CORNELL UNIVERSITY LIBRARY GIFT OF Dept. of Zaclogy Practical zoology for medical & junior PRACTICAL ZOOLOGY PRACTICAL ZOOLOGY MEDICAL & JUNIOR STUDENTS By f. D. F. GILCHRIST, M.A., D.Sc., Pu.D. Professor of Zoology in the University of Cape Town AND C. von BONDE, M.A. Lecturer in Zoology in the University of Cape Town NEW YORK WILLIAM WOOD & CO., 51 Firra Avenuz EDINBURGH E. & S. LIVINGSTONE, 16 anp 17 Tevior Pace 1922 PRINTED IN GREAT BRITAIN BY THE RIVERSIDE PRESS LIMITED EDINBURGH * PREFACE Tuts book is:intended for Students of Elementary Zoology. The part dealing with the Frog and the Platana or Clawed Toad has been in use for some time at Cape Town University, and has proved so valuable an aid to the work in the practical classes that other types have now been added in this new and enlarged edition. Being specially adapted for the requirements of students in South Africa, the book contains descriptions of certain South African types which are not dealt, with in other practical manuals; and, at the suggestion of the publishers, in order to make the work useful for other students, the principal European types, which are sometimes used in South Africa, have also been described. It is recommended that the Frog be studied first, as it is particularly suitable for an introduction to the subject. The other types may be taken in any order convenient. The instructions given throughout the text will be clearly understood by reference to the numerous figures. The figures are not to be copied by the .student.. A drawing of the actual dissection is to be made on the blank page provided ; and the student should be prepared to point out the various parts to the teacher. The instructions can be followed without preliminary lectures, and are designed for the use of medical students and others whose course in General Zoology may be unduly restricted by the inclusion of anatomical details. A short lecture course is often overburdened with these details which, we think, can much better be given in the form of a practical handbook. With a few exceptions, the figures are original and have been drawn from actual dissections. The publishers are particularly desirous of expressing their thanks to Mr Robert A. Staig (formerly Demonstrator of Zoology, School of Medicine of the Royal Colleges, Edinburgh, and University of Glasgow) for the con- tinual assistance of his advice in the preparation of this publication for the Press, and for the excellence of his work in reading the proofs and compiling the index. J.D. F. G. C. v. B. ZOOLOGICAL LABORATORY, UNIVERSITY OF CAPE TOWN, 15th May, 1922. CONTENTS PAGE VTHE Proteus ANIMALCULE (Ama@ba) a @ ; ‘ ‘ 2 VPue SLIPPER ANIMALCULE (Paramecium) : ‘ ; ; , 6 Monocystis ‘ . ; " ; ; ‘ . To /Seonces (Porifera) ’ : ; } : : : ; I4 VTHE FRESH-WaTER Potyp (Hydra) 2 5 ‘ ‘ j 20 . OTHE Ses-ANEMONE (Actinia) ‘ ‘ : ; ; . ‘ 34 /TuE Liver-FLUKE (Fasciola or Distoma) 5 a ; 40 vy THe Tapz-Worm (Taenia) : ; : : : : ‘ 46 VTHE Eartu-Worm (Luméricus) . : ‘ ‘ 54 THE MepicinaL LeEcH (firudo) ; ‘ ‘ ‘ 64 THE CockroacH (Leriplaneta) . : i 3 : ‘ ‘ 94 THE FRESH-WATER CRAYFISH (Astacus) AND THE Care CRawrisH ( Jasus) . 88 THE SnaiL (Helix) : ‘ d : ; ‘ , . II4 THE FRESH-WaTER MussEL (Anodonta) AND THE COMMON MARINE MUSSEL (Mytilus). ‘ : ; ; ; ; : . 126 THE LaNcELET (Amphioxus, syn. Branchiostoma) ‘ 7 4 E42 THe Spiny Docrisu (Acanthias, syn. Squalus), OR THE SPOTTED DocFisH (Scyllium), AND THE SKATE (Raia) ‘ 3 ; 5 . 152 Tue Froc (Rama) aND THE PLaTANA OR CLAWED Toap (Xenopus) . 188 Tue Pickon (Columba) . 5 ‘ 3 : q ‘236 THE Rappit (Lepus) : ‘ j ; i . . 266 A CLASSIFICATION OF THE ABOVE TYPES ‘ ’ . 316 INDEX : ‘ : ‘ 5 ‘ : ‘ ‘ 319 “8 vil = oor aA nr wprs PD PK KM BW eB eR RP Pe YE eS KH Soman anr wns eo 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. ' 33. 34. 35. 36. 37. 38. 39. 40. ILLUSTRATIONS PAGE Ameba proteus (highly magnified) : : ; ; . : 2 Paramecium caudatum (highly magnified) : i ; : 6 Life-history Stages of Monocystis agilis (highly nepaliads ‘ ‘ . 10 Transverse Section through a part of the wall of Sycon gelatinosum : . +414 Types of Sponge Spicules j : ; j . 18 Transverse Section of an Ascon Sponge Cuan é : . 20 Transverse Section of a Sycon Sponge . - j : j . 22 Transverse Section of a part of the wall of a Leucon Sponge . ‘ . 22 . Transverse Section of a Rhagon Sponge . ‘ 2 : P . 24 Hydra viridis. Longitudinal Section of Hydra. é . ‘ . 26 . Transverse Section of Hydra viridis, etc. . : e : : . 380 . Transverse Section of a Sea-anemone . : . , . 34 . Longitudinal Section of a Sea-anemone . , , : . 38 . Dorsal and Ventral View of the Liver-fluke (Pasciola) ; : : . 42 . Transverse Section through the body of a Liver-fluke . : ‘ . 44 .. The Beef Tape-worm (Taenia saginata) . F : ; z . 46 . A Mature Proglottis of Taenia solium . : : ; : . 48 . Transverse Section through a proglottis of Taenia solium : ; . 50 Earth-worm (Lumbricus terrestris) . 5 . : . . 54 . Alimentary, Vascular, Nervous and Reproductive Systems of the Earth-worm . 58 . Transverse Section eae) ae the middle of the body of the Earth- worm (Lumbricus) : : : » 62 The Leech (Hirudo medicinalis) . 68 Transverse Section ae a through the stiatig of the boay of tie Lash (Hirudo) . ; - 70 The Cockroach (padtanea Lpaseaien, “Male : : A . 76. The Cockroach... Front, side and dorsal views of the head 3 . . 78 Appendages of the Cockroach (Periplaneta) . ; . @ . 80 Alimentary and Nervous System of the Cockroach . ‘ : . 84 The European Fresh-water Crayfish (Astacus) . 7 ; . - 90 The Cape Crawfish or Kreeft (Jasus lalandit) . . : ; - 92 Appendages of the Fresh-water Crayfish (Astacus) ‘ : ‘ . 96 Appendages of the Cape Crawfish (Jasus) i . 100 The Fresh-water Crayfish (Astacus). General Structure ad Nersous Sontein - 108 The Cape Crawfish (Jasus), General Structure and Nervous System ‘ . 110 Phyllosoma larva of the Crawfish . . ; : ; ; . 112 The Snail (Helix aspersa) 3 : ‘ : . 114 The Snail (Helix). Dorsal view after anand of shell . : 4 . 116 Dissection of the Snail (Helix) . ‘ . : ; . 118 The Nervous System of the Snail (H eli) i . 122 Inner view of the left half of the head region icronteuuons ete. ) et the Snail . 124 The Fresh-water Mussel (Anodonta cygnea) . . . . - 126 ix FIa@, 4l, 42, 43. 44. 45. 46. 47, 48. 49. 50. 51. 52, 53. BA. 55. 56. 57. 58. 59. 60. 61. 62. 63. 64. 65. 66. 67. 68. 69. 70. 71. 72. 73. 74, 75. 76. 77. 78. 79, 80. 81. 82. 83. 84, 85. ILLUSTRATIONS The Common Marine Mussel (Mytilus edulis) Inner side of the Shell (right valve) of the Fresh-water Massel CAmnionbn Inner side of the Shell (right valve) of the Marine Mussel (Mytilus) Transverse Section of Gill of Fresh-water Mussel (Anodonta) The Fresh-water Mussel. The Fresh-water Mussel dissected from the left side to sie the dubia structure The Marine Mussel dissected from the left side to show the general structure Shellremoved ' The Lancelet (Amphioxus lanceolatus) viewed from the left side Amphioxus dissected from the right side Transverse Sections of Aimphioxus The Spiny Dogfish (Acanthias, syn. Squalus) The Dogfish (Acanthias, syn. Squalus). Dissection The Skate (Raia). Dissection Urino-genital System of the Dogfish Dorsal View of the Pectoral Girdle and Fin Skeleton of the Skate Afferent Branchial or Ventral Arterial System of the Dogfish The Afferent Branchial or Ventral Arterial System of the Skate . The Dogfish (Acanthias, syn. Squalus). System . The Efferent Beanetival or Roma Aitorial cule of the Skate cad of the Dosti (Scyllium) Skull and Visceral Arches of the Dogfish (Soylliwm) as seen Hsia the left side The Brain, Cranial Nerves and Eye Muscles of the Dogfish Ventral View of the Brain of the Dogfish The Brain, Cranial Nerves, and Eye Muscles of the Skate The Frog (Rana). The Platana or Clawed Toad (Xenopus) Buccal or Mouth Cavity of Rana and of Xenopus Muscular System and Vascular System (part) of Rana and of Xenopus Dissection of Rana and of Xenopus, showing the Alimentary System Muscles of the Left Hind-limb of Rana and of Xenopus, from the Ventral Sunfeaa Efferent Branchial or Dorsal sean Muscles of the Left Hind-limb of Rana and of Xenopus, from the Dorsal Surface . Venous System (part) of Rana and of Xenopus, from the Ventral Aspect Dissection of the Leg of Rana and of Xenopus, from the Dorsal Surface . Arterial System of Rana and of Xenopus . : The Alimentary Canal of Rana and of Xenopus . The Urino-genital System (male) of Rana and of iee The Urino-genital System (female) of Rana and of Xenopus Pectoral Girdle of Rana and of Xenopus . F Pelvic Girdle of Rana and of Xenopus, side view . The Hind-limb and the Fore-limb of Xenopus The Vertebral Column and Pelvic Girdle of Rana and of ne Dorsal View of the Skull of Rana and of Xenopus 5 ‘i ‘Ventral View of the Skull of Rana and of Xenopus i . Side View of the Skull of Rana and of Xenopus . Spinal Nerves and nye Nervous lacs (left side only) of a and of Xenopus . The Brain and the sidiinal Cranial Nien of the Frog (Rana) . The. Pigeon (Columba). Dissection showing the principal Viscera PAGE 128 128 130 132 134 136 138 142 146 150 154 156 160 164 166 168 170 172 174 176 178 180 186 188 190 192 196 198 200 204 206 210 212 214 216 218 218 220 222 224 224 - 226 230 232 240 FIG. 86. 87. 88. 89. 90. 91. 92. 93. 94. 95. 96. 97. 98. 99. 100. 101. 102. 103. 104. 105. ILLUSTRATIONS The Pigeon. Dissection showing the Alimentary Canal, etc. . . 7 The Pigeon. The Vascular, Renal and Reproductive Systems . . The Pectoral Girdle, Sternum and Ribs ; and the Pelvic Girdle of the Pigeon . The Fore-limb of the Pigeon . : . é ‘5 . . The Hind-limb of the Pigeon . : : . ‘ 7 The Skull of the Pigeon F 3 . . . . The Rabbit (Lepus cuniculus). Dissection showing the Alimentary System, etc. The Rabbit. Dissection of the Neck and Thorax showing the lungs, etc. The Solar Plexus, and neighbouring structures, of the Rabbit . : The Rabbit. The veins and arteries of the Abdominal Region, and the Urino- genital System (male) . . - : i ; ‘i * The Skull of the Rabbit. Dorsal and Ventral View ‘ ‘ 5 * The Skull of the Rabbit. Lateral View : ; ° : Dorsal and Anterior view of the Atlas Vertebra of the Rabbit : . Left-side and Anterior view of the Axis Vertebra of the Rabbit : Left-side and Anterior view of the Sixth Cervical Vertebra of the Rabbit Right-side and Antérior view of the Fifth Thoracic Vertebra of the Rabbit . Right-side and Anterior view of the Second Lumbar Vertebra of the Rabbit The Rabbit. Left Scapula, left Humerus, and Skeleton of Fore-arm The Rabbit. The Sacrum, and the Pelvic girdle The Rabbit. Left Femur, left Tibia-fibula, and Skeleton of Foot Xi PAGE 244 248 252 254 258 262 276 280 282 288 294 298 298 300 300 302 302 306 308 312 THE PROTEUS ANIMALCULE (A4meba proteus) Ama@s# are found amongst debris deposits or on mud in fresh-water pools and slow-flowing streams. They are mostly invisible to the naked eye, rarely exceeding one quarter of a millimetre in diameter. Place a drop of water containing Amcebe on a slide, cover it with a cover- slip, and examine with the low power of the microscope. Form and General Structure. Note that the general form of Ameba is irregular and continually changing, the protoplasm flowing out into blunt processes called lobopods or pseudopodia, by means of which it moves and secures its food. Ectoplasm .. ‘ ‘Pseudopodia _- Nucleus Sand grains S fan enn an ween ee on ewee Food vacuoles 4 Contractile vacuole Fic. 1.—Ameba proteus (highly magnified). After Gruber. Examine the specimen under the high power and note the structure. The body is a naked mass of protoplasm, not uniform throughout, but showing two distinct portions : (a) The ectoplasm or ectosarc, a thin film, forming the clear outer portion of the body. (b) The endoplasm or endosare, forming the inner portion. It is granular, and the granules render the flowing movements of the protoplasm visible. Within it are seen the following structures :— (i) The nucleus, a spherical body, denser than the rest of the endoplasm. 4 THE PROTEUS ANIMALCULE (ii) The food vacuoles, spaces containing digestive fluid and ingested food material, ¢.g., diatoms, alge, etc. Grains of sand, fat globules, green vegetable organisms and other foreign bodies are also frequently present in the endoplasm. (iii) The contractile vacuole, a space filled with. a watery fluid. Evidently it functions as a drain for the finer wastes of the protoplasm. As it swells it is moved to the surface, and there contracts and discharges. The vacuole is formed anew, usually about the same position, when the effete liquid again gathers into a droplet. Make drawings of Ameba at regular intervals, noting the direction of the flow of the granules. The nucleus may be rendered more distinct by the addition of a drop of acetic acid. THE SLIPPER ANIMALCULE (Paramecium) Paramecium, one of the ciliate Infusoria, is a minute animal found in water in which decaying organic matter is present. It may be seen with the naked eye. A culture of Paramecia can be obtained by steeping hay in water and allowing it to decay, and by adding to this infusion some weeds from a fresh- water pond which contains Paramecia. Put a drop of water containing Paramecia on a slide, and place a cover-slip over it. Use a square cover-slip, and put a dot of soft wax on two corners at one side, so as to raise the slip slightly. Examine the slide under the low power. Form and General Structure. Note that the general form of Paramecium is definite ; it is roughly oval in outline, being somewhat rounded anteriorly and bluntly pointed posteriorly. Micronucleus J i Trichocysts Meganucleus ; oe Collecting canal Contractile Cilia : SS vacuole fli ' Myophan 5; H striations Food vacuole : 1 ; Mouth CEsophagus Fic. 2.—Paramecium caudatwm (highly magnified). After Butschli. i { Cortex Medulla Examine a Paramecium under the high power and note the following structures :— (a) The ectoplasm, ectosare or cortex, which consists of four layers : (i) The pellicle, the outermost tough investing layer, which gives definite form to the creature. (ii) The contractile layer of myoneme threads or myophan striations. (iii) The trichocyst layer. The trichocysts, minute spindle-shaped bodies, arranged side by side. When the animal is irritated, by adding a drop of very dilute acetic acid, each trichocyst discharges a very fine thread, very much longer than the cilia; and the creature is then clothed in a matted coating of fine hairs. The function of these trichocysts is protective. 6 THE SLIPPER ANIMALCULE (iv) The spongy layer, the innermost portion of the ectoplasm, in which fluid from the endoplasm collects. This fluid gathers particularly in two sets of radiating channels or collecting canals, and these drain off to form two large central drops, the contractile vacuoles. The formation or expansion (dia- stole) of each vacuole goes on until it comes into contact with the pellicle, then sudden contraction (systole) occurs, and the large spherical vacuole disappears. This process is repeated at brief intervals. The two vacuoles always re-form about the same position, between the centre and each end of the body. | The other structures connected with the ectoplasm are : (v) The cilia, numerous delicate vibratile filaments arranged in longitudinal rows over the whole outer surface. In the gullet specially large cilia adhere together and there form an undulating membrane. (vi) The oral groove or peristome, which begins near the anterior end of the Paramecium and leads to the mouth, which opens into the gullet. The food particles, carried in by the action of the peristome cilia, pass through the mouth into the gullet, and are there driven onward by the undulating membrane. The food vacuoles are formed at the bottom of the gullet and carried into the endoplasm. To see the formation of food vacuoles, put a drop of Indian ink at the edge of the cover- slip and watch the ingestion of the ink particles. (vii) The potential anus, a spot in the cortex, situated about midway between the mouth and the posterior end of the animal, and only visible when the waste products are extruded. (b) The endoplasm, endosare or medulla, which is granular and fluid, and which forms the central portion of the body. In the endosarc the following structures may be seen :— (i) The food vacuoles, spaces containing the particles of food. (ii) The macronucleus or meganucleus, a large ovoid body situated near the middle of the cell. This nucleus is concerned with the ordinary life of the body. (iii) The micronucleus, a very much smaller body lying at the side of the macronucleus. It is specialised for reproduction, Some species, e.g., Paramecium aurelia, have two micronuclei. Make a sketch of Paramecium. to show the above features. MONOCYSTIS —~ Monocystis, one of the Sporozoa, is a common internal parasite in the reproductive organs of the earthworm (Lumbricus). Cut open an earthworm (dorsal side) under salt solution. Open into the median seminal vesicles so as to expose the internal funnel openings of the vasa deferentia. Frequently Monocystis magna (one or several) is seen attached to the funnel by one end ; it looks like a tiny whitish thread. Form and Structure of Monocystis magna. Carefully remove a specimen, along with the portion of funnel to which it is attached, and place it in‘a drop of salt solution on a slide. Put on a cover-slip, and examine under low power. It is worm-like, and about a quarter of an inch long. Notice the clear thin Fic. 3.—Life-history Stages of Monocystis agilis (highly magnified). With permission from Parker and Haswell’s Teat-book of Zoology. A. Three trophozoites; B. Cyst containing two gametocytes; C. Stage prior to formation of gametes. Note the numerous small nuclei. D. Gametocytes broken up and gametes formed. Some of the gametes are conjugating in pairs, some pairs have fused to form zygotes; E. Cyst containing ripe spores or psendonavicelle ; F, A single spore or pseudo. navicella containing falciform sporozoites; G. A sporozoite inside a sperm-morula; H. A young trophozoite coated with tails of destroyed sperms. outer cortex of contractile ectoplasm, the outermost layer of which forms a stiff pellicle. The inner mass of endoplasm, the medulla. is finely granular and Io 12 MONOCYSTIS laden with reserve food substance; and within it there is a rounded, clear- looking fluid nucleus. This is the vegetative or trophic stage of the parasite, the trophozoite. Notice the characteristic ‘‘euglenoid ’? movement of Mono- cystis, which causes some variation in its long oval shape. Structure and Life-history Stages of Monocystis agilis. Monocystis magna may also be found free in the cavity of the seminal vesicles. In that situation, in well-infested worms, most of the life-history stages of a small species, Monocystis agilis, are generally present. With a pipette remove some of the fiuid contents of a seminal vesicle and put a drop of it, diluted with salt solution, on a clean slide. Cover with a cover- slip, and examine the slide under the microscope. The fluid chiefly consists of countless hair-like spermatozoa and numerous sperm-morula—i.e. mulberry- like clusters of developing spermatozoa—and these form the normal contents of the seminal vesicles. Amidst the sperms and morule the following Monocystis stages may be seen :— (a) Free adult trophozoites (Fig. 3, 4), in form and structure similar to those of M. magna, as noted above. (6) Trophozoites which, having attained the limit of growth and being ripe for reproduction, have rounded themselves off and become gameto- cytes. These may be seen in closely associated pairs, or at the more advanced stage of (c) Paired gametocytes within a cyst (Fig. 3, B) which they have secreted. (d) Cyst containing two gametocytes about to form gametes. Note the numerous small nuclei which have been formed and moved towards the surface of the body (Fig. 3, C). (e) Cyst showing the gametocytes broken up into small portions, each con- taining a nucleus; these are the gametes (Fig. 3, D), some of which are seen in conjugation, and some pairs are already fused and therefore zygotes. Notice that there is in the cyst a certain amount of residual protoplasm, which serves for the nourishment of the gametes. (f) Clear bluish cysts containing numerous small boat-shaped spores or pseudonavicelle (Fig. 3, Z). The zygotes become ovoid and secrete tough chitinous coats, and by division each segments into a cluster of eight sausage-shaped sporozoites surrounding a small amount of residual protoplasm. In that way the zygote is transformed into a spore (Fig. 3, Hand F). These spores must be transmitted to another host before they/can develop further. Probably the earthworm is eaten by a bird, and the spores passed out undigested along with the excreta. The spore may then be swallowed by another worm; and the spore-coat being dissolved by the digestive juices, the sporozoites will therefore be set free. From the food-canal they find their way into the seminal vesicles, and they enter the sperm-morule. (g) A sporozoite inside a sperm-morula (Fig. 3, G). It derives nourish- ment from the surrounding protoplasm and develops into a young trophozoite. (h) Young trophozoites coated with sperms (Fig. 3, H). SPONGES (Porifera) As different species of Sponges can usually be obtained in the fresh con- dition for examination, no particular type has been selected for description ; but a general account of sponge structure is given as a guide to the practical examination of the type available. Form and General Structure. Sponges are sedentary (except in the larval state), and live attached to the surfaces of rocks, weeds, etc. They are aquatic and mostly marine, and they have a plant-like appearance. Some are solitary, many are colonies of ‘individuals ”’ closely grouped or compacted together. These colonies are formed by vegetative budding from a creeping stolon, and become more or less complex by branching. The great differences in size, form and appear- ance among sponges are largely due to the nature of the budding. The Endoderm Spicules h i a aa iu ANABD DINSEsvIEg oy Spicules ‘ : ids ——— 4 Prosopyle : Mesogloea Eeioderm Fic. 4.—Transverse Section through a part of the wall of Sycon gelatinosum. After Parker and Haswell. simplest types are tubular in form (e.g., Leucosolenia, a simple Ascon sponge), or sac-shaped (e.g., Grantia, a Sycon sponge). The body of a sponge is a system of canals or waterways; the water passes in through numerous minute inhalent pores in the body-wall, and, after circulating throughout the internal cavity or cavities, it passes out at one or several large exhalent openings or oscula. The chief internal differences in sponges are seen in this canal system, of which there are distinct types. Otherwise the structure of the body is similar in all the sponges. 