^> VIC*.' _ 5 i^S'-SCfc Ccec 1 \ ■' «5-sr, ■'■<<: < i ^ rn NORTH AMERICAN LAND BIRDS Charles A. Kkeler. San Francisco: California Academy of Sciences, January, 1893. Committee oj Puhlication: H. W. HARKNESS, H. H. BEHR, T. S. BRANUEGEH- Editor : TowNSHENn Stith Bkandf.gkk. PEEFACE. The present paper has been written more with the hope of stimulating thought and inciting research in a new and as yet almost untrodden field of ornithological inquiry, than with the expectation of reaching definite results. The subject is as yet too new and difficult to be reduced to even the semblance of an exact science, and accordingly all the views here set forth are more or less provisional and tentative. I have constantly pro- ceeded upon the assumption that a poor theory is better than no theory, provided it be not considered as final, since it affords an opening wedge for the further study of a subject. Accordingly many of the views here set forth are hardly to be considered as more than guesses, and it is expected that future study will serve to show their fallacy. If they lead to this further study, however, and to more exact and comprehensive work by others, I shall be glad to see them overturned and their places filled by more worthy hypotheses. In the preparation of the work I have received much valuable assistance, which I here take pleasure in ac- knjDwledging. Much of the examination of specimens was done at the United States National Museum, the authorities of which kindly placed their collection of birds at my disposal. To Mr. Eobert Ridgwayl am in- debted for innumerable personal favors during my stay in Washington. His Manual of North American Birds has formed the systematic basis for this paper. Dr. L. VI PREFACE. Stejneger assisted me very materially by his criticism and suggestions, he having devoted more attention to this subject than any other American ornithologist. Dr. Elliott Coues furnished me with several useful terms (some of them new), as well as many suggestions which have been of value. Mr. F. C. Test of Washington, Mr. Witmer Stone of the Philadelphia Academy of Sciences, and Dr. J. A. Allen and Mr. Frank M. Chapman of the American Museum of Natural History, have aided my work, both by placing their collections at my disposal and by furnishing me with valuable facts and sugges- tions. Dr. Allen's important contributions to the sub- ject here discussed have been of far more service than the mere quotations indicate. To Mrs. Katharine Bran- degee and Mr. Frank H. Vaslit I desire to return thanks for their kind and painstaking revision of the proof, also to Mr. Walter E. Bryant, who read the proof for scientific terminology. Berkeley, Cal., December 21, 1892. C. A. K. CONTENTS OUTLINE. INTRODUCTION. THE INHEBITANCE OP ACQUIRED CHARAOTEKS 2 Theoretical Aspect of the Subject 2 Heredity. Introduction; 2; Lamarck, originator of the doctrine of use and disuse, 2; Hilaire, originator of the doctrine of environ- mental influences, 2-3; Darwin, doctrine of pangenesis, 3; Brooks and Galton's modifications of this, 5; Morgan, criticism of pan- genesis, 5; Spencer, physiological units, 6; bearing of theories of heredity upon transmission of acquired characters, 7; Weis- mann, 7; value of his work, 8; immortality of protozoa, 8; mor- tality of jnetazoa, 9; Naegeli's nucleoplasm theory criticised, 10; immortality of germplasm precluding the inheritance of acquired characters, 10; Vines' criticism of Weismann, 11; Weismann's reply to Vines, 13; Ryder, theory of heredity opposed to Weis- mann, 17; Morgan on cellular continuity, 19; Eimer on same, 20; summary of argument between Weismann and his opponents, 21. Pammixis. Morgan's criticism of, 22; Cunningham's criticism, 23; Romanes on cessation of selection, 23; other theories to account for degeneration, reversal of selection (Romanes), economy of energy (Darwin), disuse (Lamarck), retardation (Cope), 24. Practical Aspect of the Subject 27 Consequences of Dispensing with the Inheritance of Acquired Characters. Cunningham, general consequences, 27; inability of accounting for origination of new characters, 27; inheritance of acquired characters by protozoa admitted, 28; Osborn, why should this factor become obsolete?, 28; Romanes, all variations must be. directly acquired, 28. Evidence of Observed Cases of Transmission. Abnormal Trans- missions. Cunningham on why mutilations are not transmitted, 29; Morgan, the transmission of mutilations not a proof of the inheritance of acquired characters, 29; Weismann on mutila- tions, 30; experiments with white mice, 31; Cunningham's criti- cism of his observations on the feet of Chinese ladies, 31; Eimer, instances of observed oases of transmission of mutilations, 32-34; inheritance of artificially induced epilepsy in guinea pigs, 34. Vlll CALIFORNIA ACADEMY OF SCIENCES. Normal Transmissions: observed instances of change due to enyiron- ment, 34; examples of changes in goldfish and brine-shrimp, 34-35; discussion of the validity of these examples as proofs, 35; after