growth may be said to be indirect in character, another, called the direct from the absence of these intermediate asexual conditions, also exists. In a direct development among the discophorous meduse we have simply a continuous growth from the egg to the adult. One egg produces only one adult. Such a development takes place in Pelagia’ and one or two related genera. Fie. 91.—Ephyra of Aurelia flavidula. Cuass IIT. —SIPHONOPHORA. Among the most beautiful of all the medusz is the group called the Siphonophora, the tube-like jelly-fishes. These animals are all marine and free swimming, and although they often have a hydroid-like shape, which resemblance becomes more marked when we study their anatomy, they are never attached to the ground as are the mem- bers of the Hydroidea. They are found in all oceans, although the tropics seem to be richest in the variety of these animals, and those from the Mediterranean have up to the present time been the most carefully studied and described. As their name signifies, the Siphonophora are characterized by a tube-like body, which is generally so much elongated that it takes the form of a small axis or stem. Although there are several genera in the group where the body does not assume a tubular form (of which one of the most common is Physalia), a tubular body seems as a rule characteristic of the group. The relationships of the Siphonophora to other meduse have been variously inter- preted by different authors. By the majority they are regarded as comparable to the Hydroidea, and are often called the free-swimming hydroids, in distinction from those already considered which are fixed. Others still compare them with the gonophores of the hydroids, some of which as the genus Lizzia bud off from the side of their manubrium new individuals, which later develop into medusz like their parent. The Siphonophora would be regarded by them as similar to the parent with many attached young. While many facts can be mentioned in support of either of these theories, it may be said that the differences which exist between a free medusa and an attached VoL. 1. —7 a 98 LOWER INVERTEBRATES. hydroid are not very great, and although at first sight it might seem as if the two* theories involve very different comparisons, they are in reality identical. OrvEr I. — PHYSOPHOR. One of the most interesting forms of Siphonophora is the genus Agalma, the name of which dates back to the days of Eschscholtz, the father of the study of actinology. It is the type of a family known as the AcaLmips#, and belongs to a larger group of Physophore or float-bearing Siphonophora. The genus Agalma when floating in the water, will be found to be made up of two kinds of bodies. The first of these are transparent, crystalline in appearance, and are easily detached from their connections with each other; the second are more opaque, flexible, and smaller, while they are more tenacious in their attachments to the animal. All are strung together on a common axis or stem which is very flexible in its character. The Agalma as it floats in the water is of a very fragile nature. So delicate is it in fact that it cannot be raised out of the water in the hand without the appendages being torn from their connections with each other. The only way to capture it entire is to place under it, as it moves about in the water, some receptacle which will hold liquid, allowing it to float in with the water. The water contained in the receptacle and the animal can then be raised together out of the SY sea. Even when the greatest care is shown in its Va capture it retains its appendages but a short time yj as when kept in confinement, and soon loses them fh fh all and shrinks to an insignificant size as UA compared with its former proportions. ) AS The axis or stem of the Agalma is a most characteristic structure. It extends from one extremity of the animal to the other, and affords an attachment to all the appendages which make up the whole. It is very flexible, colored a ¥ rosy pink, is hollow throughout, and about the diameter of a knit- ting-needle. At one end, which may be Fi. 92. — Agalma elegans ; a, float; b, nectocalices; c, covering scales; d, feeding polyps; e, tentacles and tentacular knobs; f, tasters; g, sexual bells. called the upper ex- tremity of the axis, the stem is enlarged into a small globular body which is called the air-bladder or float. This float contains a little sac filled with gas, and in some related genera JELLY-FISHES. 99 has for a function the support of the axis in the water. In Agaima, however, it is so small that its functional importance in this respect ig very slight. The axis of the Agaima is divided into two regions, one of which lies adjacent to the float, and is called the nectostem, and the other, more distant from the same, the polyp- stem. In larger specimens the length of the nectostem is about one-third that of the polypstem. The former bears a number of appendages of interesting char- acter called the nectocalices. These bodies are situated in two rows or series, and are glassy clear in their transparency. Their union with the stem is of a very fragile nature, and easily ruptured when the animal is raised out of the water. If we examine a single nectocalyx we shall find that it resembles closely a medusa bell (hydroid gonophore) in which the walls have a more or less polygonal shape. This form is the result of a flattening of two opposite sides of the nectocalyx in order that it may fit closely in the series of which it is a member. Each nectocalyx has a cavity within, which opens into the surrounding water through a circular orifice, partly closed by a thin, washer-shaped body called the veil. The apex of the nectocalyx is situated opposite the external opening, and marks the point of union of the bell and the necto- stem. On either side of the apex, embracing the nectostem, the bell walls are con- tinued into gelatinous horns which closely interlock with similar projections from nectocalices situated in the opposite series. The arrangement of the nectocalices on the nectostem is as follows: There are two rows or series of these bodies placed diametrically opposite each other on the axis. Each series is composed of a number of nectocalices placed one above the other, fitting closely together by the flat faces on the outside of these bodies. The gelatinous horns already mentioned interlock with corresponding bodies from the opposite series. By the close approximation of adjacent bells on their flat faces, and the interlocking of bells from opposite series, a certain rigidity is given to this portion of the animal, notwithstanding the delicate attachment to the stem. The disposition of the nectocalices causes all the bell openings in each series to point in the same direction, or almost