14 16 SPONGES Sponges are two-layered (diploblastic) Metazoa. The two layers are the outer dermal layer (“‘ ectoderm ”’), which consists of flattened epithelial cells and pore-forming porocytes, and the inner gastral layer (‘‘ endoderm ”’), which is composed of flagellate collar-cells or choanocytes. Between the layers is a middle jelly (mesogloea) containing wandering amcebocytes, some of which form the characteristic limy or siliceous spicules of the supporting skeleton. (a) The Dermal Layer or “ Ectoderm.” This covers the outer surface of the sponge, and is composed of flattened epithelial cells, with porocytes here and there. The porocytes are cells which become hollowed out and thus form the temporary inhalent pores. The epithelial cells (dermal epithelium) take the form of thin scales, so closely cemented together by their edges that their boundaries are not readily distinguishable—i.e. they form a syncytium. In sponges which have more or less complex canal systems, formed by outgrowths and foldings of the body-wall, portions of the dermal layer are internal and line the inhalent or incurrent canals. Groups of spicules project through the dermal layer. (6) The Gastral Layer or ‘‘ Endoderm.” This layer lines the gastral or paragastric cavity (in the simplest sponges) and the radiating chambers or radial canals (in the higher types). The cells of the gastral cavity (in the higher types) are thin epithelial cells; those of the radiating chambers are collar-cells or choanocytes. The collar-cells are flask-shaped ; each has a nucleus, a long whip-like flagellum projecting from the free end, also a delicate collar which surrounds the lower portion of the flagellum. The collar is retractile, and the flagellum also can be withdrawn. (c) The Middle Jelly or ‘‘ Mesogloea.”’ This gelatinous matrix, situated between the two layers, contains wander- ing amoeboid cells or amcebocytes. The amcebocytes probably serve as carriers of food and removers of waste; but some of them develop into genital cells, and others become scleroblasts or spicule-forming cells. The spicules are embedded in the jelly matrix, and in certain sponges are felted together into a supporting skeletal framework. There are various kinds of spicules, viz. :— (i) Monaxon spicules, having a needle-like form with a single axis. (ii) Triaxon spicules, consisting of four radii of a sphere, meeting each other at equal angles at the centre and thus producing a four-rayed form. (iii) Polyaxon spicules, which have numerous axes typically radiating out from a common centre. Further variations occur in some sponges, giving rise to the following sorts :— (i) Triradiate spicules, consisting of three rays branching from a common centre in the form of a tripod. 18 SPONGES (ii) Anchor spicules, having the form of an anchor. ; (iii) Amphidisc spicules, consisting of a rod bearing at the distal Fic. 5.—Types of Sponge Spicules. After J. Arthur Thomson. 1, Monaxon ; 2, triradiate ; 3, triaxon; 4, tetraxon; 5, anchor; 6, polyaxon; 7, an amphidisc. extremities disc-like expansions curved towards the centre and prolonged into several tooth-like protuberances. The Main Types of Canal-system. All the cavities of the body traversed by the currents of water which nourish the sponge are termed collectively the canal-system. This system attains a high degree of complexity, and four different types may be distin- guished according to the situation of the choanocytes : 1. The Ascon Type. The canal-system is simple. The water enters through the numerous temporary inhalent pores in the body-wall into the central gastral cavity of the tube. at the top of which is the exhalent osculum, through which the water passes out. The choanocytes line the gastral cavity. Examples: Leucosolenia, Clathrina (Class, Calearea; Order, Homoceela). (See Fig. 6.) 2. The Sycon Type. This type arises from the Ascon type by a process of outgrowth and fold- ing of the body-wall, resulting in the formation of a number of blind diverti- cula of the gastral cavity and the restriction of the choanocytes to the interior of these diverticula, which are therefore called the flagellated or radiating chambers (radial canals). The gastral cavity is lined by flattened epithelium derived from the dermal layer. Between the radiating chambers canals are enclosed, from which the water flows into the chambers. These are called the incurrent or inhalent canals, and are lined by the flat epithelium of the 20 SPONGES dermal layer. The inhalent canals open to the exterior by the ostia, and also communicate with the radiating chambers by means of small apertures, the prosopyles. The radiating chambers open into the gastral cavity through the apopyles. Thus the water enters the ostia or inhalent pores into the ieee Middle Jelly oe ean a \C a Ameebocyte o. . a i . 4 Dermal Epithelium ce ar “a a Collar-Cell Hg on er, Nigee Nose ane + 2 Choanocytes Scleroblasts Spicules Inhalent Pore Porocyte Fic, 6.—Transverse Section of an Ascon Sponge (diagrammatic). After J. Graham Kerr, incurrent or inhalent canals ; thence it passes through the prosopyles into the radiating chambers or radial canals, and from these it goes through the apopyles into the gastral or paragastric cavity and out by the exhalent osculum. Example: Sycon (Class, Calearea; Order, Heteroccela). (See Figs. 4 and 7.) 8. The Leucon Type. By a further process of folding this type is derived from the Sycon type, the result being that diverticula of the gastral cavity arise and into each diverticulum several radial canals open. Thus the primary incurrent canal communicates’ by means of secondary inhalent canals, from which the prosopyles arise, with a secondary radial canal lined by choanocytes, which, opens by an apopyle into the primary radial canal or radiating chamber. All the primary radial canals open into the gastral cavity. Therefore the water enters through the ostia’into the primary incurrent canals; thence it 22 SPONGES goes into the secondary incurrent canals and through the prosopyles into the secondary radial canals ; from these it passes by the apopyles into the primary Prosopyle Radiating Chamber Pore or Ostium Inhalent Canal Fig. 7.—Transverse Section of a Sycon Sponge. The central space is the gastral cavity. From Masterman’s Text-book of Zoology. radial canals, and so into the gastral or paragastric cavity. Example: Leucilla (Class, Calcarea ; Order, Heteroccela). . Primary Radial Canal =“5~—-. primary Inhalent Canal “Secondary Inhalen Canal P mS Secondary Radial Canal or Radiating Chamber Fic. 8.—Transverse Section of a part of the wall of a Leucon Sponge. From Masterman’s 1'ext-book of Zoology. 4, The Rhagon Type. This type resembles the last one and can be derived from it. Here the primary incurrent canal communicates by the prosopyle with the secondary radial canals, which take on a rounded shape and are lined by choanocytes. 24 SPONGES From these the apopyles open into the primary radial canal, which is in com- munication with the gastral cavity. Thus water enters through the ostia ; Primary Radial Canal ___, Secondary Radial Canal or Radiating Chamber “~ Prosopyle “\ Middle Jelly ” Apopyle Dermal Epithelium Fic. 9.—-Transverse Section of a Rhagon Sponge. From Masterman’s Text-book of Zoology. thence by the prosopyles into the secondary radial canals ; and from these by the apopyles into the primary radial canals, and so into the gastral cavity. Example: Oscarella (Class, Demospongie ; Order, Myxospongida). THE FRESH-WATER POLYP (Hydra viridis) Hydra is a small fresh-water animal, occurring in lochs, ponds, ditches, etc. If a glass jar is filled with some water and weeds collected from a pond and allowed to stand for a while undisturbed, then there may be seen little whitish or green bodies, from 2 to 6 mm. in length, adhering to the weeds = TS gy AR ERR, & bf OE A se ee AG 4 YOR Sig ~Tentacle fi A Yh way ae ay 7 ay Ny LY Bey AN LE * f ARN we Hypostome aN 4 Be GES - ‘Testis Ectoderm- ¥ : ms Bud -- F ndoderm - gee) f aa : Be (PER Bud ae ne “PSR -Enteric cavity ui Le D> A 4 Se Gag Wa: Bp (B® a WS ES 2g CORA ES oe Sia aS eB PR, : a SB i, aah Mesogloea:---# fe B. aS 2 ne CREA Fie. 10.—A. Hydra viridis x 10; B. Longitudinal Section of Hydra viridis. After Parker and Haswell. or to the sides of the jar. Cut off a piece of weed to which a Hydra is adher- ing, or remove one with a pipette or a dipping tube, and place it on a slide in a drop of water. Cover with a supported cover-slip, and examine under the low power of the microscope. A, General Form and External Features. Hydra, when fully extended, has a long and slender thread-like appear- ance, Its tubular body is attached at one end by a flattened basal disc. 26 28 THE FRESH-WATER POLYP The free end bears a circlet of six or more tentacles, which are hollow pro- longations of the body. At the top of the tube, and surrounded by the tentacles, is a low conical projection, the oral cone or hypostome, in the centre of which is the circular mouth aperture. At the sides of the body projections or bulgings may be seen; these may be daughter buds at various stages of development, or they may be the developed reproductive organs. The animal is hermaphrodite; the testis is situated near the mouth end, while the ovary is usually near the “foot” or base of the body tube. Notice the clumps or batteries of stinging cells (nematocysts) studding the tentacles. Make a drawing of Hydra to show the above features. B. Microscopic Structure. Examine a longitudinal and a transverse section of Hydra under the low power, and note that the body-wall has the following layers :— (a) The ectoderm, a thin layer of many cells packed tightly together, forming a protective covering for the body. (b) The endoderm, a thick layer of larger columnar cells lining the. coelenteron or enteric cavity. (c) The mesogloea or supporting lamella, apparently structureless, be- tween the ectoderm and the endoderm. Note the ccelenteron, enteric or digestive cavity occupying the centre of the body. The mouth leads into the ccelenteron, which extends into the tentacles, these being hollow processes, and also into the buds. Make a drawing of a longitudinal section and a transverse section of the body. . Examine the layers of the body-wall under the high power and note the component cells : (a) The ectoderm. This layer is made up of large ectoderm cells, somewhat conical in shape, arranged side by side and with their broader ends outwards. Each of these cells has a nucleus and a very large vacuole (not shown in Fig. 11, B and C); and the tapering end of the cell is drawn out into crosspiece processes which contain contractile fibrils. These muscular processes le alongside the mesogloea and (in trvanserse sections) are just visible as minute dots. The ectoderm cells are therefore myo-epithelial cells. The spaces between the inner and narrower ends of the ectoderm cells are filled up with small and round interstitial cells. Some of the interstitial cells become specialised for reproduction and give rise to the testis (one or more) by a proliferation forming a small conical heap projecting externally and covered by the ectodermal cells. The ovary is similarly formed; at first it contains several ova, but ultimately only one large ovum remains. Embedded in and between some of the large ectoderm cells there are clear oval sacs with well-defined walls. These are the stinging ceils, thread cells, or nematocysts ; and each consists of a tough sac, the neck of which is turned outside in as a hollow pouch. The free end of the pouch is continued into a 30 THE FRESH-WATER POLYP hollow and coiled filament, and from its inner surface project the barbs. The nematocyst, which contains a fluid, lies in a special interstitial cell known as the cnidoblast. The cnidoblast contains a hollow sac, and in this sac the nematocyst lies. The free end of the cnidoblast is produced into a delicate pointed process, the enidocil or “‘trigger-hair.” The slightest touch of the cnidocil causes sudden contraction of the cnidoblast, anid the pressure (possibly Nematocyst erry - Endoderm i a5 Enteric Interstitial cells - cavity Ectoderm Fic. 11.—A. Transverse Section of Hydra viridis (greatly enlarged) ; B. Small part of the body- wall highly magnified ; C. Two isolated ectoderm cells ; D. Cnidoblast, before the extrusion of the nematocyst thread; E. Cnidoblast, after the extrusion of the nematocyst thread. C.-E. after Parker and Haswell. through contact with the water) causes the instant eversion and extrusion of the nematocyst neck and thread. There are small nerve cells connected with the enidoblasts. (b) The endoderm. This layer is made up of large endoderm cells lining the ccelenteron ; these are similar in shape to the ectoderm cells, and each has a nucleus, a large vacuole, and also either pseudopodia or two flagella which project into the coelenteron. The endoderm cells also have crosspiece muscular processes, and are therefore myo-epithelial cells. The muscular processes run circularly, and can be properly seen only in longitudinal sections. Some of the endoderm cells near the mouth are specialised as gland cells, which secrete a digestive ferment. There are also gland cells on the ‘‘foot” or base of Hydra, and their sticky secretion probably enables it to attach itself firmly to surfaces. The green 32 THE FRESH-WATER POLYP colour of Hydra viridis is due to numerous green symbiotic Flagellates which are present in the endoderm cells. (c) The mesogloea. This is a thin, structureless lamella, forming a sort of strengthening sheath. On the outer surface a distinct longitudinal striation is formed by the muscle processes of the ectoderm cells. On the inner surface transverse fibres occur, which appear to be connected with the muscle processes of the endoderm cells. Make a drawing of a small part of the body-wall to show the layers and the component cells. Put a drop or two of acetic acid and methylene blue at the edge of the cover- slip, and observe the extrusion of the nematocysts. Notice that some of them (small ones) are without barbs. Then gently tap the cover-slip, so as to break up the dead Hydra; and examine and draw the isolated cells. Two Ciliate Infusorians are often seen moving about on the skin of Hydra, namely, Kerona, a commensal, and Trichodina, an ectoparasite. THE SEA-ANEMONE (4ctinia) External Features. The Sea-anemone has the form of a cylinder, the height of which slightly exceeds the diameter. The cylinder or column is fixed by its broad base. At the free end the column passes into a horizontal plate, the disc or peristome. In the middle of the disc is the slightly elevated slit-like mouth. Arising from the disc, and encircling the mouth, are numerous short tentacles regularly arranged in circles. There is a pore at the tip of each tentacle through which water may be passed. Directive mesentery Genital organ Mesenteric filament f 3 ‘ emannsear serreee Longitudinal muscle _ ( ~Tertiary-” : -mesentery a Siphonoglyph Fic. 12.—A. Transverse Section through the gullet region (stomodzum) of a Sea- anemone ; B. Transverse Section below the gullet, about the position indicated by the arrow in Fig. 13, A. General Structure (Transverse Section). If a transverse section is made across the column a short way below the tentacles the following structures will be seen :— (a) The body-wall, composed of ectoderm, mesogloea and endoderm. (i) The ectoderm consists chiefly of ciliated, sensory, stinging and gland cells, and also of numerous muscle cells. (ii) The mesogloea is a tough and fairly thick supporting tissue between the ectoderm and endoderm, and it forms the basis for their cells. It contains amoeboid cells which have wandered into it from the ectoderm chiefly ; it is therefore mesenchyme tissue or incipient mesoderm. (iii) The endoderm consists mainly of flagellate cells, with muscular fibres at their roots. 34 36 THE SEA-ANEMONE (b) The gullet or stomodeum. This has the form of a flattened cylinder hanging down into the interior of the body. It is marked with longi- tudinal grooves, two of which, termed the ciliated grooves or siphono- glyphs, occur at the ends of the long diameter of the gullet, and correspond to the corners of the mouth. They are broad and deep and sometimes bear cilia. The gullet is composed of ectoderm, mesogloea and endoderm. (c) The mesenteries. These consist of supporting mesogloea, covered on both sides with endoderm. Muscles occur on the mesenteries which are divisible into the following groups :— (i) Primary mesenteries, usually twelve in number, all reaching to the gullet. They are arranged in six pairs. The cavity en- closed by each pair is known as the intraseptal cavity; the cavity between adjacent pairs is the interseptal cavity. The two pairs attached to the siphonoglyphs of the gullet divide the animal into bilaterally symmetrical halves and are called the directive mesenteries. The retractor or longitudinal muscles on these directives are turned away from each other, and are within the interseptal spaces; while on all the other mesenteries the muscles are facing, and’ within the intraseptal spaces. (ii) Secondary and tertiary mesenteries arise later in the inter- septal chambers and are short, not reaching to the gullet. In all these the longitudinal muscles of each pair face each other. The gonads or reproductive organs are developed in the substance of the mesenteries, and are derived from the endoderm. Longitudinal Section. In a longitudinal section the following features may be seen :— (a) The body-wall, consisting of ectoderm, mesogloea, and endoderm. (6) The basal disc, similar to the body-wall, by which the animal fixes itself. _ (c) The gullet, with the longitudinal ridges. This hangs down into the body and terminates in a free edge produced at each end of the long diameter into a descending lobe or lappet. (d) A primary mesentery. Its upper half is attached to the gullet, its lower half is free. It is attached to the basal disc and to the body-wall. In development it arises as a growth from the body-wall to the gullet. An aperture, the ostium, occurs in the mesentery and places the adjacent compartments of the enteron in communication. (e) A secondary and a tertiary mesentery. These do not reach the gullet, their edges are free in the enteric cavity. (f) The mesenterial filaments on the free edges of the mesenteries. Gland cells, which secrete a digestive ferment, are present in the epithelium of these filaments. 38 THE SEA-ANEMONE (g) The acontia, long delicate threads springing from the edges of the mesenteries ; they bear nematocysts, and can be protruded through minute apertures in the body-wall known as cinclides. (h) The genital organs or gonads on the primary mesenteries. (t) The muscles of the mesenteries. These are: (i) The longitudinal or retractor muscle, a narrow band stretching from the base to the disc on one side of each mesentery. (ii) The parietal muscle, passing obliquely across the lower angle of the mesentery. (j) There is a circular sphincter muscle around the oral margin. Gullet-- ern EK - Secondary } mesentery Primary mesentery--l-|- -- Longitudinal muscle----- | Mesenteric : filament----- Genital organ- Mesenteric filament--- - Basal disc Fic. 13.—A. Longitudinal Section of a Sea-anemone (at the position indicated by the arrow in Fig. 12, B.); B. Longitudinal Section (diagrammatic) of a Sea-anemone. THE LIVER-FLUKE (Fasciola or Distoma hepatica) Tue adult Liver-fluke is commonly found in the bile-ducts of the sheep. It causes the disease known as “ liver rot.” . External Features, It is an unsegmented and flattened worm, leaf-like in form and about an inch long. At its broader end it has a triangular projection, the head-lobe or cephalic cone. The surface of the body is devoid of cilia, but is covered by minute spines pointing backwards. At the tip of the head-lobe is the small cup-shaped anterior sucker with the mouth in its centre. On the ventral surface is the ventral sucker, situated just behind the head-lobe. The genital aperture is situated between the anterior and the ventral suckers, but nearer the latter. The excretory pore lies in the middle of the posterior end of the body, slightly on the dorsal surface. Alimentary System, In order to make out this system clearly, the fluke may be injected through the mouth with a solution of Prussian blue. It should then be placed between two slides, tied together, so as to flatten it. Put the slides with the fluke into 90 per cent. aleohol for about twelve hours, and then dehydrate, clear, and mount in balsam. The mouth leads into a small ovoid muscular pharynx. From this a short cesophagus leads to the intestine, which immediately divides into two parts, each giving off a number of blind pouches or ceeca. The intestine ends blindly posteriorly, there being no anus. Excretory System. This may be seen by an injection (similar to that in the case of the alimentary system) made in the middle line of the body near the excretory pore. It consists of a longitudinal main trunk opening at the posterior end by the excretory pore. The trunk is formed from the union of two anterior ducts on each side. The posterior two are dorsal, the anterior two are ventral. These ducts are formed from smaller ducts, and these in turn from numerous capillary tubules, each of which begins with a flame-cell or excretory cell. Reproductive System. This system is complicated. The animal is hermaphrodite. 1. Female. The ovary is a branched and unpaired organ lying in the anterior part of the body on the right side. A short and narrow oviduct leads from the ovary towards the middle line to join the median yolk-duct or vitellarian duct, which is formed by the union of two transverse ducts leading from the junction of the two long lateral ducts on each side. These are formed from the numerous 40 42 THE LIVER-FLUKE ductules of the diffuse system of yolk-glands along each side of the body. The oviduct and the median vitellarian duct are surrounded at their junction by the shell-gland ; and these united ducts form the wide convoluted uterus which opens (beside the penis) into the common genital outlet. A short tube, known as Laurer’s canal, runs from the junction of the oviduct and the median vitellarian duct and opens by a pore on the mid-dorsal surface. 2. Male. This system consists of a pair of much-branched testes lying in the middle of the posterior half of the body. The branches of each testis open into a vas Mouth Month ie -Pharynx -Supra-cesophageal Subcesophageal ganglion ‘ganglion-------7 Penis--- Vesicula seminalis~ Anterior nerve - £e perture AS = Posterior nerve-, y --7Parenchyma of body “Uterus --Ventral branches of Excretory canal Vas deferens -Shell gland Ovary -~ Alimentary canal Oviduct” -Excretory canal 2-Testis '=*Dorsal branches of Excretory canal “Vitelline duct Vitelline glands-.