effects in plants illustrative of an hereditary rhythm, 36; change in environment not established in one generation, but only the predisposition to change, 37; inheritance of acquired habits, 38; Elliott's examples, 38; these not proofs of inheritance, 39; Dar- win's instances criticised by Ball, 40; results which can be best explained by transmission of acquired characters, 41; Romanes' examples of instinct due to the transmission of acquired charac- ters, 41-42; aesthetic faculties of man, 42; Spencer's three forms of evidence of transmission, 43; the first and third form untenable, according to Romanes and Ball, 43-44; correlation as a proof, 44; the giraffe as an illustration of correlation, 44; Ball's criticism of this illustration, 45; further discussion of correlation, 46; Osborn on paleontological proofs of transmission, 46-48; Poulton's reply to Osborn's evidencs, 48; summary of discussion, 49-50. TAEIATION AND NATURAL SELECTION 50 Scope and meaning of natural selection, 51; not creative (Schur- man), 51; conditioned by variation, 52; variations quantitative rather than qualitative, 52; how are new parts originated?, 53; variations must be advantageous to be favored by selection, 53; Romanes on useless variations favored by selection, 54. Theoeies Explaining Variation 54 Spencer's physiological units, 55; Weismann on sexual combina- tions, 55; variations according to this viewmust be within the ex- tremes of ancestral modification, 55; Hartog's objection, 56; Lloyd Morgan's theory of organic compounds, 58; objections to this view, 59; Three views of the origin of variations, 59; spontaneous, uninfluenced by environment, 59; due solely to environment, 60; inherent tendency to vary in a specific direction, 60; conservative variations, 61; progressive variations, 61; Brooks' secondary laws of variation, 62; conclusion concerning variations, 62. LAWS CONDITIONING EVOLUTION 64 Laws of Development 65 Bathmism, or growth force, 65; law of extent and density; 66; phylogenic extent and density, 67; metabolism, 67; law of sexual intensification, 68; Gulick's criticism of Brooks' theory of male progressiveness, 72; acceleration and retardation, 73; cause of ac- celeration, 74; the originator of the fittest, 75; bearing of the law of phylogenic extent and density upon acceleration and retardation, 76; law of concentration, 77. Laws of Structcjbe 77 Homology, 77; successional relation, 77; parallelism, 78; adapta- tion, 78; geratology, 78; bilateral symmetry, 79; correlation of growth, 79. CONTENTS OUTLINE. IX Laws of Heredity 79 Uninterrupted or continuous transmission, 79; interrupted or latent transmission, 79; sexual transmission, 79; mixed or mutual transmission, 79; abridged or simplified transmission, 80. SEXUAL SELECTION 80 Law of battle, 81; preferential mating, 81; Darwin's and Wallace's views compared, 82; relation of color of male to vitality and vigor, 82; color as related to integumentary expanse and complexity, 83. Evidence of Selection by the Female 84 Peckham on sexual selection among spiders, 84; Wallace's ex- planation of sexual display by male birds, 85; the house-finch as an illustration of selection, 86; objection that each bird finds a mate, 87. Difficulties in the Theory of Sexual Selection and Alternative Hypotheses 88 Beddard on sexual dichromatism without selection, 89; difficulty of believing in a highly developed sesthetio sense in birds, 90; Stolzman's view of bright colors and appendages of male birds, 91; Eomanes' reply to Wallace's objections, 92; Wallace on the iesthetio sense in relation to sexual selection, 93; Poulton on the same, 94; Morgan on the testhetio taste of birds, 95; the beautiful in inorganic nature contrasted with the beauty of birds and in- sects, 96; Weismann on novelty as the cause of sexual selection, 97; Romanes on the beautiful among the lower forms of life, 97; coloration viewed from a general standpoint, 98; colors which have been evolved with reference to some percipient being, 99; implications of the theory of sexual selection, 100; Grant Allen on the mechanical explanation of the pleasure derived from color combinations, 100; the pleasure given to birds by color combina- tions is of this lower order, 101; synthesis of factors involved in the production of the sexual character of birds, 102. THE NATURE OF SPECIES 103 On iteE Meaning and Limitations of the Term 103 Natural and artificial modes of classification, 103; the basis of a natural system, 103; relativity of the term species, 104; definition of species as used in science, 105. On the Relation of Evolution to Species 106 Species necessary for rationality in evolutionary progression, 106; Romanes on the preservation of the species by natural selection, 106; objections to Romanes' view, 107; reproduction as growth beyond the individual as an explanation of the origination of altruistic characters and traits, 108; necessity for natural selection to preserve family, and in some instances the tribe, but not the species, 109. X CALIFORNIA ACADEMY OF SCIENCES. ISOLATION AS A FACTOR IN THE EVOLUTION OF SPECIES. 