at right angles to the length of the axis. The action of the nectocalices is as follows: They are, as their name implies, structures for a propulsion of the Agalma from place to place through the water. When water is taken into their bell cavities, by a violent contraction of the bell walls it is violently forced out through the opening into that cavity against the surrounding water in which the medusa is floating. The necessary result of this action is that the animal is forced through the water in an opposite direction from that in which the resistance takes place. By a nice adjustment of the different bells, acting in concert or independ- ently, almost any motion in any direction can be imparted to the Agalma. Just below the float on the nectostem there is a small cluster of minute buds in which can be found nectocalices of all sizes and in all conditions of growth. The attachment of the nectocalyx or swimming bell to the nectostem, not only serves to move the animal from place to place, but also renders it possible for the swimming bell to receive its nourishment. Although the nectocalyx resembles very closely a medusa, it is a medusa bell without a mouth or stomach. It is not capable of capturing nourishment for itself, but is dependant upon others for that purpose. The nectocalyx has a system of tubes on its inner bell walls which communicate with the cavity of the nectostem by means of a small vessel which lies in the peduncle by which it is attached. Through this system of tubes the nutritive fluid is supplied to the nectocalyx from a common receptacle, the cavity of the stem. In the largest 100 LOWER INVERTEBRATES. specimens of Agalma which I have studied, there were seventeen pairs of well-devel- oped nectocalices. The appendages to the polypstem are somewhat different in character from those of the nectostem, and are of several kinds, differing in character, size, and shape. The first and most prominent of these are known as the covering scales. They are trans- parent, gelatinous bodies, and are found throughout the whole length of the polyp- stem. Their shape is quadrangular or almost triangular, and they are united to the axis by one angle. The upper and lower faces are flat, and the whole appendage has a thin, leaf-like appearance. Through its walls from the point of attachment to the distal angle there runs a styaight unbranched tube which communicates freely with the cavity of the stem. The covering scales are easily detached, and are incapable of voluntary motion. Their function seems to be to shield the structures which lie be- neath them. Below the covering scales three kinds of bodies hang from the polypstem. They are known as the polypites or feeding stumachs, tasters, and sexual bells. The polyp- ites are the most conspicuous of these bodies. They have a flask-like shape, and are united to the polypstem by one extremity, while the free end has a terminal opening which is a mouth. The walls of the cavity of the polypite are crossed longitudinally by rows of cells which have been compared to a liver. In the cavities of the polypites the half-digested food can be seen through the walls. The nutritive fluids formed in these bodies are poured into the cavity of the axis, there to be distributed throughout the different appendages of the animal. When indigestible substances, as the hard parts of Crustacea, are taken into the stomach they are thrown off again through the mouth-opening. I have never seen the polypites more than seventeen in number, and they hang at regular intervals along the whole length of the polyp- stem. One of the most prominent bodies next to the nectocalices and covering-scales in the Agalma are the so-called tentacles, which hang from the base of the polypites, and which when extended are very long. The tentacles of Agalna are long, highly flexible, tubular filaments whose function is the capture of food. At times widely extended their length is little less than that of the Agalma axis itself. At other times they are drawn up under the covering-scales at the base of the polypite, and have a very diminutive size. Along their whole length they are dotted with crimson pendants of minute size which are called the tentacular knobs. These will be found, on close study, to be of a very complicated structure. Their true function is somewhat prob- lematical, but they are supposed to assist in the capture of the food. In addition to the well-developed tentacular knobs which dot the whole length of the tentacles, there are many half-grown bodies of the same character clinging to the base of the polypite. Alternating with the polypites at intervals along the polypstem are found very curious bodies called tasters, which have a close likeness to the flask-shaped feeding zooids. These bodies are without a mouth-opening at their free extremity, while from their base hangs a long, highly-contractile filament which is destitute of tentacular knobs. The tasters have an internal cavity which is in free communication with that of the axis of the animal. Various functions have been assigned to the tasters, but none without objections seems yet to have been hit upon. Their usual position is in clusters midway between the adjacent polypites. The term taster is somewhat mis- leading, for these bodies do not have gustatory functions. JELLY-FISHES. 101 The sexual bells are of two kinds, male and female, and both are found in grape- like clusters, the male near the base of the tasters and the female near the poly pites. If we isolate one of the members of a cluster, we find that it has a bell-like shape, and that the ova or spermatozoa are found on a proboscis within. Each bell hangs from the cluster by a tender peduncle which arises at its apex, and each female bell contains a single ovum. The growth of the young Agadma from the egg to the adult is of a rather compli- cated nature. When cast in the water the egg is a tiny, transparent sphere barely visible to the naked eye. After fecundation, and obscure changes similar to a seg- mentation of the yolk, a slight protuberance arises at one pole. This prominence is formed of two layers between which, in a short time, a third layer is also formed. The outer layer is the ectoderm, the middle the mesoderm, and the internal the endo- derm. Between the endoderm and the remainder of the egg there is a cavity called the primitive cavity. As the embryo grows older the elevation at one pole increases in size, and the proportion in thickness of the middle layer, as compared with the ectoderm and endoderm, becomes very large, while the ectoderm becomes very thin. The prominence has now assumed a helmet-like shape, and fits like a cap over the remnant of the yolk. The whole larva in this stage of growth is called the primitive larva or Lizzia-stage, and