- - - - ‘-Excretory pore Fic. 14.—A. Dorsal View of the Liver-fluke (Fasciola hepatica), showing the alimentary canal and the excretory system ; B. Ventral View, showing the reproductive system ( x 4). deferens, the two vasa deferentia running forward to the cirrus-sac (a depression between the ventral sucker and the genital aperture or outlet) and there uniting to form an elongated sac, the vesicula seminalis. From this a fine duct, the ductus ejaculatorius, runs forward into a muscular organ called the penis or cirrus. This opens by the small male genital pore in the common genital aperture or outlet. The penis is evaginated, when the sperms are ‘expelled, and the ejaculatory duct is then telescoped inside it. Nervous System. This consists of a ring round the cesophagus with two lateral ganglia and a single ventral ganglion on it. Nerves are given off from the ganglia to the anterior region of the body, and from each lateral ganglion a lateral nerve runs backwards under the ceca of the alimentary canal to the posterior end of the body. 44 THE LIVER-FLUKE Transverse Section of Body. In a transverse section through the body (as indicated by the arrows in Fig. 14, A and B) the following structures will be seen :— (a) The cuticle, a homogeneous layer with spinules developed in it. (6) A layer of circular muscles. (c) A layer of longitudinal muscles. Spinules e- % Longitudinal muscles f Vitelling glands Ectoderm Cuticle Excretory canal Vv ‘ ‘ n ue o fs ’ Vitelline duct \ ‘Circular gaustles , ' + deeral nerve “A . Vas eheceiin ' Ovary Alimentary canal y Parcuchigiie teria Fic. 15.—Transverse Section through the body of a Liver-fluke (at the position indicated by the arrows in Fig. 14, A and B). (d) The spaces between the various organs, filled by a peculiar form of connective tissue, the parenchyma. (e) The intestine with the lateral ceca. (f) Vitellarian ducts and yolk-glands. 4 (g) The uterus. (h) The ovary. (t) The vasa deferentia. (7) The excretory ducts. (k) The lateral nerves. - THE TAPE-WORM (faenia) VaRious species of tape-worms are parasites in the alimentary canal of Vertebrates. Two of the commonest species are T'aenia serrata, which is found in the dog, and T'aenia or Dipylidium caninum, which is found in the dog and Proglottides approaching Young maturity Proglottides Ripe or Gravid Proglottis “ Head” Scolex Fic. 16.—The Beef Tape-worm (Taenia saginata). Selected portions of a single specimen. After Leuckart. also in the cat. Portions of these tape-worms are generally discharged with the faeces of the host, and thus may easily be obtained. Complete specimens may be procured by cutting open the intestine of dogs or cats which have been destroyed. Form and General Structure. The Tape-worm has the form of a long segmented ribbon. Towards the anterior end the ribbon becomes much narrower, and at this end the extremely 46 48 THE TAPE-WORM small ‘“‘head”’ and scolex are situated. The rest of the animal is called the body or strobila. The top of the scolex is the somewhat conical rostellum, the base of which expands into the rounded ‘“‘head.” The rostellum has a circlet of minute recurved hooks, and the head bears four rounded suckers. By means of these hooks and suckers the tape-worm attaches itself to the lining of its{host’s intestine. The body or strobila is made up of a series of segments or proglottides. These are narrower behind the head region and gradually increase in size towards the posterior end. Each proglottis, when mature, contains a set of hermaphro- dite reproductive organs. At first the male organs alone are developed, then the female organs appear ; and later the whole segment, on the ripening of the female organs, is filled with developing eggs or embryos, and only remnants of the male and female organs, except the uterus, remain. Uterus aT Trine TTT TTT Rh 0 ep oa \ PSSA OE Tar SCN SV, AT al ES 4 ~ YT 4 it r= a ~ \ is } ; a SS, (4 Gal G58 | $F ots een ctetors canal i + ay fi \ Le i 4 Fic. 19,—KEarth-worm (Lumbricus terrestris). A. Dorsal View of the first 40 segments; B. Ventral View of the first 17 segments; C. Ventral View of the last 6 segments; D. Lateral View of the first 16 segments. 54 56 THE EARTH-WORM (c) The capsulogenous or spermaducal glands, situated on the ventral surface of the 9th, 10th, and 11th segments. (d) The openings of the oviducts, on either side of the median line, in the 14th segment. (e) The openings of the vasa deferentia, slit-like apertures with tumid lips, on either side of the median line, in the 15th segment. 3. Make a drawing of the side showing : (a) The lateral setz. (6) The openings of the spermathece, situated in the grooves between the 9th and 10th, and the 10th and 11th segments. General Structure. Pin the worm down, under water or in salt solution, by inserting a pin through the prestomium and one through the last segment so that the dorsal surface is uppermost. Cut along the mid-dorsal line from the 25th to the 1st segment and reflect the body-wall, placing pins obliquely through it on each side. Put a pin through each side of the 18th segment. Note the mesenteries or transverse septa dividing the ccelome into a series of compartments. In each segment, except the first three and the last, there is a pair of nephridia, one on either side of the alimentary canal, opening to the exterior by the nephridiopores, which are situated near the ventral chetz. A, The Alimentary System. The mouth leads into a short buccal cavity. Following this is a stout muscular pharynx, which extends from about the 3rd to the 6th segment. The pharynx is attached to the body-wall by radiating muscular strands. Succeeding the pharynx is the cesophagus, a straight and narrow tube extending to the 14th segment. There are three pairs of cesophageal pouches or calci- ferous glands, one pair in the 11th and two pairs in the 12th segment. The cesophagus expands into a thin-walled crop in the 15th and 16th segments. The crop is succeeded by the gizzard, with thick muscular walls, which extends to about the 19th segment. Following the gizzard is the long straight intes- tine, which leads back to the anus, the terminal opening at the posterior end of the body. The intestine is surrounded by a layer of ‘ yellow-cells ” (coelomic epithelium). B. The Vascular System (Principal Blood-vessels). The dorsal blood-vessel lies above the alimentary canal and extends along the greater part of its length. Anteriorly it gives rise to smaller blood-vessels, which extend over the dorsal surface of the pharynx. In each of the segments, 7 to 11 inclusive, the dorsal vessel gives rise on each side to a smaller vessel, which curves round the cesophagus and leads into the sub-intestinal or ventral vessel. These six half-hoop-like vessels are spoken of as ‘hearts.’ The ventral vessel lies between the alimentary canal and the nerve cord, and extends along the course of the nerve cord. It may readily be seen by pushing the alimentary canal to one side. Make a drawing to show the alimentary and the vascular systems. 58 THE EARTH-WORM C. The Nervous System. Cut through the anterior end of the oesophagus and carefully remove the whole alimentary canal posterior to this. Push the pharynx over to one side so as to expose the nervous system. The “brain ” is situated on the anterior part of the pharynx in the second segment of the body, and consists of a pair of supra-pharyngeal ganglia. Hach ganglion gives off ‘nerves to the prestomium. These ganglia are connected (by 1 Subpharyngeal Pharynx -- Esophagus -7-Nephridia 5 Ventral nerve cord 7 Vesicule seminales 9 fr -—------ Dorsal blood -Spermatheca ~Wesicu. /seminales sperm Atl ses T Crop reservoir 11 Vas deferens +7})---Gizzard -Posterior sperm, reservoir 13 14 Fic, 20.—A. Alimentary and Vascular Systems of Earth-worm (Lumbricus); B. Nervous and Reproductive Systems. a pair of cireum-pharyngeal commissures passing round each side of the pharynx) with a pair of sub-pharyngeal ganglia lying in the 4th segment. From them the ventral nerve cord is continued straight back in the middle line to the posterior end of the body. The ventral nerve cord is double, but the cords are more or less fused together. In each segment the cord swells to form a ganglion, which gives off three pairs of nerves, one pair near the anterior septum and two pairs near the posterior septum. D. The Reproductive System. The Earth-worm is hermaphrodite. The reproductive organs and ducts are situated in segments 9 to 15. The ovaries are a pair of small pear-shaped bodies lying in the 18th segment, one on either side of the nerve cord. Each is attached to the posterior face of the septum between the 12th and 18th segments. Facing the ovaries, in the same segment but on the septum behind, there are two wide ciliated funnels; these are the internal coelomic openings of the oviducts. Each oviduct passes through the septum between the 18th and 60 THE EARTH-WORM 14th segments, and opens to the exterior by the female genital aperture on the 14th segment. The vesicule seminales or sperm-sacs lie above the nerve cord in segments 9 to 12, and completely cover in the testes and the internal openings of the vasa deferentia. Each seminal vesicle consists of two parts, a spacious median un- paired sac or sperm-reservoir, and paired lateral expansions of these, the seminal vesicles proper. These expansions are seen on opening the worm, appearing as three pairs of sacs at the sides of the alimentary canal. The anterior median seminal vesicle lies in the mid-ventral part of the 10th segment ; and its four corners are produced into pouches, the pair of anterior lateral seminal vesicles,. which extend from the 10th segment and occupy the cavity of the 9th, and the first pair of posterior lateral seminal vesicles, which push backwards and occupy the cavity of the 11th segment. The posterior median seminal vesicle lies in the mid-ventral part of the 11th segment, and it has only one pair of pouches —namely, the second pair of posterior lateral seminal vesicles, which extend so far back as to occupy the 12th and 18th segments. Carefully remove the vesicles of one side so as to expose the testes and the internal funnels of the vasa deferentia. The testes are two pairs of small bodies attached, on either side of the nerve cord, to the posterior faces of the septa separating the 9th and 10th and the 10th and 11th segments. Immediately behind each testis lies a large ciliated funnel, the internal opening of a seminal duct. On each side the seminal duct of the anterior testis passes backwards through the septum separating the 11th and 12th segments, and is joined in segment 12 by the seminal duct of the posterior testis. The two ducts form the vas deferens, which passes through the successive septa to segment 15 and there opens to the outside by the male genital aperture. In the 9th and 10th segments there is a pair of small white spherical sacs, the spermathece or receptacula seminis, opening by pores between segments 9 and 10, and 10 and 11. Make a complete sketch showing as much as possible of the reproductive and nervous systems. Transverse Section of Body. In a transverse section of the body of the Earth-worm the following structures will be seen :— (a) The thin cuticle. (b) The epidermis, consisting of a single layer of cells. (c) The dermis, a very thin layer of connective tissue. (d) The circular muscles. (e) The longitudinal muscles, arranged into seven bundles. (f) The set or cheetee. situated in special setigerous sacs formed from the epidermis. (g) The coelome or body-cavity, the space between the body-wall and the alimentary canal. (h) The intestine, which is coated externally with the ‘ yellow-cells ”’ or ccelomie epithelium. It has a deep dorsal fold, the typhlosole, pro- jecting downwards into the cavity of the intestine. This fold is filled 62 THE EARTH-WORM with ‘ yellow-cells.” The wall of the intestine is composed of a muscular layer, and is lined with ciliated epithelium. ; (i) The dorsal blood-vessel, lying in the “ yellow-cells ” above the intestine. (j) The ventral or sub-intestinal blood-vessel, lying beneath the ae : (k) The ventral nerve cord, lying beneath the ventral blood-vessel. Jus beneath the nerve cord is the sub-neural vessel. (1) Portions of the septa, and portions of nephridia. Dorsal Vessel Nephridium "rie External Aperture of — A Nephridium(nephridiopore) Celome Sete Ventral Vessel Sub-neural Vessel Fic. 21.—Transverse Section (diagrammatic) through the middle of the body of the Earth-worm (Lumbricus), A nephridium is shown (entire) on the left side of the figure, and setz on the right side. After Marshall and Hurst. With permission from Parker and Haswell’s Text-book of Zoology. Carefully remove one of the ovaries, along with the portion of the septum to which it is attached and with the attached nephridium. Mount on a slide in salt. solution, and examine with a low power. Notice the ripe ova in the thin. distal end of the pear-shaped ovary. The nephridium is tubular and consists of a very small ciliated funnel, a looped main portion which is glandular and solid (the duct passes through the cells), and a much wider and non-glandular bladder which opens to the exterior. The bladder has muscular walls, and within it may be seen parasitic Nematode worms. The ciliated funnel opens into the ccelome or body-cavity, and this internal opening is the nephrostome. Notice the blood capillaries on the walls of the nephridium. The contents of the seminal vesicles and the spermathece should be examined under high power. The first contain developing spermatozoa, and the second have ripe spermatozoa received from another worm. NotE.—The South African Earth-worm (Chilota) is very suitable for dis- section, especially with reference to the reproductive system, and should therefore be studied by senior students if possible. THE MEDICINAL LEECH (Hirudo medicinalis) External Features. 1. Make a drawing of the ventral surface of the Leech showing :— (a) The body divided by a series of transverse furrows into a definite number of annuli (about ninety-five). The annuli are more numerous than the true segments of the body; and, except at the two extremities, each segment contains five annuli. The anterior annulus of each seg- ment bears six sensory papilla, both dorsally and ventrally. A pair of nephridiopores occurs on the posterior annulus of each segment, from the 6th’ to the 22nd inclusive. Thus the sensory papillze determine the anterior border of each segment of the body, while the nephridio- pores determine the posterior border of segments 6 to 22. There are five segments in front of the one bearing the first pair of nephridio- pores, and four behind the one bearing the last pair, giving a total of 26 true segments, of which each of the first six and the last four has Jess than five annuli. (b) The anterior sucker, oval in shape, at the anterior end of the body. It has a cup-like hollow, in the middle of which is a small aperture, the mouth, with the three jaws surrounding it. (c) The blind posterior sucker, at the posterior end of the body, circular in shape and larger than the anterior one. (d) The male genital aperture, situated in the middle of the second annulus of the 10th segment. (e) The female genital aperture, situated in the middle of the second annulus of the 11th segment. 2. Make a drawing of the dorsal surface of the first seven segments to show : (a) The five pairs of small eyes on the dorsal surface of the anterior sucker. (b) The sensory papille, six in the anterior annulus of each segment, except in those annuli containing the eyes. Here there are only four, the eyes taking the place of the other two in annuli 1, 2,3,5 and 8. There are five pairs of eyes. 3. Make a drawing of the dorsal surface of the last four segments to show : (a) The anus, situated in the middle of the last annulus of the body, just in front of the junction between the posterior sucker and the end of the body. (b) The sensory papille, occupying the same positions as in the other segments. General Structure. Pin the animal down under water, with the dorsal surface uppermost, by inserting pins through the sides of the suckers. Cut along the mid-dorsal line, 64 66 THE MEDICINAL LEECH taking care not to injure the alimentary canal, which lies close to the skin. Carefully remove the integument from the alimentary canal and pin out the flaps on each side. Note the dorsal blood-vessel lying over the alimentary canal in the mid-dorsal line. Note the nephridia, a pair occurring in each segment from the 6th to the 22nd. Each nephridium has a closed but porous funnel, the “ testis-lobe,” contained in a cavity of the ccelom above the testis, a much-coiled glandular main portion with fine ciliated ducts and blood capillaries in its walls, and a muscular ciliated bladder opening to the exterior by a nephridiopore. The inner end of the ““testis-lobe ’’ probably corresponds to the nephrostome of the Earth-worm. A, The Alimentary System. The mouth is situated in the anterior sucker and is surrounded by the jaws. These are arranged radially, one being median and dorsal, the other two ventro- lateral. Each is a compressed muscular cushion with a chitinous surface pro- duced into numerous teeth. The mouth leads into a muscular pharynx situated in the 4th to 7th segments. It is connected by strong radiating muscles to the body-wall. There are numerous unicellular glands in the wall of the pharynx, and the secretion of these glands prevents the coagulation of the blood. The cesophagus, following the pharynx, is a very short tube leading into the exten- sive crop. This consists of eleven pouches on each side, the first ten pairs of these storing pockets being directed outwards and each corresponding to a segment. The eleventh pair passes backwards parallel to the intestine and reaches to the 24th segment. After giving off the eleventh pair the crop is succeeded by the stomach, a small spherical dilatation, opening behind into the intestine, a narrow straight tube passing into the somewhat dilated rectum, which turns slightly upwards and opens at the anus in the last annulus of the last segment. B. The Vascular System. This system is complex. It consists of a spongework of sinuses (i.¢., irregular channels with non-muscular walls) filled with a fluid which is not really blood, but which apparently functions as such, namely, ccelomic fluid containing the red blood-pigment, hemoglobin. The spongework completely fills the original open space, the body-cavity or coelome, which is consequently represented by the complicated system of coelomic sinuses, and these seemingly replace the true blood-vessels of a proper blood system. The principal sinuses are : (a) The dorsal sinus, along the mid-dorsal line above the alimentary canal, and connected behind with the ventral sinus by fine channels which pass between the intestine and the last pair of storing pockets. (b) The ventral sinus, under the alimentary canal. It surrounds and en- closes the ventral nerve cord. (c) The lateral ‘‘ blood-vessels,”’ a pair of tubular channels along the sides of the body. These are probably sinuses with muscular walls. They are connected by cross channels, which pass beneath the ventral sinus. Make a drawing showing as much as possible of the alimentary system and the vascular system. 68 THE MEDICINAL LEECH C. The Nervous System. Cut through the anterior end of the pharynx and remove the alimentary canal from:the body. On the anterior part of the pharynx are the two supra- pharyngeal ganglia. They are connected by the circum-pharyngeal com- missures to the ventral nerve-chain, which lies inside the ventral sinus and which consists of twenty-three pairs of ganglia connected by two very closely Mouth a Anterior sucker ie . Supra-pharyngeal ganglia -- Ist ganglion Eyés »- Jaw"” é a Sensory papilla a ist nephridium hee {st diverticulum ) # “B of crop./-. --- Ductus - ejaculatorius far -" Male genital x _, aperture Female genital M “"pertere - Penis i “Vesicuta Ovarye~ seminalis x oe Yagina --4- Ist cestis ‘ii . Si - Ner rd . Bladder Nephrostome Rega Nes iv cy -- Nephridioporg eehsk % -}*Lateral vessel %y a D Vas deferens xv eee oO “-* Sensory papilla ae xvy ** Oviduct -{-Vasa efferentia xv - Common duct ahaa Stomach-}----{- Vagina. llth diverticulum crop- -\---> ~ 17th nephridium -*Rectum 23rd inate -—* Anus ~ ” Posterior sucker Fic. 22,—A. The Leech (Hirudo medicinalis), ventral view; B. Dorsal view of anterior segments; C. Dorsal view of posterior segments; D. Nephridium; E. Female genital organs (spread out); F. Dissection (made from dorsal: surface) to show the internal structure. The alimentary canal has been cut open and the right half removed (as far as the end of the crop), so as to expose the underlying organs. A.—E., after Borradaile ; F., after Parker and Haswell. apposed connectives. The first or sub-pharyngeal ganglia are larger than .the others and represent the fusion of the first five pairs of ganglia. The last ganglia represent six or seven pairs fused together. Each ganglion or conjoint pair of ganglia gives off nerves to suED hy the corresponding segment. D. Reproductive System. The ovaries are a pair of very small coiled bodies enclosed in small rounded sacs, lying close to the mid-ventral line in the 11th segment. From each: sac a short oviduct passes inwards and backwards; the right one passes under 70 THE MEDICINAL LEECH the nerve cord and unites with the left one to form a common median duct. This common duct is surrounded by the albumen gland, and it opens into a curved muscular tube, the vagina, which opens in the middle line on the ventral surface of the second annulus of the 11th segment. The testes are nine pairs of spherical sacs lying along each side of the ventral sinus in segments 12-20. Each gives off from its outer surface a narrow efferent duct, which joins the larger vas deferens running parallel to the alimentary canal. In the 10th segment each vas deferens increases in width and forms a complex coil, the epididymis or vesicula seminalis, giving rise anteriorly to a widened muscular tube, the ductus ejaculatorius. From each ductus ejaculatorius a narrow duct passes to the penis, which is a curved muscular organ protrusible through the male genital aperture in the middle line on the ventral surface of the second annulus of the 10th segment. Make a drawing to show the Nervous System and the Reproductive System. Fic, 23.