110 Physiological Selection 110 Eomanes' three diflSculties in natural selection considered as a theory of the origin of species, 110; explanation of physiological selection, 111; sterility of species. 111; variations in the repro- ductive system as correlated with other variations, 113; on the swamping effects of interbreeding and the inutility of specific characters, 114; objections to physiological selection by Meldola and Galton, 115; Eomanes' reply to these objeotions, 116; Wal- lace's objections, 117; Eomanes' reply to Wallace, 118; Seebohm's criticisms, 121; Eomanes' answer, 122; Dyer's criticisms, and Eomanes' refutation of his objections, 123; conclusions concern- physiological selection, 124. Gtjlick on Isolation 125 Eesemblance and difference between the view of Eomanes and Gulick, 125; criticism of his views, as ignoring the origin of varia- tions, 126; necessity for isolation established, 127; forms of isola- tion, 128 et seq. II. THE COLORS OF NORTH AMERICAN BIRDS. ON MODES OF PLUMAGE CHANGES 132 By the feather itself becoming altered in color, 133; by the wear- ing off of the lengthened lighter-colored tips of the feather, 135; classification of different modes of plumage change, 137. GENEEAL PEINCIPLES OF COLOE IN BIEDS 137 On the physical and mechanical causes of color effects, 137; state- ment of the theory of bird colors to be elaborated, 139; law of as- sortment of pigments, 140; examples illustrating this law, 140; on generalized and specialized colors, 142. THE PROPOETION AND DISTEIBUTION OF THE COLOES IN NOETH AMEEICAN GENERA 143 On the general distribution of the fundamental colors among North American genera, 143; the bearing of these facts on the law of the assortment of pigments, 145; the proportion and distribu- tion of black, 146; white, 151; black and white as cognate colors, 152; the proportion and distribution of red, 153; red and yellow as correlative colors, 154; examples showing this interdependence, 155; the proportion and distribution of yellow, 157; blue, 157; generalizations from foregoing facts, 158. THE PATTEEN OF MAEKINGS 159 On Individual Feathers 159 Feather markings as affected by the general laws of growth, 159; Eimer and Kerachner on feather markings, 162; secondary pig- CONTENTS OUTLINE. XI mentation to be aoodurited foi'by metabolism, 163; examples illus- trating the ' method , of pigment ass-umptiou, 163; su'coessional taxology, 164; further examples of successional taxology, 164; study of the pattern of markings on the wing of Falco sparverius, 165; the significance of successional taxology, 169; natural selec- tion as a factor in the origination of feather marks; 170; repeti- tive Eiarks, 171; hybrid feathers, 172; examples of hybrid feathers, 173; classification of the different forms of hybrid feat hers, 174; explanation of the different forms of hybrid feathers, 174; pseudo- hybrids, 177. ' ' On the General Patterns oe BirC Colors '. ; . . 179 Elmer's law of posterior-anterior progression of markings, 179; markings of the primitive plumage, 180; characteristic types of markings, and those which seldom or never occur, 180; Dr. Har- rison Allen on the relation between large masses of muscular and nervous tissue and color patches, 182; on the location of color patches on the most conspicuous pa^rts of the body, 183; the superciliary stripe, 185; on the markings of the head, ' 186; rela- tion between laws of growth and selection in the production of these markings, 190; wing markings, 190; tail' markings, 191. Recognition Marks 193 Markings considered from the Standpoint of their utility, 193; Poulton's classification on this basis, 194; protective colors (pro- cryptic), 195; aggressive colors (anticryptic), 197;' false warning colors (pseudosematic), 198; warning colors (aposematic), 200; recognition marks proper (episematic), 200; Wallace on recogni- tion marks, 200; Todd on directive colors, 201; classification of recognition markings, 201; recognition at a distance and at close range, 203; recognition markings among the grouse, pigeons and hawks, 204; tail markings of the Caprimulgidae, 207; law of sexual recognition, 209; socialistic markings, 210. VAEIATION OP COLOK WITH SEX, AGE AND SEASON 211 Individual variation in bird markings, 211; epigainic colors, 211; Darwin's classification of birds according to the variations in plumage with sex, age, and season, 212; additional classes, 213; revised table of classification, 214; male like female, young like adult, 214; male like female, young differ from adult, 216; re- semblance of sexes differing with the seasons, or both sexes alike and varying with the seasons, 218; male more conspicuously colored, young like female, 221; male more conspicuously col- ored, young witb peculiar first plumage, 222; male more con- spicuously colored, young of each sex resembles its respective adult, 223; adult male more conspicuously colored, young male unlike adults of either sex, 224. XU