the cap-shaped covering, the primitive scale. The primitive scale is an embryonic organ which is lost in subsequent development of the larva. Immediately after the primitive larva stage there is found to develop under the primitive scale an air-bladder or float, which first appears as a little bud near the open- ing into the primitive cavity, which has now taken the form of a tube in the primitive scale lined with endoderm. At about the same time also there appears a covering- scale of very different form from either the cap-like primitive scale or the covering- scale of the adult Agalma, which have already been described. The float is the permanent float of the adult, while the second formed covering-scale, like that of the first, is also embryonic and larval in character. The larva has now the following parts: 1, The remnant of the yolk; 2, a cap-shaped covering-scale; 3, a second em- bryonic covering-scale, and 4, a float. As the larva grows older more covering- scales like the second appear, and the beginnings of a tentacle and tentacular knobs are seen at the adjacent end of the growing larva. At the same time the yolk becomes elongated, and in its walls appear reticulated masses of red or crimson pigment. The tentacle first formed as well as its pendants, the embryonic tentacular knobs, are transient in character. They differ essentially from the adult knobs, and are confined to this stage in the development of the larva. Meanwhile the primitive scale ‘is lost, and a circle of covering-scales of the second kind appears at the base of the float. This larva is called the Athorybia larva from its remote resemblance to a related adult genus called Achorybia. The appendages of this larva are: 1, a float; 2, a crown of embryonic covering-scales; 8, the remainder of the yolk-sac with an attached tentacle and temporary pendants. The next following larval condition of Agalma is one in which the embryonic covering-scales have disappeared and new scales like those of the adult have formed. Four well-developed nectocalices appear on a nectostem, and an adult polypite bearing the characteristic pendants of the adult has grown on the extremity of the short polyp- stem. A remnant of the yolk-sac, however, still persists, and from it depends an embry- 102 LOWER INVERTEBRATES. onic tentacle and its characteristic side branches. The Physophora larva resembles the adult in all particulars, except size, and the presence of the last of temporary organs later to disappear in the growth of the Agalma, viz., the embryonic tentacle. Several other genera of Physophores are so closely allied to Agalma that they are placed in the same family. One of the most interesting of these is the genus Agalmopsis, which differs from Agalma in its slighter form and the intimate structure of its ten- tacular knobs. alistemma has also a pecu- liar tentacular pendant which differs from those of Agalma or Agalmopsis. In the adult knob of Agalma the following struc- tures are found: 1, an involucrum; 2, 2 sac- culus; 8, terminal filaments and vesicle. The involucrum is a membranous sac which covers ! the knob when the other parts are retracted. The great mass of the knob is made up by the sacculus, which is corkscrew-shaped and dark crimson in color. At one extremity it is fastened to the inner walls of the involu- crum, the free end bearing two terminal fila- ments and a vesicle. The various genera of Agalmide differ in the character of this knob. -lyalmopsis has a sacculus and involucrum, but no vesicle, and only one terminal filament. J/u/istemma, probably the type of another family, has no involucrum, while it possesses a spirally- coiled sacculus and a single terminal filament. The genus Crystallodes has tentacular knobs like those of Agalma, and is by some authors made a species of this genus. It differs, how- ever, from Agadma in the rigid nature of the axis, in the shape of the covering-scales, and in minor points in the anatomy of the nectocalices. The genus Stephanomia, a name which has been applied to genera of Siphonophora of widely different form, was given by the elder Milne-Edwards to a Physophore in which there are many series of nectocalices appended to the nectestem. S. con- torta is one of the most beautiful and graceful of all the Siphono- phores as by the combined movement of its many swimming-bells it gaily swims along in the water. It is peculiar in this respect, that the polypites are mounted on a long peduncle, which also bears the covering-scales and the tentacles. The tentacular knobs resemble more closely those of Halistemma than of Agalma. It may be regarded as the type of the family Forsxkaniap a. One of the most beautiful genera of Puysornorm. is the Fic. 93. — Tentacular knob of Agalmopsis. ee 9 cs he” fy = aoe pana ee es ERAT > ied eS es ES Fic. 94. — Agalmopsis picta. interesting animal known as Physophora, called in the dialect of the Messina fishermen, “Boguetti.” Physophora is remarkable in possessing no polypstem, but in place of this JELLY-FISHES. 1038 structure the axis is enlarged into a bag-like inflation. There is, however, a well- developed nectostem and two series of nectocalices as in Agalma. Around the cir- cumference of the inflation, which takes the place of the polypstem, the tasters with their short, tentacular filaments are arranged side by side. The polypites and sexual Fig. 95.— Physophora hydrostatica. bodies are found below these structures. No true covering-scales exist in the genus Physophora. One of the largest of all the Physophore is the genus Apolemia, the type of the Aporemiap.®, which is called by the Italian fishermen by the suggestive name of “Jana di mare.” In this beautiful Siphonophore we have, as in other float-bearing meduse thus far considered, a double row or series of nectocalices, but unlike the last mentioned genera, there arises from the nectostem, small bodies resembling j 104 LOWER INVERTEBRATES. minute tasters which wave about in the water with great freedom. The polyp- stem also, instead of being covered throughout its whole length with covering- Fia. 96.