—Transverse Section (diagrammatic) through the middle of the body of the Leech (Hirudo). A nephridium is shown (entire) on the left side of the figure. After Marshall and Hurst. With permission from Parker and Haswell’s T'ezxt-book of Zoology. cu. cuticle; d.ep, epidermis; c.m. circular and oblique muscles ; l,m. longitudinal muscles; d.v.m. dorso- ventral muscles; b.t, botryoidal tissue; er. crop; er/. diverticula of crop (storing pockets); d,s. dorsal sinus; /.y. lateral sinus or ‘‘ blood-vessel”; v8, ventral sinus; #.¢. nerve cord; 7.8. nephrostomial sinus; ts, testis; v.d. vas deferens; nph. section of nephridium; nph, 1. anterior limb of main lobe of nephridium ; nph. 2. posterior limb of main lobe of nephridium; nph. 3, apical lobe of nephridium ; nph. h, testis-lobe of nephridium ; nst. ‘‘cauliflower lobe" or inner end of the testis-lobe (nephrostome) ; vs. vesicle or bladder of nephridium ; xp. external aperture of nephridium or nephridiopore. Transverse Section of Body. In a transverse section of the body of a Leech the following structures may be seen :—- (a) The thin cuticle. (b) The epidermis. THE MEDICINAL LEECH (c) The dermis, containing a plexus of ‘“ blood ” capillaries. (d) The circular and oblique muscles. (e) The longitudinal muscles. (f) The dorso-ventral muscles, passing from the dermis through the circular muscles and between the longitudinal muscles. (g) The botryoidal tissue around the crop and occupying most of the body cavity or coelome. (h) The crop, with its lateral pouches or storing pockets. (t) The lateral “‘ blood-vessels ” or sinuses on the outer side of the crop. (j) The dorsal sinus above the crop. (k) The ventral sinus surrounding and enclosing the nerve cord. (1) The peri-nephrostomial sinuses above the testis and enclosing the “testis-lobe ” of the nephridium. (m) The vas deferens between the lateral sinus and the ventral sinus. (n) Portions of the nephridia. THE COCKROACH (Periplaneta americana) External Features. 1. Make a drawing of : (i) A dorsal view of the Cockroach with the wings of the right side extended showing : (a) The head, bearing the eyes and the antenne. (b) The prothorax, to the underside of which the first pair of walk- ing legs is attached. The dorsal shield of the prothorax, the pronotum, is large and projects forwards, so that it conceals the short and thin neck; and the head may also be drawn under it. (c) The mesothorax, to the under side of which the second pair of walking legs is attached. The anterior wings are dark coloured ; they protect the posterior wings, and are known as the wing-covers or elytra or tegmina. They are attached to the dorsal surface. Note that the wing-covers extend beyond the posterior end of the body. The dorsal shield of the mesothorax, the mesonotum, is thin and semi-transparent, being covered by the wing-covers. (d) The metathorax, bearing the third pair of walking legs on its ventral surface and the posterior pair of wings on the dorsal surface. The metanotum or dorsal shield of the metathorax is smaller than, but similar to, the mesonotum. (e) The abdomen. In both sexes there are ten abdominal segments, but in the female some of the segments are modified. A typical abdominal segment has a broad dorsal chitinous plate, the tergum, and an equally broad ventral plate, the sternum. The tergum and sternum meet at an acute angle at the sides of the body, and are united by a soft colourless cuticle. In the abdomen of the female cockroach only eight terga are externally visible. These are the first seven and the 10th. Two more (8th and 9th) are usually concealed beneath the 7th tergum, but they may be seen by extending the abdomen. The 10th tergum is a flat plate notched in the middle of its posterior margin. Beneath it are two triangular chitinous sclerites, the podical plates, between which the anus opens in the middle line. The abdomen of the female is broader and flatter than that of the male. In the male the abdomen is narrower and the terga more con- vex than in thefemale. The first tergum is somewhat small and the sternum is only an oval chitinous plate. Both the terga and sterna of the next six segments are broad chitinous plates ; 74 76 THE COCKROACH put the 8th and 9th terga are reduced to narrow bands of chitin, overlapped and concealed by the posterior margin of the 7th tergum as in the female. The 10th tergum is a flat rounded plate, projecting beyond the posterior margin of the Fic. 24.—The Cockroach (Periplaneta americana). Male (x 14). body, with a notch in its posterior margin. Under it lie the podical plates and the anus as in the female. The anal cerci, occurring in both sexes, are a pair of spindle- shaped, many-jointed appendages projecting beneath the edge of the 10th tergum. The anal styles, occurring in the male only, are attached to the sternum of the 9th segment. (See Fig. 27, A.) (ii) A ventral view showing the position of the head with its appendages, and also the attachments of the legs as described above, the anal cerci (and styles in the male) and the opening of the anus. Notice the stigmata or respiratory openings (twenty pairs) on the sides of the body, between the thoracic segments and on the first eight abdominal segments (between the tergum and sternum, and at the front end of each segment). 78 THE COCKROACH The Head. The head, as seen from the front, is pear-shaped, having a semicircular outline above and narrowing downwards. A side view shows that it is com- pressed from front to back, with top and sides regularly rounded. The mouth, surrounded by the jaws, opens below. The clypeus occupies the large central part of the front, and extends almost completely across the widest part of the face. It is divided above by a sharply bent suture from the two epicranial plates, which form the top of the head as well as a great part of its back and sides. The labrum or upper lip hangs like a flap from its lower edge. A little Epicranial plate ay “Dorsal sclerite Epicranial suture Fenestra -“,Epicranial plate cs “7k Fic. 25.—The Cockroach (Periplaneta americana). A. Front view ; B. Side view ; C. Dorsal view of the head. above the articulation of the labrum the width of the clypeus is reduced. In the angle so formed the anterior articulation of the mandible is situated. The labrum is narrower than the clypeus and of a square shape, the lower angles being rounded. It hangs down and forms the front wall of the mouth. The top and back of the head are covered by two epicranial plates, which meet in the middle line. The sides of the head are completed by the eyes and the gens or “cheeks.” The large compound eye is bounded above by the epicranium, and in front, by a narrow band which connects the epicranium with the clypeus, and behind, by the gena. The gena passes downwards between the eye and the epicranial plate, then curves beneath the eye, and just appears upon the front of the face, being loosely connected at this point with the clypeus. A shield-shaped aperture on the posterior surface of the head, called the occipital foramen, marks the place where the neck joins the back of the head. The neck itself is slender and soft, and is covered with a soft white cuticle, except 80 THE COCKROACH where the eight hard chitinous plates or sclerites occur, there being two dorsal, two ventral, and two lateral pairs of these plates. The antennz are attached to the front of the head immediately below the eyes. Each antenna consists of a stout basal joint, movably articulated, by a ring of soft cuticle, in a cavity of the clypeus. On the inner and upper side of each antenna is a small circular white area, situated at the end of the suture dividing the epicranium from the clypeus. These areas are called the fenestre. Make three drawings of the head to show (i) the front, (ii) the side, and (iii) the dorsal aspect. - f-~Maxillary palp SECOND MAXILL® FIRST MAXILLA (LABIUM) (OF LEFT SIDE) Fic. 26.—Appendages of the Cockroach (Periplaneta americana). The part of the second maxilla marked L is the glossa, which corresponds to the lacinia of the first maxilla. The Mouth Parts. Remove the labrum so as to expose the mandibles. Each mandible is attached by a convex condyle to the lower end of the epicranial plate, and also by a concave anterior articulation to the clypeus. Remove and draw a mandible, noting the strong tooth-like process of chitin. Situated just behind the mandible of either side is the 1st maxilla. Remove and draw the 1st maxilla, noting its parts :—A basal two-jointed portion con- sisting of the cardo and the stipes. The cardo is a transverse plate bent upon itself and bearing the stipes. To the side and lower end of the stipes is attached the five-jointed maxillary palp, while the lacinia and galea are articulated to its extremity. The lacinia is internal and posterior to the galea. Its base is broad and it narrows to a bifid tooth of hard chitin. Its inner surface is beset with a cluster of strong sete. On the posterior surface of the head, below the occipital foramen, the lower lip or labium is situated. It is formed by the fusion of the basal portions of the 82 THE COCKROACH second maxillz. It is continuous with the chitinous integument of the neck. Remove and draw the labium, noting its parts :—’The broad shield-like base divided by a transverse suture into a large submentum (the fused cardines), and a distal smaller mentum (the fused stipites). To the mentum are attached the free portions of the second maxilla, each consisting of the paraglossa corresponding to the galea, the glossa corresponding to the lacinia, and the three-jointed labial palp. The paraglosse and glossz together constitute the ligula. A Walking Leg. Remove and draw the metathoracic leg of the left side, noting its parts :— (a) The coxa, the broad and flattened basal portion. (b) The trochanter, a small piece obliquely and almost immovably attached to the proximal end of the femur, on its inner side. (c) The femur, nearly straight and narrowed at both ends, and with a shallow longitudinal groove, fringed by stiff bristles, ‘along its inner border. (d) The tibia, longer than the femur, and armed with numerous stiff spines directed towards the free end of the limb. (e) The five-jointed tarsus, the proximal joint being the longest, while the distal joint, the pulvillus, bears a pair of equal and strongly curved claws. Internal Structure. A. The Alimentary System, and associated organs. Cut through the junction of the terga and sterna of the abdomen and the thorax, and completely remove the terga, taking care not to injure the under- lying structures. Notice the tubular and chambered heart along the middle line of the body, the diffuse white fatty body, and the silvery air-tubes or trachee. Carefully free the alimentary canal from the fatty body and the trachez which envelop it, and examine and draw the following parts :— The mouth opens into the buccal cavity, on the floor of which is a raised fold, the lingua or tongue or hypopharynx. The ducts from a pair of salivary glands with reservoirs open into the buccal cavity, which is continued into the ceso- phagus. The cesophagus is a very narrow tube, laterally compressed in the neck, but in the thorax it gradually expands into the very long and thin-walled crop, which extends back into the abdomen. The crop is followed by a short conical gizzard or proventriculus, with thick muscular walls, and containing six teeth and six pads with sete. These aforenamed parts are lined with cuticle and represent the fore-gut or stomodeum. The narrow end of the gizzard leads into the stomach (the mid-gut or mesenteron). The stomach is a simple tube, provided, at its anterior end, with eight hepatic ceca which secrete a digestive fluid ; and, at its posterior end, there are six bundles of very fine and long Malpighian tubules, which are the excretory organs. Each bundle comprises ten or more thread-like tubules, so that as many as sixty to seventy tubules may be present. The stomach then leads into the small intestine or ileum, which is followed by the large intestine, represented by the colon and the short rectum, 84 THE COCKROACH which has six long rectal bands on its surface. The ileum, colon and rectum represent the hind-gut or proctodeum. The anus opens beneath the 10th tergum and between the podical plates. B. The Nervous System. Remove the epicranial plates of the head so as to expose the brain, which Cerebral ganglia wk i Optic nerve ~Antennary nerve \Y¥ “-Suboesophageal ganglion Ne ety T ganglion : EB rg NU Mesothoracic i ye i “Y © ganglion ee Wy Muscles ~-..----~7 é Ss Y_-Metathoracic ~~ F WS ganglion’ _--- Salivary gland RS eR A e AAR x S Dy “Salivary reservoir ceca ‘4 .-Stomach Malpighian / tubules --6th Abdominal Rectum Fic. 27.—The Cockroach (Periplaneta americana). A. Dissection of male showing the’alimentary system, etc. ; B. Nervous system. consists of two supra-cesophageal or cerebral ganglia incompletely divided by a deep and narrow median fissure. The optic and antennary nerves are given off to the eyes and the antennz respectively. The cerebral ganglia are connected by the circum-cesophageal commissures to the sub-cesophageal ganglia lying in the head immediately in front of the submentum. The sub-cesophageal ganglia supply nerves to the mandibles, maxilla, and labium, and are joined by a long and 86 THE COCKROACH slender pair of connectives (arising from the top of the ganglia) with the first pair of thoracic ganglia lying in the pro-thorax. There is a pair of ganglia in each of the thoracic segments and in each of the first six abdominal segments. A double ventral nerve-chain connects the ganglia; each pair supplies its own segment with nerves, while the sixth abdominal ganglion supplies its own segment and also the posterior segments of the body. Make a drawing of the nervous system. THE FRESH-WATER CRAYFISH (Astacus) THE CAPE CRAWFISH (Jasus lalandii) First Day External Features. 1. Make a drawing of the animal viewed from the dorsal surface to show : (a) The large carapace or cephalo-thoracic shield covering the whole of the head region and thorax. The carapace is marked off by grooves into definite areas, which may be named after the organs in the body over which they lie. There is a short transverse groove in the middle of the carapace called the cervical or neck groove, which marks off the head region from the thorax. The part of the carapace, in front of this groove covers the stomach, and may therefore be called (i) the cephalo-gastric region. The part just behind this covers the heart, and may be called (ii) the cardiac or thoracic region. On each side of the body there is a part of the carapace which protects the gills ; these gill-covers are called the branchiostegites, and form (iii) the branchial region of the carapace. The grooves which mark them off from the cardiac region are called the branchio-cardiac grooves. If these grooves are traced forwards it will be seen that each divides into two branches, one passing forward towards the base of the antenna and the other and more distinct one passing to the underside of the body. These two branches enclose a small area of the carapace covering the liver and which is therefore called (iv) the hepatic region. On the cephalo-gastric region a prominent projection of the carapace in the middle line is seen; this is the rostrum. It has a broad base and ends in front in a sharp spine. It has a smaller spine on each side. [In Jasus the rostrum is small.] (b) The six abdominal segments, at the end of which is the telson which may represent the 7th abdominal segment. Each has a ring-like form, presenting a broad dorsal region or tergum, a narrow ventral region or sternum, and downwardly directed lateral processes, the pleura. (c) The stalked eyes, situated at the anterior end of the cephalo-thorax, one on either side of the rostrum. (a) The following appendages as seen from above :—- (i) The pair of biramous antennules, each with an otocyst, the auditory and balancing organ, on their basal joints. [In Jasus the antennules have each a pair of small terminal flagella. | (ii) The pair of antenne. (iii) The five pairs of walking legs. The anterior three walking legs of each side end in a pincer-like claw. The first walking leg (the cheliped) is much stouter than any of the others, its claw 88 90 THE FRESH-WATER CRAYFISH—THE CAPE CRAWFISH being very large. [In Jasus this claw is absent, but in the female the posterior walking leg of each side bears a small claw or chela. | (iv) The large fan-shaped appendages or uropods of the 6th ab- dominal segment which, together with the telson, form the tail. Fic. 28.—The European Fresh-water Crayfish (A stacus). 2. Examine the specimen from the ventral surface and note :— (a) The opening of the “green gland” or nephridium at the base of each antenna. (6) The appendages of the head and the first three pairs of thoracic append- ages crowded together. 92 THE FRESH-WATER CRAYFISH—THE CAPE CRAWFISH (c) The five pairs of walking legs. In the male there-is a genital aperture at the base of the fifth leg of each side. In the female the genital apertures occur at the bases of the third legs. ul : Fic. 29.—The Cape Crawfish or Kreeft (Jasus lalandii). Greatly reduced. (d) The appendages of the abdomen. These are attached to the hinder side of the sternum near its outer ends, and the part of the sternum between each appendage and the adjoining pleuron is called an epimeron. 94 THE FRESH-WATER CRAYFISH—THE CAPE CRAWFISH (e) The telson. (f) The anus, situated on the ventral surface of the telson. The Respiratory System. Cut along the branchio-cardiac groove of the left side with a pair of scissors, and remove the branchiostegite so as to expose the branchial chamber with the gills. The gills are soft and feathery vascular outgrowths. The stem of each gill contains two longitudinal vessels (afferent and efferent), with which the numerous hollow thin-walled filaments are connected. The gills receive differ ent names according to their positions, and are thus divided into three sets : (a) The podobranchs, attached with the epipodites to the basal segment of each thoracic appendage except the first maxillipedes and the fifth walking legs. The epipodites are thin leaf-like plates directed up- wards and lying in the gill cavity between the thoracic wall and the branchiostegite. (b) The arthrobranchs, attached to the membrane connecting the thoracic appendages with the trunk. They are usually in pairs, and are separ- ated from the podobranchs by the epipodites. (c) The pleurobranchs, attached to the inner wall of the branchial chamber above the attachments of the appendages. The number and arrangement of the gills in Astacus is as follows :— Appendage Podobranch | Arthrobranch Pleurobranch Second maxilla . é : 3 0 0 0 First maxilliped “ 5 . ep 0 0 Second maxilliped . " ‘ l+ep 1 0 Third maxilliped ‘ é l+ep 2 0 First walking leg or cheliped ‘ l+ep 2 0 Second walking leg ,, . 3 l+ep 2 0 (1) Third walking leg. 5 ‘ l+ep 2 r (1) Fourth ne ie : 5 l+ep 2 r (1) Fifth walking leg . 0 0 1 Total 6 1l 14 2r (4) ( ep, signifies an epipodite. r, signifies a rudimentary gill. The figures in brackets show the differences in the gill formula between Astacus and Jasus, which has four pleurobranchs. N.B.--The Norway lobster (Nephrops) has five podobranchs and a rudiment (on second maxilliped), eleven arthrobranchs, and four pleurobranchs. The Appendages. Remove the appendages from the left side of the animal, commencing with the uropods and working forwards to the head. Lay them out in the order in which they were removed :— A. The Five Abdominal Appendages of the Left Side. There are appendages on all the abdominal segments except the telson. [In. Jasus there are no appendages on the first and the last segments. . - A GX _ “(snovjsy) ysykerp 10yem-ysorg 044 Jo sesepueddy—-og OLT qogoun ‘Ax aupodoiosg. A aa OgadITTIXVW PIE TIA Gad THUXVW 31 TA \ onpodidg-- ayypodoxg, - .- --opodopug --pypodoxoy anpodoxy- VTTIXVYW PO A (@yewIy) GOdOATd PAE ATK (@pEW) > dOdOA ld Pte “IX aupodoxos ; sypodoxoy- VTIEXVWW 3ST “AL <" BiIpodiseg @upodiseg-- agppEUsougdeog - fe cf « onpodoxg-4 oupodoxa& /eupodopug BE # -onpodoxop nd ye @rA) -oupodopug \ , GOdOdTd PU “TIX (arew) &--d1Tpodiseg doOd0a Td 31 *X ’ 2 3 a a aiypodopuy-" Inner 96 THE FRESH-WATER CRAYFISH—THE CAPE CRAWFISH * uropod consists of a basal segment or protopodite, which is very broad (a) The uropod is attached to the side of the 6th abdominal segment. ee YB: k-onpodopug } y aupodoyéiosg (ajema7) 'GOdOF'Td 31 1X -eurpodoxop THD. -aupodidg eupodoj 28g a GadITUXVW PUZ ILA @podoryy Peih aypodopuy = XTSIGNVW ‘MIT ooo puy[s waar) yo Buraadg FINNNGLNV 1 VNN@LNV ‘I “sanpodoioig .--2 20d S a1ped 010s." fled . -anpodopuyq aypodoxg. aupodopug and thick and not divided into two joints, and which bears a broad flattened outer branch or exopodite, and a similarly shaped 98 THE FRESH-WATER CRAYFISH—THE CAPE CRAWFISH branch or endopodite. The two uropods, together with the median telson, form the five-lobed tail, the swimming paddle. (b) The pleopods are attached on each side of the Ist to 5th segments. In the female the first pleopod is more or less vestigial. In the male the first and second pleopods form incomplete tubes and act as copulatory organs. The coxopodite is present, but there is no exopodite and the basipodite appears fused with the endopodite. A typical pleopod—-e.g., the second—consists of a basal segment or protopodite, composed of coxopodite and basipodite, bearing an endopodite whose proximal joint is enlarged and an exopodite in the form of a jointed rod. [In Jasus the pleopods are atiached to the second, third, fourth, and fifth seg- ments. In the female the first pleopod is composed of a single basal protopodite bearing an endopodite and an exopodite which are equally developed. The second, third, and fourth have the endopodite in the form of a rod. In the male the endo- podite is absent, all the pleopods being similar. | Draw a uropod, and the first and third pleopods. B. The Hight Thoracic Appendages of the Left Side. These are divided into the five walking legs and the three maxillipeds. (a) The walking legs or pereiopods are attached to the side of the thoracic region. Each leg is composed of a basal two-jointed protopodite (the coxopodite and the basipodite) and a five-jointed endopodite (the ischiopodite, meropodite, carpopodite, propodite, and dactylopodite). There is no exopodite. A podo- branch and an epipodite are attached to the coxopodite of the first four walking legs of each side. The first pereiopod of each side ends in a large pincer-like claw or chela, formed by the dactylopodite working against a prolongation of the propodite, and is therefore called the cheliped. In the second and third pereiopods of each side there is also a claw present, _ but it is much smaller than that of the first walking leg. Note the genital apertures. [In Jasus the chela is usually present on the last pair of pereiopods in the female. ] (b) The Maxillipeds. (i) The third maxilliped is attached just anterior to the first walking leg. It is composed of a basal two-jointed protopodite (the coxopodite and the basipodite) bearing a five-jointed endopodite (the ischio- podite, meropodite, carpopodite, propodite, and dactylopodite) and a smaller exopodite ending in a feeler-like flagellum. A podobranch and an epipodite are attached to the coxopodite. (ii) The second maxilliped resembles the third, but is smaller. [In Jasus the endopodite is only four-jointed, the ischiopodite and meropodite having fused together. | : (iii) The first maxilliped differs from the other two. The coxopodite and basipodite are broad thin plates, while the endopodite is short and only two-jointed. The unjointed portion of the exopodite is long. An epipodite is present, but it has no gill. [In Jasus the endopodite is only single-jointed. | 100 THE FRESH-WATER CRAYFISH—THE CAPE CRAWFISH Draw the third and first walking legs, and the third, second, and first maxillipeds. .Endopodite _Exopodite XIV. UROPOD =>, Endopodite Exopodite _.., Protopadite XII. 3rd PLEOPOD Exopodite : XE Sth PEREIOPOD Endopodite XI Ist PLEOPOD Protopodite Protopodite Epipodite »», Dactylopodite \Propadite Reduced. ““"“Endopodite topodite Dactylopodite -~.__-F% : -~--Carpopadite Pro A, _-ischapodite Basipodite A _- Ischiapodite VU. 3rd MAXILLIPED WH NUR rcamen canna eter : A RASS STU ATS URCCSMLLCA US ‘ X. 3rd PEREIOPOD ; Fic. 31.—Appendages of the Cape Crawfish (Jasus). : i i i 2 -& 3 i 4 ee 3 g 6 O68 I zg Sap 2 5. z a” Aer fai, E a ‘ i Bo ig 2 22 3 i se z o eo (ie § $3 3 a eB z z 8 kG 55 NL, 3 i —f Avy } fae 2 2 3 ‘ Z = : 2 é C. The Five Head Appendages of the Left Side. These are modified chiefly into sensory and oral organs. (a) The second maxilla is situated in front of the first maxilliped but towards the side of the body. The protopodite consists of two thin lamellar plates (coxopodite and basipodite) subdivided by deep fissures. The 102 THE FRESH-WATER CRAYFISH—THE CAPE CRAWFISH endopodite is very small, and the exopodite is fused with the epi- podite to form the scaphognathite or baler. The function of the baler is respiratory ; it causes a constant forward current of water in the gill chamber. [In Jasus the protopodite has three pointed prolongations and is very small. | (b) The first maxilla consists of three leaf-like parts, the basal two being the protopodite, while the single distal one is the endopodite. The exopodite is absent. (c) The mandible consists of a strong and transversely elongated proto- podite, bearing a three-jointed palp, which is the endopodite. [In Jasus the basal joint of the palp is regarded as the protopodite, and the remaining joints as the endopodite. ] (d) The antenna has a two-jointed protopodite. The basal joint is small, and on its ventral face is the opening of the “ green gland.” The upper joint is larger and externally it bears a broad flat exopodite or squame, while internally the feeler, the elongated endopodite, is attached to it by two stout basal joints. [In Jasus there is no exopodite, and the basal joint of the protopodite is fused to the body. | (e) The antennule has a three-jointed base (the protopodite) and two terminal flagella representing the exopodite and the endopodite. [In Jasus the protopodite is two-jointed, the endopodite is a single two-jointed rod terminating in two small flagella, and the exopodite is absent.| Draw the above appendages. Second Day Internal Structure. Cut along the branchio-cardiac groove of each side with a pair of scissors from behind forwards and remove the branchiostegites of each side. Carefully raise the central part of the carapace from behind, separate it from the under- lying integument, and then remove it completely by severing it just behind the rostrum. Cut through the tergal or dorsal portions of the abdominal segments on both sides and remove them. Remove the brightly pigmented tissue which lines the inside of the carapace, so as to expose the internal organs. Note the following structures :—- (a) The dorsal extensor muscles, paired longitudinal bands along the dorsal region of the abdomen and inserted into the front of each segment. (b) The large abdominal flexor muscles, occupying the ventral region of the abdomen, and arising from the endophragmal skeleton. (ce) The dorsal extensor muscles, arising from the sides of the thorax. (d) The “stomach” or gizzard, situated in the anterior region of the cephalo-thorax. Notice the two pairs of muscles, arising from the body-wall, which work the gizzard. (e) The adductor muscles, working the mandibles, situated on either side of the posterior end of the gizzard. 104 THE FRESH-WATER CRAYFISH—THE CAPE CRAWFISH (f) The digestive glands or “liver.” a yellowish bilobed mass of coiled tubes, lying in the thorax on each side of the alimentary canal. (g) The long and straight intestine, along the mid-dorsal line of the body, and between the extensor and flexor muscles in the abdomen. (h) The gonad (testis in male or ovary in the female), portions of it on each side of the intestine. Note the long and coiled vasa deferentia (or short oviducts in the female). (7) The heart lying within the pericardium in the dorsal region of the thorax. (j) The median ophthalmic, antennary, hepatic, and superior abdominal arteries. A. The Vascular System (part). Examine the heart and note that it has three pairs of apertures or ostia— a pair on the dorsal surface, a pair on the ventral surface, and a pair placed laterally. [In Jasus there are two pairs of ostia placed dorsally.| The heart is attached to the walls of the pericardial sinus or pericardium by strands of con- nective tissue. From the anterior end of the heart the following vessels arise :— (a) The single median ophthalmic artery, which passes over the gizzard and then branches into two ophthalmic arteries, one to each eye. (b) The pair of antennary arteries, one passing over the “liver”? on each side and supplying the antennz. (c) The pair of hepatic arteries arising one on either side of the heart between the ophthalmic and antennary artery, and passing down into the substance of the “ livér.” From the posterior end of the heart there arises the superior abdominal artery, which passes backwards on the dorsal surface of the intestine to the tail region. It supplies each segment of the abdomen by a pair of smaller arteries. Just posterior to the heart the superior abdominal artery gives rise to a sternal artery, which passes vertically downwards to the ventral region of the cephalo- thorax. Sever this artery at its origin, and lay it aside for further examination. B. The Alimentary System. The mouth is an elongated opening below the head. It is bounded in front by a wide upper lip or labrum, on the sides by the mandibles, and behind by the paragnatha, which resembles the first maxilla. A short wide gullet leads up- wards and forwards from the mouth to the large stomach or gizzard, which is divided into two portions, the anterior cardiac chamber or gastric mill and the smaller posterior pyloric chamber. From this the short mid-gut or mesenteron, which has a dorsal pouch or cecum, leads into the long intestine, which ends at the anus situated beneath the telson. The gullet and gizzard represent the fore-gut or stomodzum ; and the intestine is the hind-gut or proctodeum. Note the large “‘liver,”’ which consists of two digestive glands, a big yellow- ish mass of tubules, lying on each side of the pyloric stomach. Ducts from the tubules unite into an hepatic duct opening into the mesenteron on each side. Cut through the gullet or cesophagus and the intestine (near the anus), and carefully remove the alimentary canal with the attached “‘liver.”” Remove the ‘liver ”’ on the left side, and make a side-view sketch of the alimentary canal. Remove the stomach or gizzard and open it along the ventral wall. Note 106 THE FRESH-WATER CRAYFISH—THE CAPE CRAWFISH the internal structure. The gastric mill contains ossicles and teeth, and in the pyloric portion there is a sieve of fine hairs. C. The Reproductive System. In the Female note :— - (a) The ovary (when ripe) is a Y-shaped organ, consisting of two anterior lobes and a posterior lobe. [In Jasus the ovaries are a pair of long reddish organs, lying on either side of the alimentary canal, and united by a median transverse bridge. | (b) The oviducts, a pair of short straight tubes, one leading from each lobe to open at the genital aperture on the third walking leg. In the Male note :— (a) The testis, which is three-lobed, like the ovary, and similarly situated. [In Jasus the testes are a pair of elongate white organs, connected together like the ovaries, and in a similar position.) — (b) The vasa deferentia, a pair of thick, coiled, white tubes, each given off at the junction of the three lobes, and opening to the exterior at the genital aperture on the last walking leg. Make a complete drawing showing the vascular, alimentary, reproductive and muscular systems. Remove, and draw, the gonad (male or female) with its ducts. D. The Skeletal System. Remove all the muscles from the cephalo-thorax and the abdomen so as to expose the internal skeleton, taking care not to break the sternal artery. The ventral and lateral regions of the thoracic exoskeleton are produced into the interior of the body in the form of a segmental series of calcified plates, so arranged as to form a row of lateral chambers in which lie the muscles of the limbs, and a median tunnel-like passage or sternal canal, containing the thoracic portion of the nervous system. This entire endophragmal system, as the series of plates is called, constitutes a kind of internal skeleton. E. The Nervous System. Expose the nerve cord in the abdominal region and trace it forwards. In this region note the six abdominal ganglia on the nerve cord. The sixth ganglion is the largest and represents the ganglion of the 6th abdominal seg- ment and that of the telson fused together. The pairs of ganglia are fused, and the double nerve cord is fused in the abdominal region. In the cephalothorax the paired nerve cord lies in the sternal canal of the endophragmal skeleton. In order to expose it, cut through the sternal canal on each side and remove the roof. Note the sub-cesophageal ganglion, a fused mass consisting of the three posterior cephalic and the three anterior thoracic ganglia. Leading from the sub- cesophageal ganglion, on each side of the cesophagus, is the circum-cesophageal commissure connecting it with the supra-cesophageal ganglion situated at the base of the antennules. This ganglion sends nerves to the eyes, antennules and antennz. The sub-cesophageal ganglion supplies the mandibles, maxille, and the first and second maxillipeds. In each remaining segment of the cephalo- thorax is an indistinctly-double ganglion sending nerves to the third maxillipeds 108 THE FRESH-WATER CRAYFISH—THE CAPE CRAWFISH and the walking legs. The ganglia are connected by a double nerve cord. There are six pairs of free thoracic ganglia, each pair being incompletely fused. Between the fourth and fifth thoracic ganglia the double nerve cord is separated to form a loop through which the sternal artery passes. Optic nerve Cerebral ganglion-- -- Anterior visceral nerve --Adductor muscle i --Stomach of Mandible Se esac Ophthalmic aEteey ~ Suboesophageal --Digestive gland ganglion -Antennary artery ~1Ist Thoracic ganglion -Hepatic artery --Testis -Ostium --Heart oth Thoracic ganglion- ~Vas deferens - Loop for Sternal artery “Endophragmal skeleton :+Flexor muscles o ti. Intestine of Abdomen - i ei fS --dntestine ase - Superior abdominal artery --Posterior visceral nerve 5S > ” Fia. 32. —The Fresh-water Crayfish (As/acus). A. Dissection of a male showing the general structure ; B. the nervous system. Note the transverse post-cesophageal commissure immediately behind the cesophagus and joining the two circum-cesophageal commissures. From the supra-cesophageal ganglion a visceral nerve passes backwards to supply the stomach, while from the last abdominal ganglion there arises a posterior visceral nerve supplying the intestine. [In Jasus there are five pairs of free thoracic ganglia, and the loop for the sternal artery occurs between the third and fourth pairs. | 110 THE FRESH-WATER CRAYFISH—THE CAPE CRAWFISH F. The Vascular System (continued). Trace the sternal artery through the aperture in the nerve cord ; and note that it divides ventrally into the ventral thoracic artery and the inferior Cerebral ganglia--.._ _. Stomach y . : -Circumcesophageal Visceral nerve- Pee Adductor muscle of Mandible Ophthalmic { ££ A\ -fa-\------ Postoesophageal artery. commissure BALK Hepatic ANY ay artery Subcesophageal AY NWN NY Pee ay ganglion . Heart Ist Thoracic - Testis ganglion --Loop for Sternal artery 5th Thoracic ganglion -- Sternal artery ~Extensor muscles -- Vas deferens Intestine Endophragmal! skeleton‘ -Sternal canal ; r Ist Abdominal Superior abdominal ganglion artery Flexor muscles Visceral nerve B. A. Dissection of a male showing the general structure ; Fic. 33.—The Cape Crawfish (/asus). B. the nervous system. abdominal artery—vessels which run in close connection with the nerve cord and which supply the limbs and other organs of the body. Examination of a Larval Form (Phyllosoma). Examine under the microscope, or with a lens, a larval form (Phyllosoma) of the Crawfish. Note and draw :—- (a) The large head region, distinct from the thoracic region, and the very small abdominal region. 112 THE FRESH-WATER CRAYFISH—THE CAPE CRAWFISH (b) The two well-developed eyes, and a median eye spot. (c) The antennules. (d) The antenne, with an exopodite and an endopodite branch. (e) The third maxilliped. (f) The first and second walking legs, with well-developed feather-like exopodites. (g) The long third pair of walking legs, with the rudiment of the exopodite on the first segment of the limb. The fourth and fifth walking legs and the appendages of the abdomen have not yet appeared. -- Endopodite {Noa A OY ea Antenna ’ . ¢ / .Exopodite Eye... Exopodite Fic. 34.—Phyllosoma larva of the Crawfish. Enlarged. THE SNAIL (Helix aspersa) External Features. 1. Make a drawing of the Snail, viewed from the right side, to show : (a) The univalve spirally coiled shell (a right-handed conical spiral) within which is the twisted visceral hump containing the chief internal organs. Round the mouth of the shell is the collar, the thickened edge of the mantle. - (6) The head, with two pairs of tentacles and the mouth. The mouth is situated ventrally at the anterior end of the head. The tentacles are retractile ; the upper and larger pair have eyes at their tips, the lower and smaller pair arise in front of the larger ones. (c) The large muscular foot, constituting the organ of locomotion, on which the animal glides. It is the flattened ventral part of the body-wall. ze ren eS UR SRE ree a i yt A ea TI SR iE Poy REDS aio Oa 3 A Fic. 35.—The Snail (Helix aspersa). x 1h. _ (d) The opening of the slime or pedal gland, below the mouth. (e) The genital aperture, situated at the end of a groove along the right side, just below and behind the right large tentacle. (f) The pulmonary or respiratory aperture, situated on the right side in the deep notch of the collar. The anus opens beside the pulmonary aperture. 2. Carefully break and detach the shell. Insert a seeker through the pul- monary aperture and determine the extent of the pulmonary chamber. Fix the Snail down in water by pinning it through the edge of the foot. Make a dorsal-view sketch showing : (a) The mantle, which forms the roof of the pulmonary. chamber and on the underside of which the pulmonary veins are spread out. The mantle secretes the shell. (b) The collar, which is formed by the thickening of the edge of the mantle. 114 116 THE SNAIL (c) The heart, which may be seen from the outside through the mantle. It is situated in the pericardium at the back of the mantle, on the left side; and it has two chambers, an auricle and a ventricle. The main pulmonary vein leads into the auricle of the heart. (ad) The triangular-shaped kidney lying beside the heart. (e) The spirally-coiled visceral region, mainly composed of the brown liver or bilobed digestive gland. (f) The albumen gland, embedded in the liver on the right side. Pulmonary veins 1 Mantle ys" 3 : Cos B ' ' Liver Albumen gland Fic, 36.—The Snail (He/ix). Dorsal view after removal of the shell. (g) The columellar muscle, along the inner side of the spiral. It is attached to the columella of the shell, and it enables the snail to withdraw inside the shell. Internal Structure. 1. Insert the point of your scissors into the pulmonary aperture, and open the pulmonary cavity by cutting round under the base of the collar towards the left-hand side backwards as far as the heart, taking care not to cut through the floor of the mantle-cavity. Pin the mantle over towards the right-hand side. Examine the mantle and note: (a) The heart, consisting of a thin-walled auricle and a muscular pear- shaped ventricle, enclosed in the pericardium. (b) The pulmonary vein, branching over the mantle and leading into the auricle. (c) The triangular-shaped kidney lying next to the heart. (d) The ureter, passing from the kidney and extending along and above the rectum, which opens at the anus situated in the pulmonary aperture. The opening of the ureter is above the anus. (e) The reno-pericardial canal or nephrostome, a narrow ciliated passage between the kidney and the pericardium. Its pericardial opening is opposite the ventricle. 2. Cut through the collar in the middle line and continue the incision back- wards up the spiral and forwards to the region between the large tentacles, 118 THE SNAIL Pin out the collar on each side so as to expose the following internal organs :— A. The Alimentary System. The mouth leads into a swollen pharynx or buccal mass, the ventral floor of which bears the rasping organ or odontophore. (See page 124, Section D.) The pharynx is succeeded by a short gullet or cesophagus, which passes into a large thin-walled crop. On each side of the crop lies a large salivary gland Genital Aperture Dart sac pe Pharynx ---- \ Gisophagus --~ ae Peni: , Mucous glands ae Diverticulum - Oviduct Ve - __- Vas deferens _, Spermathecal Ovotestis i. Liver i cA Hermaphrodite yy x Stomach Rectum -~ i Albu men gland me : 5 \ | Kidney 2 Spermathecal sac AG Pericardium “A... Intestine 1 3 CH \" Ureter f Wise Mi ere, PE? Int. Fic. 37.—Dissection of the Snail (Helix), showing the alimentary and reproductive systems. For Stomach” read “Crop,” and for ‘‘ Intestine” read ‘‘Stomach.” Int. indicates the Intestine. which sends a duct to open into the pharynx. The salivary glands are joined together at their middle by means of a bridge of tissue. Following the crop is the stomach, a somewhat dilated loop into which the ducts from the liver or digestive gland open. Continuing from the stomach is the long intestine, which coils throughout the substance of the liver and passes forward as: the rectum, opening to the outside at the anus, as already noted. B. The Reproductive System. Insert a pin into the large muscular dart sac, and pin it out on the right side of the animal. Put a pin through the loop of the vas deferens, and pin it out on the left side. Note the common duct, a much convoluted tube composed of a 120 THE SNAIL sacculated female or oviducal and a much narrower male or spermaducal channel. Passing elong the top of the common duct is the finer spermathecal duct, which gives off a long coiled diverticulum and is continued on to the base of the albumen gland, where it ends in a swollen sac, the spermatheca or receptaculum seminis. Note the sinuous hermaphrodite duct from the herma- phrodite gland or ovotestis, a yellowish body which lies embedded in the second coil of the liver. The hermaphrodite duct leads into the base of the tongue- shaped albumen gland, where the common duct arises. Trace the common duct forward and note that its male and female portions separate off as a vas deferens and an oviduct. The oviduct is short and thick; it leads into the muscular vagina, into which the spermathecal duct, the dart sac, and a pair of tufted mucous glands open. The vagina opens to the exterior, along with the penis, by the common genital aperture. Trace the vas deferens forward from its point of origin and note that it passes into a muscular penis provided with a long flagellum and a retractor muscle. The penis is protrusible and opens at the common genital aperture. Make a drawing showing the alimentary and reproductive systems. C. The Nervous System. Cut through the cesophagus, just behind the buccal mass, and remove the alimentary tract. Pull the buccal mass forward and pin it down. The supra-cesophageal or cerebral ganglia are incompletely fused and lie over the cesophagus. From each ganglion the following nerves pass off :— (a) The buccal nerve, which enlarges to form a buccal ganglion situated on the posterior surface of the pharynx on each side of the cesophagus. The buccal ganglia are connected by a transverse commissure passing under the cesophagus. (b) The internal labial nerve. (c) The external labial nerve. (d) The facial nerve. (e) A nerve running next to the facial and supplying the anterior body-wall. (f) The optic nerve to the eye tentacle. (g) A nerve passing to the otocyst which lies embedded in the pedal ganglion, The right cerebral ganglion also gives off a nerve, the penial, supplying the penis. Passing round the cesophagus and connecting the cerebral ganglia to the sub- cesophageal mass is a pair of commissures. The sub-cesophageal mass consists of the fused pleural, pedal, and visceral ganglia. The cerebro-pleural commis- sure connects the cerebral to the pleural ganglia, and the cerebro-pedal commis- sure connects the cerebral and pedal ganglia. The pedal ganglia give rise to pedal nerves supplying the foot. The visceral ganglia give rise to a left pallial nerve, a median pallial nerve, and a right pallial nerve (passing over the common duct) to supply the mantle, and a genital nerve supplying the common duct. Make a drawing of the nervous system. 122 THE SNAIL Csophagus a - Salivary duct Pharynx Buccal Ganglion \ External labial ““. » Internal labial ” of Eye >~%- Penis _, Dart sac - Spermathecal duct - Genital Left pallial aa { Fia. 38.