— Portion of Apolemia. scales, has these structures arranged at intervals and in clusters, each with tasters, polypites, and sexual bodies. OrpER JJ. — PNEUMATOPHOR A. There are two genera of Siphonophora closely related to each other and to the group of Physophore already studied, which are now looked upon as forming a group by themselves. These genera include the well-known Portuguese Man-of-War or Physalia, often erroneously called by sailors the Nautilus, and a less common genus, Rhizophysa, one of the most bizarre forms of these animals. Physalia is one of the most common of all the Siphonophora in tropical oceans. The most conspicuous part of this animal, as it floats along on the surface of the water, is an enlarged air-bladder, six or eight inches in length. On the upper side of this float there is a raised crest colored by brilliant blues, yellows, and pinks. On the under side of the same there hang a great variety of appendages of several kinds. There are feeding-mouths or polypites, flask-shaped bodies resembling tasters with long tentacles, which, as the animal floats in the water, extend far behind it in the water as magnificent streamers, and grape-like clusters of sexual bodies. The Physalia is wholly destitute of a tube-like axis, and as it floats on the surface of the water, resembles more a bladder with richly variegated walls, than the tube-like forms which we have already considered. The closest relative to Physalia, as far as anatomy goes, to which affinity also what is known of their development adds additional evidence, is the strange genus Rhizo- physa. Rhizophysa is a simple skeleton of a siphonophore. It is the axis of an JELLY-FISHES. 105 Agaima stripped of all its appendages, except feeding polyps and sexual bodies. There is in it no distinction between nectostem and polypstem, and no means of voluntary motion. The float is particularly large owe Tan and has an apical opening through as "ela o, which its contents communicate with 42 the surrounding water. The feeding polyps hang from the stem at regular intervals when extended, and midway between them appear on the same axis botryoidal clusters which are called the sexual organs. Tentacles hang from the bases of the polypites as in other related siphonophores. The tentacular knobs have, however, a highly charac- teristic form which varies with different species in number and general anatomy. OrpDeErR III.— DIPHY 4A. In all the genera thus far studied, there is always a float at one extremity of an axis when such was present. In if . no case isa float missing, although often- yf mt times it is functionally unimportant. a ip In none of the remaining Siphonophora, 5 | § Sly P on the other hand, is a float present. eo / These last medusee may conveniently Be : be divided into the Diphyz, in which FiG. 97. —Physalia arethusa, Por- a tuguese Jpan-of-war, one-fifth there are one or two nectocalices, and : the Hippopodie, floatless forms in which there are several or more than two swimming-bells. One of the best marked families of the Diphye is the Drrny- 1p#, of which Diphyes is a typical genus. This genus and most of its relatives is smaller than the majority of those already studied, and are easily distinguished from the former by the absence of a float, and the presence of but two nectocalices. The two swim- ming-bells which are possessed by Diphyes are of somewhat differ- ent form. The anterior is conical in shape in order to facilitate rapid progression through the water, while the posterior which lies behind it, seems to perform the greater part of the work in the progression of the medusa. As in Agalma, onward motion > Fic, 98. — Rhizophysa. is caused by the resistance of the water as it leaves the bells on the surrounding medium in which the animal swims. The motions of the nectocalices are spasmodic and not long continued as in the Agalma and other Physophore. The axis of Diphyes hanging from the interval between the two bells, is a long, filamentous, flexible structure not. unlike that of Agalma. It is highly contractile, and has a cavity throughout its entire length. The polypites arise at intervals along the length of the stem, and are in no respect peculiar. Each polypite bears a tentacle and tentacular 1 106 knobs, or pendant side-branches. LOWER INVERTEBRATES. At the point of attachment of the polypite to the axis, we also find a transparent bell-shaped covering-scale and a cluster of sexual bells A ; "Bf th fA 4 { 7 ah fi ) Fic. 99. — Diphyes. with eggs and spermatozoa. Each cluster of bodies near a polypite ultimately sepa- rates from its attachment to the Diphyes axis, lives in- dependently, and is called a diphyizoéid. There are several families related to the Diphyide which might be mentioned. They differ from it in the character, size, and general anatomy of the two necto- calices. One of the most marked of these is Praya, a solitary genus composing a family called the Prayip.r. In Praya there are two nectocalices which are of ~ about equal size, and have a rounded or semi-ovate form. The bell walls are not as rigid as those of Diphyes, and their motion less spas- modic. The axis is very long and flexible, and the polypites, found at intervals along its length, are pro- tected by a helmet-shaped covering - scale, beneath which are found clusters of sexual bells mounted on short peduncles. The genus is one of the most striking of the many beau- tiful genera which charac- terize the Siphonophore fauna of the Mediterranean Sea. Ihave also observed a fragment of a large Praya near Fort Jefferson, Tortugas, Florida. The fourth of the large groups into which the true Siphonophora may be divided is called the Hippopoprz from a genus sometimes called Hippopodius, which has a highly characteristic and peculiar structure. Fig. 100. — Praya, Gleba (Hippopodius) is in most respects related to the Diphye, but unlike them has more than two nectocalices. There is no float and no extended axis with individuals found at intervals in its length. No polyp- JELLY-FISHES. 107 stem is developed, and the nectostem has little in common with that of Agalma. The nectocalices are of characteristic shape and different from those of any- other siphono- phore. Each bell has the shape of a horse’s hoof, and has a very shallow cavity and rigid walls. As far as yet known the Hippopodie have no diphyi- zoéids such as exist in several genera of the Diphye. Orper IV. — DISCOIDEZ. Among the many interesting forms of Meduse related to, and by most naturalists included in the Siphonophora, are two beautiful genera called Velella and Porpita. These, with a genus Lataria, which is probably the young of one or the other, make up a group called the Discoidee. Velella has borne the name which designates its most striking peculiarity since the middle of the fifteenth century, on account, perhaps, of a somewhat fanciful likeness to a little sail. It is commonly called in Florida, where it is sometimes very abundant, the “ float,” and is likewise commonly confounded with the Physalia or Portuguese man-of-war. The body or disk of Velella has an oblong shape, flattened upon its Fig. 101.