—The Nervous System of the Snail (Helix aspersa). C.G. Cerebral ganglia; C.p.c. Cerebro-pedal commissure ; C.pl.com. Cerebro-pleural commissure ; Ot.N. Optic nerve; P.G. Pedal ganglia; Visc. Gang. Visceral ganglia. ---- Median pallial 124 THE SNAIL D. The Odontophore. Make a median longitudinal section through the buccal mass so as to expose the odontophore. The posterior part of the floor of the pharynx is produced backwards into a hollow diverticulum, the radula sac. A chitinous band, the radula cr rasping ribbon, armed on its upper surface with a number of minute rasp-like teeth arranged in transverse rows, is secreted by the epithelial cells lining the ventral wall of the diverticulum. In front of.the radula sac lies a cushion projecting into the cavity of the buccal mass or pharynx. The radula passes over this cushion. The odontophoral cartilage,.which can be moved by the intrinsic muscles, is firmly attached to the cushion. The radula works against the horny jaw situated in the mouth. The radula, the cushion and the muscles together constitute the odontophore. Make a drawing showing the above parts. Odontophoral cartilage t _ Radula Nee Horny jaw et -- Mouth i Opening of 7 i ’ Pedal gland Radula sac Intrinsic muscles Fic, 39.—Inner view of the left half of the head region of the Snail ( Helix), showing the odontophore and associated parts. x 2. THE FRESH-WATER MUSSEL (Anodonta cygnea) THE COMMON MARINE MUSSEL (Mytilus edulis) External Features. Make a drawing of the Mussel, viewed from the left side, to show the following parts :— (a) The umbo, representing the oldest part of the shell, close to the hinge- line, and about a quarter of the length of the shell from the anterior end. The anterior end is more rounded than the posterior end. [In Mytilus the umbo is situated at the anterior end, the pointed end, of the shell. ] (b) The lines of growth, a number of concentric lines parallel to the free margin of the shell and having a common centre at the umbo. (c) The hinge-ligament, occupying the greater part of the straight dorsal surface of the shell, and connecting the two valves of the shell together. (d) The brownish-green periostracum, the thin outer horny layer of the shell. Fic. 40.—The Fresh-water Mussel (Anodonta cygnea). x 1}. (e) The “foot ” (if protruded), semi-transparent, tongue-like, and project- ing between the shells, near the antero-ventral end. [In Mytilus the foot is black and has a byssus attached to its posterior surface. The byssus is a long growth of hairs, each tipped with a small flat disc, by which the animal attaches itself. | (f) The ventral inhalent siphon (if protruded), formed by the projection of the mantle between the shells at the posterior end. The lips bear a fringe of small tentacles. 126 128 FRESH-WATER MUSSEL—COMMON MARINE MUSSEL (g) The dorsal exhalent siphon (if protruded), lying just above the inhalent: siphon. The lips are smooth. [In Mytilus the inhalent and exhalent siphons do not protrude beyond the margin of the shell. | Fie. 41.—The Common Marine Mussel (Mytilus edulis). x Ih. Internal Structure. 1. Place the handle of a scalpel between the ventral edges of the valves of the shell and separate them. The muscles connecting the valves may then be seen. Cut through these as close as possible to their points of attachment to Hinge Anterior retractor Posterior retractor Posterior adductor: Anterior adductor Protracto: Fic, 42.—Inner side of the shell (right valve) of the Fresh-water Mussel (Anodonta), showing the marks of the muscle insertions and the pallial line. the left valve of the shell. Cut through the ligament along the hinge-line, and remove the left shell. Make a sketch of the inside of this shell showing :— (a) The marks of attachment of the following muscles :-— (§, The anterior adductor muscle, a large oval area, close to the 130 FRESH-WATER MUSSEL—COMMON MARINE MUSSEL anterior end of the shell. [In Mytilus there is no anterior - adductor muscle. | (ii) The anterior retractor muscle, a small rounded area, contiguous with the posterior dorsal edge of the anterior adductor. (iii) The protractor muscle, a rounded area behind the lower part of the anterior adductor muscle but quite separate from it. [In Mytilus there is no protractor muscle. | (iv) The posterior adductor muscle, a large oval area, larger than the anterior adductor, near the posterior dorsal end of the shell. (v) The posterior retractor muscle, a small rounded area, continuous with the antero-dorsal edge of the posterior adductor. Anterior, retractor Dorsal, retractors ! ; Posterior wy” retractor 3, ---Posterior ‘ adductor Pallial line Fic. 43.—Inner side of the Shell (right valve) of the Marine Mussel (Mytilus), showing the marks of the muscle insertions and the pallial line. [(vi) In Mytilus there are three dorsal retractor muscles, the impres- sions of which lie along the mid-dorsal part of the shell. | Note that the adductor muscles close the shell, and the other muscles work the ‘‘ foot.” (b) The pallial line, a curved line marking the attachment of the mantle to the shell, and running parallel to the ventral border of the shell. It connects the posterior border of the posterior adductor area with the ventral border of the anterior adductor. (c) The hinge, a smooth longitudinal ridge extending backwards from the umbo along the dorsal edge of the shell. Notice the inner pearly or nacreous layer of the shell. This layer is made by the surface of the mantle which lines the shell. The median prismatic limy layer and the outer horny periostracum are formed by the thickened edges of the mantle. 2. Note the mantle closely lining the inside of the shell and covering the sides of the body. It is attached to the shell along the pallial line. Just behind the posterior adductor muscle the two lobes or flaps of the mantle fuse together, and this fused portion extends forward along the dorsal surface of the posterior 1382 FRESH-WATER MUSSEL—COMMON MARINE MUSSEL adductor muscle a short distance. At the posterior end of the mussel the lobes of the mantle form the exhalent and inhalent siphons above described; and these are the openings of the two chambers into which- the mantle-cavity is divided by a partition at the bases of the gills. 3. Raise the mantle of the left side so as to expose the gills. Note that the gills are long and plate-like (Lameéllibranchiata), and that there is a pair (an outer and an inner gill) on each side between the median “foot” and the mantle. A Branchial filaments Blood vessel Internal ostium External ostium Blood vessel * Fic. 44.—The Fresh-water Mussel (Anodonta). After Parker and Haswell. A. Transverse Section of an outer gill; B. Transverse Section of an inner gill. Each gill consists of two lamelle, continuous along their anterior, ventral and posterior borders. The gill has thus the form of a long and extremely narrow bag open above. The cavity of the gill is subdivided by vertical strands of tissue, the interlamellar junctions, extending between the lamelle and dividing the cavity into a series of water-tubes, which are closed ventrally but open along the dorsal edge of the gill. Each gill has a delicate striation, both horizontally and vertically.. The vertical striation is due to the lamella being composed of a number of fine V-shaped gill-filaments, while the horizontal striation is due to the interfilamentar junctions, horizontal strands of tissue connecting the fila- ments. Between the filaments are minute apertures, the ostia, leading from the mantle-cavity into the water-tubes. The gill-filaments are richly ciliated, and the whole lamella is traversed by blood-vessels. [In Mytilus the gill- filaments are loosely connected by interlocking groups of cilia, the ciliary brushes. Therefore the junctions are ciliary junctions, not solid interfilamentar junctions. | 134 FRESH-WATER MUSSEL—COMMON MARINE MUSSEL 4. Remove the mantle and gills from the left side. Note and draw the following parts :— (a) The foot, a large muscular organ situated at the anterior end of the animal. The foot is axe-shaped (Pelecypoda). [In Mytilus there is a byssus inserted on the posterior surface of the base of the foot. | (b) The pair of labial palps on each side of the mouth. (c) The anterior adductor, anterior retractor, protractor. posterior re- tractor, and posterior adductor muscles. [In Mytilus the anterior adductor and protractor muscles are absent. | (d) The gills of the right side. (e) The mantle lobe of the right side, lining the shell. Keber's organ Pericardium Digestive gland _ Anterior retractor Kidney Posterior retractor Posterior - adduetor Anterior %, adductor Exhalent siphon Inhalent siphon Protractor Mouth Mantle of right side Labial palps Left outer gill Foot Left inner gill Fig. 45.—The Fresh-water Mussel (Anodonta). Shell removed. Part of the mantle of the left side has been taken away so as to expose the gills, foot, etc. (f) The visceral mass forming the upper two-thirds of the large foot, a laterally compressed, oblong mass. The lower third is the muscular portion of the foot, or foot proper. (g) The pericardium, lying along the dorsal surface, beneath the hinge- ligament. Within it is the heart. which consists of two auricles and a ventricle. The ventricle surrounds the rectum, which passes through the pericardium. (h) The paired kidney or “organ of Bojanus,”’ lying just beneath the peri- cardium, with which it communicates through two crescentic reno- pericardial openings (nephrostomes) at the anterior end. [In Mytilus the kidneys lie on the floor of the pericardium on etther side of the heart. | (t) Keber’s organ or the pericardial gland, a glandular. reddish-brown mass, lying in the anterior region of the body just in front of the pericardium. [In Mytilus this gland does not occur. | 136 FRESH-WATER MUSSEL—COMMON MARINE MUSSEL (j) The digestive gland or liver, a large organ surrounding the stomach and the anterior end of the intestine. 5. Expose the heart by opening the pericardium. Note the heart, consist- ing of a single ventricle and a right and a left auricle. The ventricle is a thick- | walled muscular organ surrounding the rectum. Each auricle is a thin-walled triangular sac, the base extending along the dorsal border of the gills, the apex opening into the ventricle. From the anterior end of the ventricle the anterior aorta arises, and runs forwards along the dorsal surface of the rectum to supply the visceral mass. From the posterior end of the ventricle the posterior aorta Reno-pericardial aperture Anterior aorta Left auricle Ventricle Genital aperture \ Pericardium Rectum Renal aperture Digestive gland Stomach Posterior aorta Cerebral ganglion Ureter Kidney proper ms Anus [i k Mouth i Pedal ganglion Water-tubes Visceral ganglion Intestine Cerebro-visceral connective Gonad Fic. 46.—The Fresh-water Mussel (Anodonta) dissected from the left side to show the general structure. After Parker and Haswell. arises, and passes backwards along the ventral surface of the rectum to supply the hinder part of the body. [In Mytilus the auricles are not so apparent, and the aorte are inconspicuous. | 6. Examine the kidney of the left side. It is a wide, thin-walled tube con- sisting of two parts, the one part doubled over on to the other so as to lie dorsally to it. The ventral part forms the kidney proper, while the dorsal forms the ureter or urinary bladder. The ureter opens to the exterior by a small aperture situated between the inner gill and the visceral mass. Just below this aperture may be seen the much smaller genital aperture. The kidney proper opens anteriorly into the pericardium by the crescentic reno-pericardial aperture or nephrostome. [In Mytilus the kidney has a simple structure, and from its posterior end the ureter passes backwards to unite with its fellow from the other kidney, the single duct thus formed opening on the dorsal surface of the posterior adductor muscle. | 188 FRESH-WATER MUSSEL—COMMON MARINE MUSSEL Open the ureter and the kidney proper, and note that they are in com- munication with each other at the posterior end. Note that the vena cava, which carries impure blood to the gills, passes between the kidneys and through their walls. The gonads (ovaries or testes), when ripe, form the greater part of the visceral mass. A. The Alimentary System. Carefully remove the digestive gland so as to expose the stomach. Expose the intestine by carefully cutting away as much of the visceral mass as is necessary. The mouth lies behind the anterior adductor muscle and between the labial palps. It leads into a short and straight cesophagus which passes almost Pericardium Dorsal retractors i H Intestine Cerebro-pedal ee 3H connective Pedal ganglion | . Ureter _Posterior retractor CEsophagus *, Stomach; Anterior *, retractor *, Cerebral ganglion. _. Mouth-.- \ f=\- Posterior -Abdominal pore Fic. 54.—The Dogfish (Acanthias, syn. Squalus). A. Urino-genital system of the female ; B. the male. C. The Skeletal System (part). Remove the skin and muscles from the region between the pectoral fins, and clean the base of a pectoral fin and the pectoral girdle to show the skeleton. Make a drawing to show the following parts :— 1. The Pectoral Girdle. This consists of a hoop of cartilage incomplete dorsally. Its thick ventral portion represents the coracoid, each side of which bears three articular (glenoid) facets for the three basal pieces of the pectoral fin. The incomplete dorsal portions of the girdle represent the scapula. 2. The Pectoral Fins. Each fin articulates with the pectoral girdle by three basal pieces of cartilage—the very small propterygium, the mesopterygium, and the large metapterygium. The propterygium and the mesopterygium each bears a 166 THE SPINY DOGFISH—THE SKATE thick radial; the metapterygium bears several slender radials. These radials bear the horny fin-rays. [In the Skate (Raia) the pectoral girdle is attached to the anterior vertebral plate, and there are three articular facets for the basal pieces of the fin, namely, a large propterygium, a small mesopterygium, and a large metapterygium. | Radials Propterygium Coracoid - fontanelle Mesopterygium Anterior facet Coracoid, Middle facet —_ ¢ Posterior facet Scapula Scapular fontanelle Metapterygium — tS Fic. 55.— Dorsal View of the Pectoral Girdle and Fin Skeleton of the Skate (Raia). From Masterman’s Text-book of Zoology. D. The Vascular System. 1. The Heart and the Afferent Branchial Vessels. Carefully remove the middle portion of the pectoral girdle so as to expose the heart. Extend the opening by removing (in thin slices) the ventral wall of the pericardial cavity. Note that the heart, situated in the pericardial cavity, is composed of four parts. Posteriorly and dorsally is the small thin-walled sinus venosus, opening in front into a single large and thin-walled atrium or auricle. The auricle communicates with a thick-walled ventricle, from which is given off in front a tubular chamber with thick muscular walls, the conus arteriosus. To see the sinus venosus properly, press the ventricle forwards. | Cut away or tear apart the covering muscles in front of the conus so as to expose the ventral aorta. This vessel is a continuation of the conus arteriosus, and passes forward between the gills. Trace the ventral aorta forward to near the middle of the lower jaw, and by carefully clearing away the tissue and muscles from its vicinity, expose the five afferent branchial vessels (on each side) from the aorta to the gills. Trace out these arteries, noting that the first or anterior branchial artery goes to the half-gill of the hyoid arch, and the other 168 THE SPINY DOGFISH—THE SKATE four branchial arteries go to the gills of the first four branchial arches. The fifth branchial arch is without a gill. Notice the thyroid gland lying at the anterior end of the ventral aorta. Note that each end of the sinus venosus passes into a short duct of Cuvier. The large posterior cardinal sinus, which extends forward dorsally from Conus J arteriosus-{7 Pericardial e : , yo Pectoral girdle cavity = “| cut through | Sinus venosus \ Fic. 56.—The Dogfish (Acanthias, syn. Squalus). Afferent Branchial or Ventral Arterial System. between the kidneys, opens into the duct of Cuvier at each side. The anterior cardinal sinuses, which extend from around each eye and above the gill-arches, also open into the duct of Cuvier opposite the posterior cardinal sinus openings. The hepatic sinus of the liver opens (two openings) into the posterior wall of the sinus venosus. Slit open the sinus venosus, and pass a seeker into these sinus openings. Note that the pericardium is a portion of the ccelome or body-cavity which has been separated off. It is, however, in communication with the main cavity 170 THE SPINY DOGFISH —THE SKATE (peritoneal or abdominal cavity) by the pericardio-peritoneal canal, which opens in front, in the middle line, above the sinus venosus. Find this opening, and pass a seeker along the canal (on the ventral surface of the cesophagus). Make a complete sketch showing the heart, ventral aorta, anid afferent branchial vessels. ‘ [In the Skate the heart also consists of four parls—viz. the sinus venosus, auricle, ventricle, and conus arteriosus or pylangium. Connected with the anterior end of the pylangium is the synangium or bulbus arteriosus, which gives off the median ventral aorta. The ventral aorta passes forwards in the middle line and gives off the anterior and posterior innominate arteries. Each anterior innominate artery divides into two afferent branchial vessels which convey blood s . . ; “Synangium yi--Ventricle & 4--Pericardial 5 cavity Fic. 57.—The Afferent Branchial or Ventral Arterial System of the Skate (Raia). I, Anterior Innominate Artery; II. Posterior Innominate Artery. to the half-gill of the hyoid arch and the gill of the first branchial arch. The posterior innominale arlery divides into three branches conveying blood to the gills of the second, third and fourth branchial arches. | 2. The Efferent Branchial Vessels and Dorsal Aorta. Cut through the angle of the mouth on the right side and carry the incision backwards through the middle of the gill-clefts of that side. Turn the whole of the lower jaw over to the left side, and wash out the mouth. Carefully remove the mucous membrane from the roof of the mouth, working from the cesophagus forwards. The efferent branchial vessels will then be seen. There are four pairs, and these all join to form the median dorsal aorta, which passes backwards along the mid-dorsal line of the body. Trace each efferent vessel from the aorta to the gill. In Acanthias the first pair of efferents unite just between the fourth gill-clefts. From each a small artery is given off which soon disappears into the cartilage. This vessel probably corresponds to the vertebral artery of the Skate. Where the first efferent vessel forms a loop around the first branchial cleft, it gives off an artery corresponding to the common carotid of Raia and Scyllium. This common carotid runs along 172 THE SPINY DOGFISH—THE SKATE the inner side of the spiracle and upper jaw, joins its fellow of the other side in the middle line, then disappears in the cartilage of the skull. The second, third and fourth efferent branchial vessels from the gills all converge to join the dorsal aorta, Between the origin of the third and fourth pair of efferent vessels a Common carotid Spiracle peas, IQA ON Gills cut AX" through Gey % NS h?=-Subclavian j Pectoral girdle cut through --Dorsal aorta Fic. 58.—The Dogfish (Acanthias, syn. Squalus), Efferent Branchial or Dorsal Arterial System. subclavian artery is given off on each side, passing backwards to the pectoral fin. Posterior to this the .aorta gives off the cceliac artery already referred to. Make a complete drawing of the efferent branchial vessels and the dorsal aorta. [In Scyllium the first pair of efferent vessels unite to form the aorta between the Jirst gill-clefis. At first each vessel forms a loop round the first gill-cleft. The 174 THE SPINY DOGFISH--THE SKATE remaining three pairs of efferent vessels are similar and form loops round the second, third and fourth gill-clefts. There is a half-loop or single vessel on the anterior side only of the fifth gill-cleft, as this cleft has no gill on its postertor side. This vessel is joined at its middle to the loop round the fourth gill-cleft. The loops are all connected with each other at about the middle of their lengths by short hori- zontal vessels passing across the gill-arches. From the inner anterior end of the first loop of each side a common carotid artery arises. These carotids curve for- wards and inwards along the inner surface of the floor of the skull, each dividing into an external and an internal carotid artery. The former runs forwards to supply the upper jaw and snout. The latter passes inwards to the mid-ventral line, where the two internal carotids cross each other, unite with the hyotdean artery, and supply the brain. The dorsal aorta is prolonged anteriorly in the middle line ; and it bifurcates to form the pair of posterior carotid arteries, each of which joins a common carotid artery just where that vessel divides into external and internal carotids. From the middle of the anterior half of the first loop, and in line with the short horizontal vessels, the hyoidean artery arises; it runs forwards dorsal to the hyomandibular cartilage, passes to the spiracle to supply the pseudobranch, and enters the cranium by a small foramen in the inner wall of the orbit, and jotns the internal carotid. | [In the Skate (Raia) the efferent vessels form loops round the first four gill-clefts, Just as in Scyllium. After leaving the clefts, the first and second efferent branchial vessels unite into one, and thus only three pairs of main efferent vessels join to form the dorsal aorta. The fifth gill-cleft has a small vessel on its anterior side, this vessel being connected by a short horizontal vessel with the loop round the fourth gill-cleft. The first efferent vessel gives off a vertebral artery, similar to that in Acanthias, passing to the brain and spinal cord. There is only a small hyoidean artery, which passes to the side of the hyomandibular cartilage and does not take a course as in Scyllium. The dorsal aorta is not produced anteriorly as in Scyllium, but resembles that of Acanthias. The common carotid artery resembles that of Acanthias and Scyllium. The dorsal aorta gives rise to a pair of subclavian arteries to the pectoral fins. | -~External carotid Internal carotid Internal carotid , External carotid Hyoidean -Spiracle Raster - ----4,-Common carotid - -Common carotid--- Subclavian -Dorsal aorta Doreal aorta Fic, 59.—The Efferent Branchial or Dorsal Arterial System (A.) of the Skate (Raia) ; and (B.) of the Dogfish (Scyllium). 