— Diphyizooid of Praya. Fic. 102. —Velella limbosa. upper and lower sides. The float is composed of a number of concentric compart- ments in free communication with each other, seven of which open externally in a line extending diametrically across the disk. In the whole diameter there are fourteen such openings, seven in each radius. A triangular sail rises on the upper side of the Velella disk and extends diagonally across its surface. It is firmly joined to the upper plate of the float. Over the trian- gular sail as well as the float, there is stretched a thin, blue-colored membrane, which is continued into a variegated soft rim along its border and around the rim of the float. In our most common American Velella, which often reaches a length of four or five inches, the portion of the rim of this membrane around the disk is entire; in some species, however, it is continued into elongated appendages. The most important appendages are found on the under side of the Velella disk 108 LOWER INVERTEBRATES. which is commonly submerged as the animal floats on the surface of the water. Of these perhaps the most prominent is a centrally placed body which hangs downward below the remaining appendages, and is open at its unattached extremity. This structure is the feeding-mouth or polypite, and is single in both Velella and Porpita. In the zone just surrounding the polypite we find a large number of small appendages, each of which has a thread-like shape bearing along its sides a number of little trans- parent buds in all conditions of growth. Each of these little bodies ultimately sepa- rates from its attachment, and in the form of a minute jelly-fish, not larger than a pin- head, swims about endowed with independent powers of life for a considerable length of time. The medusa which has thus separated is known as a Chrysomitra. Surround- ing the bodies last mentioned on the lower surface of Veledla, there is a circle of feelers of bluish color which are commonly in constant motion. One of the most prominent superficial differences between Porpitu and Velella is the total absence of a triangular sail in the former genus. They are commonly found associated together, and often accompanied by a third jelly-fish allied to both, called Rataria. Crass ITV.— CTHENOPHORA. The highest of the jelly-fishes, both on embryological and anatomical grounds, are known as the Ctenophora. In these animals that characteristic of higher forms of life known as bilateral symmetry appears for the first time. An obscure symmetry which has been called by some naturalists bilateral, appears among the Siphonophora, and even in the Hydroidea. In the Ctenophora, however, it is more plainly indicated than in either of these groups. One of the earliest mentions which we have of the ctenophorous meduse we owe to Martens. Freiderich Martens was a ship’s physician or a ship’s barber, as he styles himself, who accompanied Captain Scoresby in a voyage of exploration into the Polar Seas. He first found one of these beautiful meduse in the neighborhood of the island of Spitzbergen. Eschscholtz was the first to recognize the common likenesses between the different members of the group, and gave to them the name of Ctenophora or comb-bearing meduse. The Ctenophora take their name, as he first pointed out, from the existence on the external body walls of eight rows of vibratile plates called combs. These combs are arranged in such a way that in flapping they strike upon the water, and by their mo- tion the jelly-fish is driven along through the water. We find here for the first time since our studies of the Celenterata began, a large group of animals where movement . in the water is produced both by special locomotive organs and contractions of the body. The varieties in form in the bodies of different Ctenophora is very great. In some genera they appear as long ribbon or belt-like creatures which move through the water with serpentine movements, in others as transparent caps or globular gelatinous masses over which the rows of combs shine with most lovely iridescent colors. No greater variety of more beautiful genera is to be found anywhere among the meduse. Cestus, called also the Venus Girdle, is perhaps the most striking genus of the Ctenophora. Its shape departs the most widely of all the Ctenophora from that of the medusoid types. In Cestws the body of the jelly-fish has a girdle or belt-like form, and is moved more by the contractions of the body thar by the rows of combs which fringe its edges. The animal is very transparent and extremely tender, so that it is with the JELLY-FISHES. 109 greatest difficulty taken from the water without breaking. Its motion through the water is a graceful undulation to which body contractions and vibrations of the combs contribute. The mouth of Céestus is situated midway in its length between the two extremities of the belt-like body. On either side of it there hangs a single short tentacle which protrudes from a tentacular sac. Opposite the mouth there is a sense-body, or otocyst as it is commonly called, in which is situated a compound otolith. The rows of combs upon the external surface of the body of Cestws are not as conspicuous as in some other genera, but the course of their lines can be easily traced. The enormous expan- sion of the two lateral lobes of the body which give a girdle-like form, impart to the rows of combs which lie in these regions an extraordinary development as compared with Fic. 103. — Cestus veneris, Venus girdle. those which lie in the intermediate regions or on the flattened sides of the body. The adult Cestus reaches a length of from two to three feet, and is one of the largest as well as most beautiful ctenophores of the Mediterranean. There is scarcely any color in its body walls. Of the many genera of meduse closely or remotely allied to Cestus, one of the most interesting and least known is a genus called Ocyroé from the Gulf of Mexico and the Caribbean Sea. This genus, like many other ctenophores, and especially like Cestus, is very transparent, and has on the external body-surface, eight rows of vibra- tile combs, the lines of which converge at a point near that pole of the animal in which a sense-organ is situated. One of the most extraordinary things about Ocyroé is the great development of two opposite sides of the body into wings. In Cestus the oppo- site sides of the body are so developed that a band or belt-like form is given to the 110 LOWER INVERTEBRATES. animal, but in Ocy7oé these lateral developments take on the form of wings or similar bodies. Cestws moves through the water by a slight undulation of the body, while Ocyroé does the same by a flapping movement of its greatly developed lateral lobes, and by their beating upon the surrounding water. When Ocyroé is at rest, the lateral wings are widely extended, giving to the animal a remote likeness to Cestus. When, however, motion is attempted, the lobes are raised above the horizontally extended position which they occupy at rest, and then violently swung downward, passing through almost 180°. This flapping of the two wings in concert is continued several times, and in that way the animal is propelled through the water. The function of the rows of combs in the movements of the medusa is secondary to the flapping move- ments of the lateral wings. The body of Ocyroé, from two sides of which the wings arise, is of oblong, oval shape, with a mouth at one pole, and a cluster of otoliths in an otocyst at the opposite. There is no vestige of tentacular appendages near the mouth, and the lips are undi- FiG, 104. — Ocyroé crystallina. vided, smooth, and highly flexible. Ocyroé thus far has been taken only from the waters of tropical America. In colder latitudes as on ‘our New England coast, we have a beautiful ctenophore called Bolina, and another very closely allied genus known as Miemiopsis. These meduse are in many respects most closely allied to Ocyroé, or rather Ocyroé seems an aberrant form of these more northern jelly-fishes. Although the same lateral lobes exist in both genera, their importance in Bolina, as far as movement is concerned, is much less thaw in Ocyroé. They are also seldom or never carried extended horizon- tally at right angles to the body, as in the curious genus Ocyroé. Bolina is one of the most transparent of the comb-bearing meduse. The body is very gelatinous and highly phosphorescent. The sides of the body are developed into two larger lappets or lobes which are carried or hang vertically instead of horizontally. On account of the contractile powers of the body walls, Bolina can vary its outlines very considerably ; as a rule, however, when the body is seen from the side, it has an oval or elongated form. Eight rows of vibratile combs contribute to the propulsion of the medusa through the water. ‘These lie upon the external surface of the body, and arising from the pole opposite the mouth-opening, extend to the more distal edge of the lateral expansions to the vicinity of the mouth. From the great development of the lateral lobes, the four lines of vibratile combs which ‘cross these bodies are much longer than those “which lic on the body regions between them. Two tentacles are found hanging from the sides of the body of Bolina. These tentacles are of diminutive size in the adult, and are remnants of structures which in early conditions of growth were very much more developed. Pleurobrachia and Bougainvillea. JELLY-FISHES. 111 Four other curious appendages called auricles are found on the sides of the body in the grooves which lie on opposite ends of a horizontal diameter of the body, and which are enclosed by the edges of the lateral lobes. These auricles are simply exten- sions of the body walls on the sides of the mouth, and their edges are skirted by vibra- tile plates somewhat like those found on the exterior of the body in the lines mentioned above. : The stomach and chyme tubes, vessels analogous to veins and arteries, in Bolina do not differ greatly from the same structures in other Ctenophora, but are highly characteristic as compared with similar bodies in other meduse. ~The mouth of Bolina is a narrow, elongated slit, opening with a correspondingly flattened receptacle called astomach. From the end of this stomach opposite the mouth, there arises a number of vessels which pass to various regions of the body: One of the most important of these is continued directly to the aboral pole of the medusa, and is known as the fun- nel. Of the others, four, after a bifurcation, pass to the vicinity of the rows of combs, and following a meridional course, eventually join each other in pairs near the oppo- site pole of the jelly-fish from the sense-body or in the lateral lobes. There are two tubes which originate from the base of the funnel and extend along the sides of the body to the tentacles which from their characteristic course have always attracted attention. Their function seems to be to convey the nourishing fluid to the tentacles into which they eventually open. There are several genera of ctenophorous meduse allied to Bolina. One of the most pompous of these, as well as the largest of the comb-bearing jelly-fishes, with enlarged lateral lappets is a genus called Chigja. This genus is remarkable in many particulars, but more especially in the great length of the auricles which appear as long, filament-like tentacles, and the very complicated course of their chymiferous tubes. Many classifications have been made of the Ctenophora, but as yet all are open to objections of some kind. One of the last suggestions with this subject in view emphasizes the presence or absence of the tentacles. By this classification we would have the Ctenophora divided into the Tentaculata and the Nuda, accordingly as tentacles exist or are wanting. In the genera which we have already considered, with the exception of Ocyroé, well-developed tentacles are found either in the larval or adult condition. Probably the best example, however, which might be men- tioned of a tentaculated ctenophore is the genus Cydippe or Pleurobrachia. There are often in our New England bays and harbors, after a southeasterly wind, a number — myriads at times — of little transparent gyrating spheres, not larger than a com- mon marble. These little gelatinous spheres move through the water with a great variety of motion, and seldom change in any Fic. 105, — Pleurobrachia important particulars the regular spherical form of their bodies portion, ce en. in the manner characteristic of the genera of Ctenophora to aes Ce which we have referred. When the cause of this variety in motion is sought out, it will be found that on the surface of the body there are a num- ber of iridescent lines extending from one pole to another, and that each of these lines is formed of a number of minute comb-like bodies such as exist in other Ctenophora. 112 LOWER INVERTEBRATES. It is by the strokes of these bodies on the surrounding water that the jelly-fish is moved about from place to place. The tentacles of Pleurobrachia, oftentimes almost wholly inconspicuous they are so securely packed in little lateral pockets on either hemisphere of the medusa, are most important structures in the economies of this beautiful medusa. It often happens, when the jelly-fish is at rest, that the tentacles are extended from their pockets, stretching far outside of this receptacle. Their length when extended in this way is so great that it seems impossible that they can be retracted into the tentacular pockets. The tentacles are two in number, each tentacle bearing a large number of side branches of brownish color, and in the movements of the medusa are often thrown into the most fantastic shapes. The Ctenophora Nuda, or those ctenophores which are destitute of tentacles, are represented by a very beautiful medusa called Beroé. This is perhaps one of the most remarkable jelly-fish which we have yet considered, although it is without doubt one of the lowest in