176 THE SPINY DOGFISH —THE SKATE Third Day E. The Skeletal System (continued). . Remove the integument from the head and branchial region so as to expose the skull and the visceral arches. There are seven visceral arches, forming the supporting framework of the branchial region (pharynx). The first is the mandibular, represented by the upper and lower jaws, and the second is the hyoid, which is divided into an upper or hyomandibular portion, attached to the skull and serving (as the suspensorium) to connect the jaws with the cranium, and a lower portion, the hyoid proper or cerato-hyal. The other five are the branchial arches, and each is divided into four segments. C: hy. “ Be w lL Fi. 60.—Skull and Visceral Arches of the Dogfish (Scylliwm) as seen from the left side. After W. K. Parker. Cr., Cranium ; Olf. ep., Olfactory capsule; Aud. cp., Auditory capsule; Up. j., Upper jaw or palato-pterygoid cartilage; L.j., Lower jaw (Meckel’s cartilage); Lg., Ligament; Hym., Hyomandibular; C, hy., Cerato- hyal or hyoid proper; Br. a. 1 to Br. a. 5, Branchial arches, F. The Nervous System. Slice away the cartilaginous cranium so as to expose the brain, taking care to leave the eye and the auditory organ (otocyst) of the left side uninjured. Note the olfactory capsules lying over each nostril. 1. The Brain. (a) The olfactory lobes lie close to the olfactory capsules, and are connected to the cerebral hemispheres, each one by a long stalk. (b) The cerebral hemispheres (prosencephalon) are fused together to form the anterior part of the brain. (c) The thalamencephalon is the insunk part behind the cerebral hemi- spheres. It has a thin roof with a choroid plexus of blood-vessels. Its narrow cavity is the third ventricle, and its thick side-walls are the optic thalami. From the posterior part of its roof a slender stalk-like outgrowth, the pineal organ or epiphysis, projects forward. An outgrowth from its floor is the infundibulum 178 THE SPINY DOGFISH—THE SKATE (with the inferior lobes and the saccus vasculosus). The pituitary body (hypophysis) is attached to the under-surface of the infundibulum. (d) The optic lobes overlie the posterior part of the thalamencephalon, and represent the thick bulged-out roof of the mid-brain, the side-walls of which are the crura cerebri and its cavity is the iter. (e) The large ovoid cerebellum partly covers the optic lobes in front and the medulla behind. It represents the thickened front part of the roof of the hind-brain. (f) The medulla oblongata, partly covered by the cerebellum, forms the posterior part of the brain. It is produced forwards along each side (restiform bodies), and is continuous behind with the spinal cord. Its cavity is the fourth ventricle. Note that (a), (b) and (c) represent the cerebrum or fore-brain, (d) represents the mesencephalon or mid-brain, and (e) and (f) represent the rhombencephalon or metencephalon or hind-brain. ~- Olfactory capsule j \_--Olfa lob Superior ophthalmic / EE ene ¥ & Vil psesers: “Cerebral lobe / i _- Buceal VII Inferior ophthalmic V/-; * \.. Thalamencephalon Inferior oblique--- Superior oblique--//, Anterior rectus-7- Pathetic IV--f- Superior rectus~ f -- ‘-4-- Optic IT -- a \---Optic lobe .--Maxillary V =+* Cerebellum aah Superior Oe . V & VII --Mandibular V \ “Palatine Vil --Spiracle --Mandibular VII Hivomandibulse VII oo VII lossopharyngeal Ix Inferior rectus--(-\ - Corpora restiformia, Posterior rectus-] Spiracle--t: Semi-circular canal of Ear- {7 " Visceral X Fic. 61.—The Dogfish (Acanthias, syn. Squalus). Brain (dorsal view), Cranial Nerves, and Eye Muscles. 180 THE SPINY DOGFISH—THE SKATE Fic. 62.—Ventral View of the Brain of the Dogfish (Acanthias). After Purser. With permission from J. Graham Kerr’s Zoology Jor Medical Students. 01,, olfactory bulb; 7.1., inferior lobe; it., pituitary body ; II-X, Roots of Cranial Nerves. 2. The Cranial Nerves. The following is a list of the cranial nerves and their chief branches :— I. Olfactory. II. Optic. III. Oculomotor. IV. Pathetic. “Wwadsruy ~2 (a) Superior ophthalmic. (b) Inferior ophthalmic. (c) Maxillary. (d) Mandibular. V. Trigeminal VI. Abducent. (a) Superior ophthalmic. (b) Buccal. (c) Palatine. (d) Hyomandibular. VIII. Auditory. IX. Glosso-pharyngeal. VIL. Facial (a) Branchial. _ X. Vagus (° Visceral. Reagan (c) Lateral. : In dissecting out the cranial nerves and the eye muscles it is best to do so in the following order :—- (i) The olfactory nerve (I), represented by a number of fine branches arising from the anterior end of each olfactory lobe and passing at once into the olfactory capsule, where they become distributed to the epithelium of the olfactory organ. (ii) The pathetic nerve (IV), arising from the dorsal surface of the brain, be- tween the anterior part of the cerebellum and optic lobes, and passing 182 THE SPINY DOGFISH—THE SKATE into the cartilage of the skull. Cut away the cartilage above the eye until the superior ophthalmic branch of the trigeminal nerve (V) is exposed. This ophthalmic nerve represents the fused ophthalmic branches of the trigeminal nerve (V) and the facial nerve (VII). Trace this branch from its origin over the eye muscles to the snout. Follow the pathetic, which passes under the ophthalmic, to the aver oblique eye muscle. (iti) Cut away the cartilage further down between the eye and iis brain, and note the optic nerve (II) passing straight from the brain to the eye. (iv) Note the upward cartilaginous projections of the upper jaw between the superior ophthalmic branch and the sides of the skull. (v) Make out the following eye muscles :--- (a) The two oblique muscles, arising close together at the anterior part of the orbit and inserted widely apart on the anterior half of the eye, the superior oblique on the dorsal surface and the inferior oblique on the ventral surface. (b) The four recti muscles, arising close together at the posterior part of the orbit and inserted mostly on the posterior half of the eye, the superior rectus on the dorsal surface, the inferior rectus on the ventral surface, the posterior rectus or rectus externus on the posterior surface, and the anterior rectus or rectus internus, which passes behind the eye and between the two oblique muscles, and which is inserted on the anterior surface of the eye. (vi) The oculomotor nerve (III), arising from the under-surface of the mid- brain, passing through the wall of the skull, and supplying the follow- ing eye muscles: the inferior oblique, the superior and the inferior and the anterior rectus. (vii) The inferior ophthalmic or ophthalmicus profundus branch of the trigeminal nerve (V), passing over the eye under the superior rectus and the superior oblique muscles, and going forwards to the snout. [This branch is absent in Scyllium.] ‘Trace both the ophthalmic branches back to their origin. Raise the eye and note, passing along the floor of the orbit, the maxillary branch of the trigeminal nerve (along with the buccal branch of the facial nerve) to the upper jaw. Make out the mandibular branch of the trigeminal nerve, arising behind the maxillary and passing through the cartilage to the lower jaw. (viii) Slice away the cartilage alongside the spiracle so as to expose the semicircular canals of the ear (otocyst), and make out the following nerves arising together with the trigeminal (V) from the side. of the medulla, anteriorly :— (a) The hyomandibular branch of the facial nerve (VII), passing between the spiracle and the hyomandibular cartilage, and dividing into an external mandibular nerve to the lower jaw and a hyoidean nerve to the hyoid arch. 184 THE SPINY DOGFISH—THE SKATE (b) The palatine branch of the facial nerve (VII), passing forwards from the hyomandibular branch in front of the spiracle and going obliquely across the floor of the orbit to supply the roof of the mouth. [In the Skate (Raia) the facial nerve (V11) gives off the following branches :— (a) The superior ophthalmic, which is fused with the superior ophthalmic of the trigeminal and which supplies the snout (sensory ampulle). (b) The inner buccal, which runs under the eye and through the nasal capsule to the inner buccal ampulle. (c) The outer buccal, which runs under the eye, external to the olfactory capsule, and goes to the outer buccal ampulle. (d) The palatine, passing downwards in front of the spiracle, and supplying the roof of the mouth. It gives off a small prespiracular branch to the front of the spiracle. (e) The hyomandibular, passing outwards behind the spiracle and the man- dibular muscle, and giving off the following branches :— (a) The recurrent facial, running external to the auditory capsule. (8) The internal mandibular or “ chorda tympani,” going under the sptracle to the inner side of the jaw. (v) The facial proper, supplying the muscles of the hyoid arch. (6) The hyoidean or postspiracular, passing downwards to the muscles and ampulle of the hyoid arch. (e) The external mandibular (a branch from the hyoidean), passing behind and round the mandibular muscle to the mandibular ampulle. | (c) The auditory nerve (VIII), arising behind the facial nerve from the side of the medulla and passing directly into the auditory capsule, and in its course crossing the- glosso-pharyngeal nerve (IX). (ix) The glosso-pharyngeal nerve (TX), arising from about the middle of the medulla oblongata, and passing back across the floor of the auditory capsule to supply the first gill-cleft. (x) The vagus or pneumogastric nerve (X), arising Just behind the glosso- pharyngeal nerve, by several smaller roots which fuse together to form a conspicuous nerve. The vagus divides into a branchial nerve, which gives off four branches supplying the second to fifth gill- clefts, and a lateral nerve running along the side of the body and supplying the lateral line. After giving off the branchial branches to the gill-clefts, the branchial nerve passes backwards as the visceral nerve to the heart and stomach and other viscera. Slit open the anterior cardinal sinus to show the branchial branches passing along its inner wall and across the floor. (xi) The abducent nerve (V1), a small inconspicuous nerve completely con- cealed by the brain. It can be seen under the posterior rectus muscle, which it supplies ; and it may be traced below the inferior ophthalmic 186 THE SPINY DOGFISH—THE SKATE to the under-surface of the medulla, where it arises between the roots of nerves V and VII and the mid-ventral line. Make a complete drawing of the brain, cranial nerves, and eye muscles. Olfactory capsule Se Anner buccal VII Olfactory lobe---~-- a IV Maxillary V fg” ge oes Superior Tila. Cerebral lobe Vig Anterior rectus: N \ i ig Thatamencephalon Superior rectus” aS , Mandible Inf. ophthalmic V-/--7—— eM muscle Posterior ZectiaVPS 67%, \ Presp.VII Oculomotor IIF > Sk Palatine vit “Reourtent facial ,Hyom, . Vil ~.. WHyoidean VII I _— Facial proper VII Auditory capsule- Optic lobe Cerebellum” .” Corpora restiformia’ Glossopharyngeal IX Medulla oblongata” Hy yA Lateral X---} |? I, Visceral X Hy Fic. 63.—The Brain (dorsal view), Cranial Nerves, and Eye Muscles of the Skate (Raia). II. Optic nerve; IV. Pathetic nerve; VI. Abducent nerve; Ext, mand. VII. External Mandibular branch of Facial nerve; Hyom. VII. Hyomandibular branch of Facial nerve; Int. m. VII. Internal Mandibular branch of Facia) nerve; Presp, VII. Prespiracular branch of Facial nerve; VIII. Auditory nerve; Spir. Spiracle. Examine one of the auditory organs or otocysts. Carefully remove the cartilage of the auditory capsule of the skull until the parts of the otocyst are exposed. It consists of three semicircular canals, an endolymphatic duct, otoliths (limy matter) in the lower part, and endolymph throughout the cavity and within the canals. Between the otocvst wall and the cartilaginous auditory capsule is the perilymph. THE FROG (Rana) THE PLATANA or CLAWED TOAD (Xenopus) First Day External Features. : 1. Make a drawing of the dorsal surface of the Frog (or the Toad), showing : (a) The nostrils or external nares. (6) The eyes, each with two eyelids. The upper eyelid is well developed, pigmented, and almost immovable; the lower one is a mere fold of skin, produced into a thin, transparent and freely movable nictitating membrane. [In the Platana there is also a short tentacle beneath the eye. | (c) The circular tympanic membrane, situated just behind the eye. [This is absent in the Platana. | (d) The opening of the cloaca, on the dorsal surface and between the legs. [In the female Platana there are three conspicuous folds of skin around the cloaca. | (e) The limbs and their divisions. [(f) In the Platana the skin has tube-like lines round the body. These are the openings of the slime glands, with which the skin is richly supplied. | HA f , \ Fic. 64.—A. The Frog (Rana), nat. size; B. The Platana or Clawed Toad (Xenopus), reduced. 2. Make an enlarged drawing, about twice the natural size, showing : (a) The fore-limb, consisting of upper arm, fore-arm, and hand with four complete digits (the first digit, the pollex or thumb, being an incon- spicuous rudiment). 188 190 THE FROG—THE PLATANA (b) The hind-limb, consisting of thigh, shank or leg, and foot with elongated ankle-region and five webbed digits, the shortest one being the hallux or ‘‘ great toe.” [In the Platana the inner three digits have claws. | Name the parts of the limbs, and number the digits from within outwards. Mouth Cavity. Open the buccal or mouth cavity widely, and make a sketch showing : (a) The teeth on the upper jaw. (b) The teeth on the vomers. [There are no vomerine teeth in the Platana.] (c) The internal nares or internal openings of the nostrils. (d) The pair of Eustachian apertures, at the angles of the mouth. [Jn the Platana there ts a single Eustachian aperture. | (e) The tongue. [Absent in the Platana. | (f) The glottis, the slit-like opening of the larynx which leads from the lungs. (g) The gullet. Pass a seeker into the Eustachian aperture, along the Eustachian tube and through the tympanic membrane. [In the Platana, owing to the complemity of the Eustachian tubes and the bony form of the ear, cavity, it is not possible to do this. ] ~Gullet Gullet ~Glottis “ Glottis’~ Sy Fic. 65.—A. Buccal or Mouth Cavity of Rana; and B. of Xenopus. Muscular System and Vascular System (part). 1. Lay the Frog on its back under water in the dissecting-dish, and fix it firmly by pins through the limbs. Using scissors, cut through the skin along the middle line, the whole length of the body. Reflect the skin on each side and pin it down, noticing its loose attachment and the subcutaneous lymph spaces. Make a drawing showing: . (a) The muscles. (i) Two pectoralis muscles, each consisting of two portions passing _to the upper arm; one portion arising from the sternum, the other from the outer side of the rectus abdominis muscle. 192 THE FROG—THE PLATANA Cut through the latter portion close to the arm, and fold it backwards to expose the underlying brachial vein. (ii) Two recti abdomini muscles, one along each side of the mid- ventral line of the body, and there separated by the white line (linea alba). Each rectus abdominis muscle is trans- versely divided into bellies. (iii) The deltoid muscle to the arm. (iv) The mylo-hyoid muscle, on the underside of the mouth region. (v) The obliquus-externus muscles (which cover the sides of the body) underlying the recti abdomini and the abdominal portions of the pectoralis muscles. (b) The musculo-cutaneous vein, lying under the pectoralis muscle. It joins with the brachial to form the subclavian vein ; and it is formed by branches from the skin and muscles in the region of the arm. [In the Platana the muscular and cutaneous veins do not join to form one. There is a second cutaneous vein arising from the skin of the abdomen and joining the abdominal vein. Two small cutaneous veins are seen on the skin of the leg, and another on the skin under the lower jaw. | (c) The abdominal vein, visible through the body-wall as a dark longi- tudinal line between the recti abdomini muscles. Before it enters the liver, it receives the hepatic portal vein from the gut and spleen. (d) The brachial vein of the arm. Near it is the white brachial nerve, which may often be seen. Try to trace the point of junction of the brachial and musculo-cutaneous veins, or the brachial, muscular, and cutaneous veins in the Platana, as shown in the figures. Mylo-hyoid muscle e: Mylo-hyoid’ Pectorali Brachial veln} Musculo-cutaneou: ty vein... , Deltoid muscte "AyZ] ~ Rectus-abdominis musc . \ Skin ++ Obliquus-externus muscle Pectoralis muscle cut away from its insertion, and reflected A B Fic. 66.—A. Muscular System and Vascular System (part) of Rana; and B. of Xenopus. 194 THE FROG—THE PLATANA 2. Make an incision in the body-wall, slightly to the right side of the abdominal vein, which may then be seen clearly on the inner side of the body- wall. Carefully detach this vein from the abdominal wall. Remove the skin from the legs. Second Day Skeletal System (part). 1. Remove the upper portions of the pectoralis muscles, covering the part of the body between the arms, to show the bones and cartilages of the central part of the shoulder girdle and sternum, viz. : (a) The thick coracoids. (b) The more slender clavicles anterior to the coracoids ; and both extend- ing, on each side, from the base of the arm towards the centre of the body. (c) The sternum, consisting of a median row of cartilages which are believed to be derived from the shoulder girdle. It does not, therefore, corre- spond to, or is not homologous with, the sternum of the Pigeon or the Rabbit, which is derived from the ribs. The sternum consists of the following parts :— (i) The omosternum, consisting of two parts—viz. an anterior cartilaginous part (sometimes called the episternum) and a posterior bony rod (the omosternum proper). (ii) The two cartilaginous epicoracoids. (iii) The metasternum, consisting of two parts—viz. an anterior bony part (sometimes called the mesosternum or sternum) and a posterior cartilaginous part (sometimes called the xiphisternum). [In the Platana the sternum consists of the following parts :— (i) The two cartilaginous epicoracoids. (ii) The metasternum, which is broad and consists of cartilage only.| Make a sketch of the pectoral girdle. (See Fig. 76, A or B, page 218.) 2. Cut through the coracoids and clavicles on each side, close to the base of the arm, and carefully remove this part of the pectoral girdle and sternum so as to expose the heart lying beneath. Alimentary System. Make a sketch showing the heart, lungs, liver, gall-bladder, bile-duct (common duct of liver and pancreas) going to the duodenum, exposed parts of the stomach, duodenum, small intestine (or ileum), large intestine (or rectum), pancreas, spleen, and urinary or cloacal bladder. THE FROG—THE PLATANA 196 ‘oqo ‘tuaqsg ArejUeMITY ey3 Moys 03 ‘sndoway Jo ‘gq pue ! nUNY Jo UOTJOOSSIC] “W-—"L9 “DIT Vv ~~ TOpprid WIdA LVQuNy-ON] . | -" ulad [eqtod [Rua : - mn4oey ULGA [BULOPAY - - ¢ wnuepoudg _-- WOd{] sealourg --f ----uvaldg qonp-ella 4 --- Koupry ypeuoyg -- + > -18pperq TO Suny --- TOA] - --£-}--==- qaeap -- $-/-----= WIA TBPNOSUT f19q1e : ; > ee) snoauvno-owm[ud — yore o1t94SAg - purls pryoreD ~~~ “eAromt [essos0d A *s ulea rvndvosqng + BAMAU SUS A a\.lew [adUAIeYd-Osso[y Alayle pryoleg — . Aloe [VNU] ~ ULOA IBNSNE [VUIIXG UWIaA IEpUsUl [eUTeZUT _-UI@A [BIOW OT --UI8A O19RI0g snio[ kg } A ePPel 2 -wnyoeay UIdA [VUTWOpPG Vy - WI9A [Vy10d [eUay winuepong - A. wune]] svatourg - --- \ _-use]dg qoup-erte-- _o-\ SOUP youmoys -- Joppriq-TleD UIaA snoeueynd-o[NdsN]L -- WA [BNpoVIg, qvay!>~ Alay Snoatteynd-our [Ud --— yore o1umeysAg -- > ALIL.LV PlJOLVD - > ULAA UBIABPOQNUS * uaa Tepadvosqug “-@aaau [RIOR UIaA IvpUsHl [vUusEyUT aATeU SUBBA Jos UJAA TBTNQIpusyl eAdau [vasusavyd-ossoly PULLS plqoIND AlOPR PVUSULT, pues promy R N . = Urea TeUSUTT UIOA AB[NANl [VUIeNG” SN A 7d ~aarou [vsso[sod.AR 198 THE FROG—-THE PLATANA Third Day Muscular System and Vascular System (continued), and Nervous System (part) A. Muscular System. In order to facilitate the location of the veins and arteries of the hind-limhs, it is necessary to make out the following muscles :— 1. Muscles of the Thigh (ventral surface) : (a) The sartorius, a long flat muscle arising from the lower end of the ilium, and inserted into the inner side of the head of the tibia. (b) The vastus internus, a large muscle arising from the ventral and anterior border of the acetabulum, and lying partly under the sartorius on the outside of the thigh. (c) The rectus internus major, a large muscle arising from the ischium, occupying the inner side of the thigh and inserted into the head of the tibia. It is covered distally by the sartorius. (d) The adductor magnus, a large muscle arising from the pubis and ischium. It lies between the sartorius and the rectus internus major, and is con- cealed by these muscles distally where it becomes inserted into the femur. 2. Muscles of the Shank (ventral surface) : (a) The gastrocnemius, a large spindle-shaped muscle forming the calf of the leg. It arises mainly from the hinder side of the distal end of the femur ; and it ends in the long and slender tendo Achillis, which passes under the ankle joint and into the sole of the foot. Vastus internus , ’ Tibialis, anticus : - Sartorius _eommme, Tibio-fibula A 1 1‘ t ae . ' Pevveneit o ' Rectus internus major ; Tibialis posticus ‘ ' é Adductor magnus Gastrocnemius Sartorius Extensor cruris ‘ : i aga ye aug! Rectus anticus femoris Tibialis angie i 3 ' B ‘ a 1 Adductor magnus | Rectus internus major Fic. 68.—A. Muscles of the Left Hind-limb of Rana; and B. of Xenopus, from the ventral surface. 200 THE FROG—THE PLATANA (b) The tibialis posticus, lying between the gastrocnemius and the tibio- fibula and running along the whole length of the tibio-fibula. (c) The tibialis anticus, on the outer side of the leg. (d) The extensor cruris, lying between the tibialis anticus and the tibio- fibula. 3. Muscles of the Thigh (dorsal surface) : (a) The rectus anticus femoris, occupying the outer dorsal surface of the thigh, arising from the ilium in front of the acetabulum and covering the vastus internus. ; (b) The vastus externus, occupying the median dorsal part of the thigh and arising from the posterior dorsal edge of the ilium. These two muscles (a) and (b), along with the vastus internus of the ventral surface, join together to form the triceps extensor cruris, the great extensor muscle of the thigh, which is inserted into the tibia just below the head of that bone. (c) The semimembranosus, a stout muscle occupying the inner surface of the thigh, and arising from the dorsal part of the ischium. It is inserted into the back of the head of the tibia. (d) The biceps, a long slender muscle almost completely covered by the vastus externus and the semimembranosus. 