its organization. The form of the body of this animal is that of a cap or rounded sac of very simple structure. If we closely consider the structure of this animal it will be noticed that, extending longitudinally across the outside surface of the body, there are eight rows of combs as in the other Ctenophora. At the pole of the body there is a sense-body in a similar position to that of the sense-body of other genera. The whole interior of the body serves as a stomach, and into it there opens a mouth of very great size. The stomach will often be found gorged with food, and the animal swollen to double its natural size by the mass of food collected in this organ. This animal is indeed one of the most ravenous genera of meduse. There are no tentacles in the genus Beroé and no sign of tentacular sacs. The chymiferous tubes have a very simple course in the walls of the body, extending from common origin to the vicinity of the mouth in an almost direct course with, however, many side branches. The color of our common Beroé is a delicate pink. Crass IT. — ACTINOZOA. Much discussion, happily now for the most part of the past, hangs about our knowl edge of the nature of the Actinozoa or corals. Their relationship to animals was first recognized by Peysonelle, who records his observations in the quaint language of a former century. The word Actinozoa, of comparatively modern date, has an almost exact equivalent in the older term Zodéphyte, and refers to a great variety of animals fixed to the ground like plants, and possessing in common with them certain superficial resemblances. ‘They all have remote likenesses to a plant or flower, with which for a long time in the history of science they were confounded. It includes the great families of reef-building corals, and has an added interest on account of the many questions which suggest themselves in relation to the method of formation of coral reefs and coral islands. In the general structure of their bodies the Actinozoa differ somewhat from the Hydrozoa, but the difference is not of such great importance as to call for a wide separation in a scheme of classification of the two. The differences would appear at first sight very great. Nothing for instance could seem more different than the soft, gelatinous body of the medusa and the stony mass of a coral, and yet this difference has no homological meaning, and as far as general structure is concerned the two are identical. In the medusz the body is so filmy and transparent that it is often wholly invisible as the CORALS. 113 animal swims in the water, and the sense of touch is necessary to supplement that of sight in order to know where the animal is. In stony corals on the other hand we find secreted in the animal tissues a very hard, cal- careous substance which forms a skeleton, and, when the secretions of a number of individuals are united, an axis or head upon which the corals build or secrete their skeletons. When we view a white branch of coral we see nothing of the animal save its dried and bleached skeleton, from which most of the organic nature has dis- appeared. If we could go to the tropics and study the meduse and corals alive many points of likeness might be traced in their general structure. We are accustomed to associate with all animals a certain amount of motion from place to place in the medium in which they live. In the Actinozoa, however, we find very few of the adults endowed with locomotive powers, and all, as a general thing, are fixed to some foreign body. The solid carbonate of lime which the majority of the corals secrete in their tissues is, in respect to its method of formation, identical with all secretions in animal bodies. It is not the work of the coral any more than the shell of the clam or the covering of the lobster is the work of the animals which they enclose and protect. It is an internal or external formation by secretion, and as a consequence coral animals are not mechanical builders any more than any other animal can be called the mechanical con- structor of its shell or skeleton. Many of the Actinozoa have no power of secreting hard matter in the form of a skeleton, and the bodies of such have a soft, gelatinous character, while in their tissues, as in those of the medusz, a large proportion of water is found. The solid secretions of coral animals, commonly known as coral, is sometimes erroneously supposed to harden on exposure to the air. This opinion is probably well founded as far as coral rock, a chemical product of the cementation of coral sand in a way to be explained, is concerned, but is wrong as regards the coral in the form secreted by the animal. Although it appears to harden by the loss of animal matter, the skeleton itself changes but very slightly, if at all, in its hardness after the death of the animal from which it came. The genus Actinia, a soft-bodied Actinozoan which has not the power of secreting carbonate of lime, is for various reasons the one commonly taken to illustrate the anatomy and characteristics of the group. -Actinia, found in almost all seas in the temperate as well as torrid zones, is represented by a large number of species, the ma- jority of which are of comparatively large size. The Sea-Anemone, Metridium VOL. 1.—8 Fig. 106. — Monoxenia, young haleyonoid polyp. 114 LOWER INVERTEBRATES. marginatum, our New England Actinia, has been chosen to illustrate certain of the important general features in the anatomy of the group. . Metridium is common almost everywhere on the New England coast in sheltered. pools left by the tides, on spiles of bridges, and on rocks near low-water mark. Under the name of sea-anemone it is known to collectors of marine curiosities as the common zodphyte from Eastport to New York. In no place have I seen the species larger than on the spiles of Beverly Bridge and at Nahant, but equally giant specimens have probably been taken from other localities. The diameter of the largest Metridium ‘found in the former locality measured, when expanded with water in its tissues, a little over ten inches in diameter. Forms of Actinaria allied to Metridiwm from the Florida Keys and Bermuda attain a gigantic size, often fifteen to eighteen inches in diameter. When the Actinia is seen from one side it will be found to have a cylindrical body firmly fixed at one end to some foreign object, and bearing at its free end a circle of tentacles surrounding a central mouth. The tentacles are thickly set together, are very movable, and when the animal is alarmed are quickly drawn to the body. The whole body and the tentacles are very much inflated with water, which at the will of the animal can be expelled from the body through the mouth, the body walls, and the tips of the tentacles, where there are small orifices. When inflated with