4. Muscles of the Shank (dorsal surface) : (a) The gastrocnemius. (b) The peroneus, a stout muscle occupying the outside of the leg between the tibialis anticus and the gastrocnemius. [The muscles of the hind-limbs of the Platana are very similar to thos: of the Frog, except that the rectus anticus femoris extends on to the ventro-lateral surface of the thigh so as to cover almost the whole of the vastus internus. In the shank. the tibialis posticus 1s much enlarged and covers the tibio-fibula completely. | Vastus externus Semimembranosus \ Cloaca i Gastrocnemius Z = : Er” A Gluteus ¥ SSS if ) 1 Rectus anticus femoris | Biceps \ Triceps extensor femoris Semimembranosus Vastus externus i Rectus internus minor N Gastrocnemius £ B 2 ’ Ss \ ' iC on ‘ ! Tibialis anticus ' Vastus internus , Perdgneus Rectus anticus femoris Biceps Fic. 69.—A. Muscles of the Left Hind-limb of Rana; and B. of Xenopus, from the dorsal surface, . 202 THE FROG—THE PLATANA B. Venous System and Nervous System (part). 1. Note :— (a) The heart within a thin pericardium, and consisting of the sinus venosus, the two auricles (divisions of the atrium), the single ventricle, and the conus arteriosus which is continued into the ventral aorta (the ““truncus ’’) which divides into two branches. Remove the pericardium from the heart and tilt the apex of the heart forwards, noting the dorsal and roughly triangular sinus venosus into which the right and the left superior vene cave (or precavals) and the single inferior vena cava (or postcaval) open. (b) The veins passing from each side of the sinus venosus. Each superior vena cava is formed by the union of the following branches :— (i) The external jugular vein, formed by the union of the lingual vein from the tongue and the mandibular vein from the margin of the lower jaw. (ii) The innominate vein, formed by the union of the internal jugular vein from the head and the subscapular vein from the back of the arm and shoulder. (iii) The subclavian vein, formed by the union of the brachial vein from the fore-limb and the musculo-cutaneous vein from the muscles of the body and from the skin. [In the Platana the superior vena cava is formed by the following vessels :— (i) The external jugular vein, which passes under the mylo-hyoid muscle, from the region of the tongue and mandible. (ii) The internal jugular vein, which runs on the under side of the Jloor of the mouth, parallel to the external jugular. (ili) The thick subscapular vein from the shoulder. As the internal jugular and the subscapular veins join the precawal vein separ- ately, there is no innominate vein. (iv) The subclavian vein, which is formed by the brachial vein from the arm, a cutaneous vein from the skin, and a muscular vein Jrom the abdominal muscles. The muscular and the cutaneous veins are separate. consequently there is no musculo-cutaneous vein. | (c) The hypoglossal (spinal nerve IT) and the glosso-pharyngeal nerves, both running alongside the lingual vein. [In the Platana the glosso-pharyn- geal nerve runs along the inner side of the lower jaw, while the first spinal nerve (corresponding to the hypoglossal of the Frog) curves inwards to supply the mylo-hyoid muscle. | (d) The vagus nerve, supplying the heart and lungs and stomach. It emerges just posterior to the glosso-pharyngeal, and closely follows the course of the internal jugular vein. [In the Platana it follows the course of the subscapular vein. | Make an enlarged drawing showing the above parts. (See Fig. 67, A or B, page 196.) 204 THE FROG—THE PLATANA 2. Note the inferior vena cava (postcaval vein) receiving the renal veins from the kidneys and the hepatic veins from the liver, and opening into the sinus venosus. Precaval vein ‘ i Veatricle_ gate Sinus vengsus / Pry * § ---Liver ~Hepatic portal--- Abdominal Abdominal NS \\N \\ \ \--Femoral \ Fic. 70.—A. Venous System (posterior part) of Rana; and B. of Xenopus, from the ventral aspect. The ventricle of the heart is tilted forwards to show the sinus venosus. The veins of the legs, being on the dorsal side, are shown in broken lines, 3. In order to make out the femoral and sciatic veins, turn the Frog over so as to have the dorsal surface uppermost. Carefully separate the rectus anticus femoris muscle from the vastus externus muscle so as to expose the femoral vein ; it lies between the vastus internus and the vastus externus, where it may be traced back a short distance, then gradually towards the inside of the thigh, under the vastus externus and biceps muscles. It follows the course of the biceps muscle, passing on to the ventral surface of the leg at the knee, just where the gastrocnemius muscle meets the semimembranosus. Note the ramus communicans iliacus, a small vein on the anterior ae a surface of the thigh just at the origin of the vastus externus muscle. It is a vessel communicating between the femoral and the sciatic veins. Carefully separate the biceps muscle from the semimembranosus so as to expose the sciatic nerve. It divides into two branches at the anterior end of the biceps. The main branch, next the biceps muscle, divides just above the knee into the tibial and peroneal nerves supplying the leg and the foot respec- tively ; the other branch passes under the semimembranosus, and, as it supplies that muscle, tt may be named the semimembranosus nerve. Following the 206 THE FROG—THE PLATANA dorsal surface of the main branch of the sciatic nerve, note the iliac artery, and also the sciatic vein alongside the semimembranosus nerve. Now lay the Frog on its back, and trace the femoral and the sciatic veins forward. Note that these vessels join together a short distance behind the posterior end of the kidney to form the renal portal vein, which extends along the outer side of each kidney. Opposite the kidney the renal portal is joined by the dorso-lumbar vein, which drains the blood from the back and the lumbar region. Just anterior to the point of insertion of the vastus internus muscle the femoral vein gives rise to the pelvic vein, which runs over the anterior end of the sartorius muscle and joins its fellow in the middle line to form the abdominal vein, already noted in the first day’s work. [In the Platana the femoral vein lies on the surface of the leg between the vastus externus and the semimembranosus muscles. Trace the femoral vein back along the leg. Carefully separate the biceps muscle from the semimembranosus, and expose the sciatic nerve. This nerve also branches into two, as inthe Frog. Follow- ing the dorsal surface of the main branch, note the iliac artery ; and, on the ventral surface of this nerve, note the sciatic vein. The smaller branch of the sciatic nerve appears to run under the semimembranosus muscle to supply the rectus internus minor muscle. Just anterior to the origin of that nerve, the sciatic vein joins the femoral vein to form the renal portal vein which passes forwards to the kidney. A short distance anterior to its origin, the renal portal gives rise to a pelvic vein which ~-Abdominal \ ~ “on fs Femoral. - -/- - Sciatic Sciatic nerve-- j f f Abdominal BIoccrst Se taces core eat Fry See. Fee were iz --Semimembranosus Iliac artery--/ Tliac artery- -f-- nerve @-Semimembranosus nerve -Femoral NERVE as 2 YG i -->-~*-Tibial artery ‘A Saag Tibial nerve ' Peroneal artery A Fiu, 71.—A. Dissection of the Leg of Rana; and B. of Xenopus, from the dorsal surface, showing the veins and arteries and the sciatic nerve. 208 THE FROG—THE PLATANA runs straight across to meet its fellow in the middle line to form the abdominal vein. At the origin of the abdominal vein a small rectal vein is given off to the rectum. In order to expose the pelvic vein clearly, cut through the pelvic girdle on one side and carefully sever the muscles of the leg from the vicinity of the pelvic girdle. | C. Arterial System (part). Distend the cesophagus with cotton-wool or a roll of paper in order to show the blood-vessels clearly, and follow out the anterior part of the arterial system. The two branches of the short ventral aorta or “truncus”’ at once divide into the following three arterial arches :— (a) The carotid arch, which gives off the arteries to the head region. (b) The systemic arch, which curves round the cesophagus. (c) The pulmo-cutaneous arch to the lungs and the skin. Fourth Day Arterial System (continued). 1. Trace the carotid arch, which gives off :— (a) A lingual artery supplying the tongue. (6) A carotid artery supplying the head. It goes round the side of the cesophagus. A slight swelling at its origin is the carotid gland. 2. Trace the systemic arches which curve round the cesophagus, one on each side, towards the dorsal surface of the body. Going backwards and inwards, the two systemics gradually.converge to meet in front of the kidneys, and there unite to form the dorsal aorta. Each systemic arch gives off :— (a) A laryngeal artery to the larynx. (6) An cesophageal artery to the dorsal wall of the cesophagus. (c) An occipito-vertebral artery to the side of the head and the vertebral — column. (d) A subclavian artery to the shoulder and fore-limb. At the point where the dorsal aorta is formed, note the large cceliaco- mesenteric artery which arises there, and which sends branches to the stomach, liver, intestine, and spleen. 2 Trace the dorsal aorta backwards, and note that it passes between the kidneys, there gives off four or six renal arteries, and then divides posteriorly into two iliac arteries which supply the legs. The iliac artery is continued backwards as the sciatic artery in each leg, and divides above the knee into the peroneal and the tibial artery to leg and foot respectively. 3. Trace the pulmo-cutaneous arch, which gives off :— (a) A pulmonary artery along the outer side of the whole length of the lung. (b) A cutaneous artery, which passes forward close behind the ear, and then turns sharply backwards to supply the skin of the back and the sides of the head. 210 THE FROG—THE PLATANA [In the Platana— 1. The carotid arch gives off: (a) Two arteries having a common point of origin near the carotid gland. One supplies the floor of the lower jaw, and may therefore be called the “lingual” artery ; the other supplies the mylo-hyoid muscle. (b) A carotid artery passing to the head. It has, at its origin, a slight swelling, the carotid gland. 2. The systemic arches run backwards on each side of the body, meeting posteriorly to form the dorsal aorta. From each systemic arch an artery arises which has the following branches :— (i) A scapular artery to the pectoral girdle. (ii) A cutaneous artery to the skin. (iii) A brachial artery to the arm. Trace the dorsal aorta backwards, and note that it gives off the caeliaco-mesen- teric artery about midway between its origin and the origin of the first pair of renal arteries. The dorsal aorta then passes between the kidneys, supplying four renal arteries to each kidney, and posteriorly tt divides into two internal iliac arteries to the legs. Each internal iliac gives rise to a branch which divides into : (i) An iliac artery to the muscles round the ilium. (ii) A cutaneous artery to the skin of the body, just anterior to the leg. (iti) A small artery to the dorsal surface of the leg. Carotid gland _Lingual Lingu ye gland fy) ‘Carotid Lett Auricle \° Right Auricle, Left Auricle IN Subclavian aly t -Pulmonary -Ventricle Systemic arch Pulmonary Coeliaco-mesenteric Systemic ‘arch Dorsal aorta Coeliaco-mesenteric ‘Testis Kidney. Renals Cutaneous A. Ws L. A A B Fic. 72.—A. Arterial System of Rana; and B. of Xenopus. 212 THE FROG—THE PLATANA 3. The pulmo-cutaneous arch gives off: (a) A pulmonary artery along the outer side of the whole length of the lung. (b) A cutaneous artery, which at first goes forward to the base of the arm, and then spreads out on the skin of the back of the head. | Make a complete sketch of the arterial system. Remove the heart, taking care to leave attached to it as much as possible of the large vessels. Note the sinus venosus, the conus, the ventral aorta or “‘ truncus arteriosus,” the two auricles, and the ventricle. Slit open the conus, and notice the longitudinal spiral septum (spiral valve). The openings of the conus are guarded by pocket-valves, three at each end. Remove the ventral wall of the two auricles and the ventricle, taking care not to cut away the conus which lies obliquely.across the right auricle. Having washed the blood out of the heart, observe the septum between the right and left auricles, the thick muscular walls and spongy cavity of the ventricle, also the wide auriculo-ventricular opening which is guarded by four valves. In the dorsal wall of the right auricle, near the septum, is the slit-like opening of the sinus venosus with two valves. Near this sinu-auricular aperture, but on the other side of the septum, in the dorsal wall of the left auricle, is the opening of the pulmonary vein from the lungs. Respiratory System and Alimentary System (continued). 1. Remove the mylo-hyoid muscles to expose the hyoid apparatus. Pass a seeker through the glottis to one of the lungs, and slit it open with a pair of scissors. Examine the structure of the lung. Ocsophagus Liver Bile duct Gail bladder Pancreas Stomach, Duodenum* Gall btadder- eum Gees * Entrance of Bile duct: into Duodenum Pyloric constriction! ¥- Rectum Cloacal aperture A B Fic. 73.—A. The Alimentary Canal of Rana ; and B. of Xenopus. 214 THE FROG—THE PLATANA 2. Remove the whole of the alimentary canal, with the liver, pancreas, and spleen, by cutting through the cesophagus and the large intestine (where it joins the cloaca), and detaching it from the roof of the body-cavity without injuring the kidneys and the reproductive organs. Draw the complete alimentary canal. Urino-genital System. Note the kidneys, two elongated flattened dark-red organs lying one on each side of the vertebral column towards the posterior end of the abdominal cavity. From the outer edge of each kidney a duct, the ureter, passes back- wards, and opens into the cloaca on the dorsal side, opposite the opening of the bladder. On the ventral sides of the kidneys the adrenal bodies appear as small yellow patches. [In the Platana these adrenal glands are apparently absent. | In the male Frog note : (a) The testes, a pair of ovoid pale yellow bodies attached to the dorsal wall of the body-cavity by a fold of peritoneum. They lie on the ventral sides of the kidneys and are connected to them by short efferent ducts (vasa efferentia) which pass into the kidneys. Corpora adiposa (Corpora: ~~ adiposa Fic. 74.—A. The Urino-genital System (male) of Rana; and B. of Xenopus. THE FROG—THE PLATANA (b) The corpora adiposa or fatty bodies lying in front of the kidneys. 216 193919)- Bsodipe Bs0dJ0D~~__ aa -sndouay Jo ‘g pue { puny jo (epeurey) woysXg peqiueS-ourmy eyy, “Y—"SL “PLT Vv ---- JNPIAO Joppriq -- ------ Soasie DUSIAO WSIY avsiao Ye} wt ee ee 497019) ------- _. opis 348 jo 2ONPIAO Opis 9] jo ArvagQ esodipt Bsodiory — at POW] onn ce emin we JONPIAO 1481 Jo “>> = > Burmado jeus33u} JONPIAO Yay JO __ AY Buiuado [eus93U] (c) The ureters, which function not only as urinary ducts, but also as vasa 218 THE FROG—THE PLATANA. deferentia for the generative products. See ureter on page 214. Kach ureter has a slight swelling, the vesicula seminalis, on its outer side. [In the Platana the ureters unite posteriorly to form a single duct which opens into the cloaca. ] In the female Frog note : (a) The ovaries, a pair of irregularly-lobed organs, usually consisting of rounded black and white bodies, the ova. The ovaries are attached to the dorsal wall of the body-cavity by a fold of the peritoneum. (b) The corpora adiposa lying in front of the kidneys. (c) The long convoluted oviducts opening in front into the body-cavity and behind into the cloaca. Their terminal portions are greatly dilated ovisacs in which the eggs are retained for a time. [In the female Platana the ureters open separately into the cloaca. | Make a drawing of the urino-genital system. Fifth Day Skeletal System (continued). A. The Pectoral and Pelvic Girdles and the Limbs. 1. Detach a fore-limb with the remaining parts of the pectoral girdle. Make a preparation showing : Supra-scapula, scapula, remainders of the clavicle and the coracoid, humerus, radio-ulna, carpal bones, and digits. Draw these parts. Supra scapul: Episternum_ ip! la, + I Omosternum Supra soapy a Clavicle cae : r Scapula . Scapula i Coracoid-” Epicoracoid” Paaes aan ‘Sternum Epicoracoid-- | Metasternum 3 -Xiphister num Metasternum- A B Fic. 76.—A. Pectoral Girdle of Rana; and B. of Xenopus. The dotted portions indicate cartilage. 2. Detach the pelvic girdle from the transverse processes of the 9th vertebra. Remove it along with the hind-limbs from the body. Detach the limb from one side of the pelvic girdle, and make a sketch showing the following parts of the pelvic girdle :— Acetabulum or socket for head of femur, ilium, ischium, and pubis. (See Fig. 79.) Acetabulum Hivm CO Ischium lium Acetabulum ‘ lactam Pubis A B Fic. 77.—A. Pelvic Girdle of Rana; and B. of Xenopus, side view. 220 THE FROG—THE PLATANA _ 8. Make a preparation and a sketch of the hind-limb showing the femur, tibio-fibula, astragalus, caleaneum or os calcis, and the other bones of the tarsal region, five meta-tarsals, and digits. Number-the digits from the inner side. Femur Supra scapula : Scepuia i Tibia-fibula--} 4 R Radio-ulna Fie. 78.—The Hind-limb and the Fore-limb of Xenopus. B. The Vertebral Column. 1. Remove the skin and muscles from the dorsal surface of the back to show the nine vertebre and the urostyle. Make a drawing showing the vertebre with their transverse processes, and the urostyle attached to the posterior end of the 9th vertebra. ; The 2nd to the 9th vertebre bear long transverse processes produced outwards. The urostyle is attached to the 9th vertebra by two facets. [In the Platana the 2nd, 3rd, and 4th vertebre bear long transverse processes curved backwards, those of the 3rd and 4th being tipped with small cartilaginous ribs. The transverse processes of the 5th, 6th, 7th, and 8th vertebre are slender and project forwards and outwards. The 9th vertebra has long wing-like processes, attached to which are the ilia of the pelvic girdle. The urostyle is fused to the 9th vertebra. | Note the intervertebral discs and the intervertebral foramina for the exit of the nerves from the spinal cord. 2. Remove, examine, and draw the Ist or atlas vertebra, noting its ring- like form, the absence of transverse processes, and the concave facets by which it articulates with the two occipital condyles of the skull. 3. Remove, examine, and draw the 8rd vertebra, noting the proccelous! centrum, neural arch and neural spine, anterior and posterior zygapophyses, and the transverse processes. [The centrum is opisthocelous” in the Platana, and each transverse process bears a cartilaginous rib. ] 1 Proccelous means concave in front and convex behind. 2 Opisthoccelous means convex in front and concave behind. 222 THE FROG—THE PLATANA _--Transverse process of 9th vertebra---~~ #----Ischium Ischium- -- A’ B Fic. 79.—A. The Vertebral Column and Pelvic Girdle of Rana; and B. of Xenopus. 4. Remove and examine the 8th vertebra, and note that the centrum is amphiccelous.!. Make a drawing of a section showing the centrum. [The centrum is opisthocelous in the Platana. | 5. Remove and examine the 9th vertebra or sacrum, and note that the centrum is slightly convex on its anterior surface. The urostyle articulates with the two convex facets on the posterior surface of the 9th vertebra. It is a rod-like bone gradually tapering to a point. [In the Platana the urostyle is fused to the posterior surface of the 9th vertebra, and the transverse processes are long, flat, and wing-like. | Siath Day Skeletal System (continued). C. The Skull. 1. Remove the skin and other tissues from the top of the skull and ob- serve the large fronto-parietals, sphenethmoid, nasals, premaxille, maxille, 1 Amphiccelous means concave at both ends. 224 THE FROG—THE PLATANA squamosals, exoccipitals and pro-otics. The quadrato-jugals are well developed ; but the quadrate consists of a piece of cartilage at the posterior end of the quadrato-jugal, between the pterygoid and the squamosal. The lower jaw articulates with the quadrate cartilages. The columella is usually not well shown. Between the various bones of the skull there are considerable areas of unossified cartilage. persistent parts of the original chondrocranium. Premaxilla Premaxilla iN Septomaxillary <7 Maxilla . -Sphenethmoid Squamosal-. /f Columelia fi 1 sis a i . Pro-otic Praoccipital : t to7 Poramen magauni iP. ' Occipital condyle Foramen magnum A B Fie. 80.—A. Dorsal View of the Skull of Rana; and B. of Xenopus [In the Platana the fronto-parietals, nasals, supra-ethmoid, premaville, mawille, squamosals, exoccipitals, and pro-otics are well shown. The quadrato- jugals are very inconspicuous. An ewtrastapedial plate of cartilage is weil developed, and the bony columella may be seen lying underneath it. . The sides of the skull consist of bones which represent the orbitosphenoids and alisphenoids of higher types. The supra-occipital is represented by a small cartilage. | Make a drawing of the dorsal aspect of the skull. Premaxilla Premaxilla Quadrate- iy Quadrato-jugal Occipital condyle ' Basioccipital A B Fic. 81.—A. Ventral View of the Skull of Rana; and B. of Xenopus. 226 THE FROG—THE PLATANA 2. Remove the skin from the roof of the mouth and note the parasphenoid, a large L-shaped bone occupying the ventral surface of the cranium, the paired vomers bearing the vomerine teeth, the premaxille, the maxille, the slender palatines, the triradiate pterygoids, the squamosals lying under the pterygoids, the quadrato-jugals, the pro-otics, and the exoccipitals. (See Fig. 81, page 224.) [In the Platana there is only one vomer. The pterygoids are large and have leaf- like processes, which are produced towards the middle line, and which cover the Eustachian passages. There are two well-developed quadrates for the articulation of the lower jaw ; and there is a basioccipital, composed of cartilage. The orbito- sphenoid and the alisphenoid are well marked. The palatines are absent. | Make a drawing of the ventral aspect of the skull. 3. Make a drawing of the skull viewed from the side to show the premaxilla, maxilla, quadrato-jugal, nasal, sphenethmoid, fronto-parietal, pterygoid, squamosal, and pro-otic. [In the Platana the supra-ethmoid, orbitosphenoid, alisphenoid, extrastapedial, and columella may be noted in addition. | Farasphenoid Alisphenoid Fronto-parietal af Pro-otic \ Fronto-parietal “ . ‘ ‘ . ' Provotie Sphenethmoid \, smlemnmome!;,_ Orbitosphénoid ; Ps ss a rep! Supraethmoid . . ‘ Premaxilla = of y \ Maxilla Nasal Columella +” pterygoid Squamosal gP