water the body and its appendages are all expanded, but when this water is expelled the animal shrinks to a shapeless lump, the tentacles are drawn back, and there is little resem- blance to its former condition. The internal structure of Metridium is of a character typical for most of the Acti- nozoa. If we make a horizontal section through the body about one-half the distance between its attached and free extremities the cross-section thus made will present the following characters. In the centre lies a cavity, the stomach, whose wall is held in position by radiating partitions passing from it to the outer walls of the body. Intermediate between these partitions there are radiating walls or septa which arise from the outer body walls but do not extend to those of the stomach. The body walls from which these partitions all arise are, as a general thing, thicker than those forming the partitions, and in their sides there are openings through which the water at times leaves the body cavity. The method by which the Metridium feeds is very simple. The food captured by the tentacles when the anemone is expanded is passed from one member to another through the mouth into the stomach. Here digestion takes place, and after the soft. portions have been digested the harder parts, skeletons, shells, and the like, are thrown off again through the mouth by which they entered the stomach. The fluid passes from the stomach through an opening opposite the mouth into the body cavity, bath- ing the interior of all the organs which lie in that place. Special organs of respiration are not unknown among genera of Actinaria allied to Metridium, but in this genus probably the whole external and internal surfaces of the body contribute their part in the performance of this function. In Metridium special organs of sensation are of a very low grade of organization and of the simplest kind, as would naturally be expected from the attached life of the animal. Reproduction among the Actinozoa presents some of the most interesting features connected with these animals, and in the case of the coral colonies in which the reef- builders live, is the most important factor in the determination of the ultimate form. Three kinds of reproduction, which are known as generation by fission, by gem- mation, and by the laying of eggs, or ovarian, occur in the Actinozoa. The first two iy} fy Hy My) Ui Hy Zr a Ti ti) A uy x oN A GROUP OF EUROPEAN SEA-ANEMONES. 1. Thelia crassicornis, thick-petalled sea-rose. 2. Sagartia parasitica. 3. Actinoloba dianthus, sea-pink. 4, Sagartia viduata, “the widow.” 5. Sagartia rosea, red anemone. 6. Bunodes gemmacea, warty anemone. j. Anthea cereus, green anemone. CORALS. 115 methods are asexual in their character, the last sexual. In reproduction by a fission we find a simple voluntary self-division of a single individual into two or more second- ary animals. In many reef-building corals this method of increase is most natural in order to increase the size and style of growth of a colony of these animals, Among the solitary forms like Metridiwm it is seldom found. A second mode of increase, a reproduction by gemmation or budding, is much more common than that of fission and is found in the solitary as well as the communal forms of Actinozoa. In the formation of a bud we have a very simple method of reproduction. In such a case there simply appears on one side of the base of the body, or, as in some genera, on the disk surrounding the mouth, a small protuberance, which is a simple elevation of the body walls. From this simple beginning of a bud we pass to a more developed condition in which the protuberance has become a small coral animal attached to the Fic. 107.— Crambactis arabica, sea anemone. parent at one extremity which is its base, and with a free extremity furnished with a mouth surrounded by a circle of tentacles in most respects identical with those of the mother. The bud from the parent has every resemblance to the parent, and can live independently although still attached, and drawing nourishment in part from her through the base of attachment. All the Actinozoa reproduce by means of eggs. The ova pass through the condition of a ciliated planula which is free-swimming and sometimes parasitic in its youth. Phenomena similar to those of alternation of generations have been found in some genera, but as a rule the development is direct from the egg to the adult. Special features in the development of individual genera will be touched upon as we continue our account of these animals. The Actinozoa are commonly divided into two great groups, easily distinguished from each other, and known as.the Actinoida or Zoantharia, and Halcyonoida or Alcy- onaria, which includes, roughly speaking, the reef-builders in the first instance and 116 LOWER INVERTEBRATES. the ‘“sea-fans,” “sea-pens,” and their allies in the second. Anatomically, the two groups are distinguished, in part, as follows: In the Actinoid corals we find a large number of internal radial septa and numerous external tentacula about the mouth. When the number of these organs is small they are generally in multiples of six, and in most instances there are no lateral appendages to the tentacles. When hard matter is secreted in the tissues it is commonly in the form of carbonate of lime. The second great group of Actinozoa, called the Halcyonoida, differs from the former in the possession of eight, or amultiple of eight, tentacles and body septa, while the former almost universally bear side branches and appendages. In those genera where a skeleton exists it is tough and elastic, oftentimes of very great hardness, as in the genus Jsis and the well-known ornamental coral of commerce. OrpvER I.— ZOANTHARIA. The so-called Actinaria, which are referred to the Actinoid corals, include a large number of interesting genera. As a general thing, these genera are solitary in their mode of life, and often reach a great size. One of the best known genera of the Actinaria is the genus Metridiwm, of which we have already spoken. Many of the Actinaria are either free-swimming in their adult form, are parasitic, or live with their bodies par- tially hidden in the sand; still others are attached to the ground. They do not, as a rule, secrete a calcareous or horny skeleton, and their bodies are usually very soft, without even the needle-like spicules which occur in the’soft forms of the Haleyonoida. One of the most interesting of the Actinaria is the genus EAdwardsia, which is not attached to the ground, but lives in the sand in its adult form, while in younger conditions it is free- swimming, even after the tentacles have reached a considerable size. The young Edwardsia was at first mis- taken for the adult condition of an Actinoid coral, and was described under the name of