CALIFORNIA ACADEMY OP SCIENCES. THE DIRECT INFLUENCES OF THE ENVIRONMENT 225 Beddard on the general effects of food on color, 226; Stejneger's theory of melanism and albinism, 226; Sauermann's experiments in changing color by food, 227; influence of temperature, moist- ure and sunlight on food, 229; instances where intensifying and bleaching has been the result of the presence or absence of sun- light, 230; Garman on the bleaching power of sunlight, 231; ob- jections to Garman's theory, 231; pale colors of the under parts of animals due to the absence of sunlight, 232; reconciliation of this Tiew with the bleaching effect of sunlight, 233. GEOGRAPHICAL DISTRIBUTION AS A FACTOR IN THE EVOLUTION OF COLORS 234 General survey of the f aunal areas of North America, in their relation to extralimital faunas, 234; birds of the Boreal area, 235; absence of brilliantly colored genera among boreal forms, 236; reasons for this lack of specialization among northern forms, 237; brilliancy of tropical species, 238; Beddard on special relations of color to geographical distribution, 238; on the resemblance of the colors of Sturnella and Macronyx, 239; Ridgway on the relation between color and geographical distribution, 241; Spinus psallria as an instance of melanism as related to distribution, 241; other ex- amples of melanism toward the south, 243; intensification in yellow toward the tropics, 243; intensification of red with change in climate, 244; increase in blue from north to south, 245; Cyano- citta stelleri studied with reference to the connection between color marks and geographical distribution, 245; J. A. Allen on the relation between climate and geographical races, 247; Melospiza fasciaia as an instance of the result of climatic influence, 248; the ice age as a factor in isolation, 249; examples of forms produced by an east and west isolation, 250; examples of north and south isolation, 252; varieties or closely related species whose ranges overlap, 253; particular instances where the different races cannot have been produced solely by climatic influences, 255; Myiarchus as an example of species which have been produced by climatic influences alone, 256. ORDERS, FAMILIES, AND GENERA OF NORTH AMERICAN BIRDS, CONSIDERED FROM THE STANDPOINT OF THEIR EVGLUTION 257 BIBLIOGRAPHY 337 EXPLANATION OF PLATES 345 INDEX , 349 THE EVOLUTION OF THE COLORS OF NORTH AMER- ICAN LAND BIRDS. I. Introduction. A few words of explanation may be said with regard to the greatly disproportionate length of the introductory portion of this work. To the uninitiated the most perfect harmony is commonly thought to prevail concerning the great problems of evolutionary philosophy, but once within the circle of current scientific thought and the reverse is found to be true. Instead of harmony, discord is discovered. There is hardly one of the important doctrines concerning which a consensus of scientific opinion has been attained. To be sure, all maintain that Darwinism or natural selection is a factor in evolution, but while some hold it to be the only factor, and all-suffi- cient in the creation of species, others believe it to be a very minor agency, and relegate it to the post of inspec- tor-general of the army of life. With regard to sexual se- lection the same diversity of opinion prevails, one school advocating sexual selection as the sole agent in produc- ing the brilliant colors and varied plumes of male birds, etc., the other extreme asserting that sexual selection as a factor in evolution is a myth. Still greater is the di- versity of opinion and more intense the feeling in regard to that momentous question which is at present agitating the troubled sea of scientific thought — the transmission of acquired character. In view of all this disagreement, it is quite impossible to undertake any general scientific investigations in the field of evolution without a tolerably thorough survey of the whole ground. With this end in view, and merely as a preparation for the more particular investigations of the work, these preliminary pages have been written. The tenability* of the theories here advanced need not J CALIFORNIA ACADEMY QF SCIENCES. materially affect the work of the second part, although the theories concerning the special investigations in the evolution of color in birds are largely founded upon the principles laid down in Part I. Although this first part is necessarily of a general character, nothing has been inserted which has not some bearing upon the investiga- tions which follow. An attempt has been made to dis- cuss the general principles of evolution according to a logical system, the subject of the inheritance of acquired characters being treated first, as it is the most funda- mental question in dispute. The doctrine of evolution is by no means modern in its conception, having been dimly foreshadowed from the days of Aristotle; but it was first suggested in a plausible scientific form by Jean Lamarck, who, in 1809, published his Philosopliie Zoologique. He attempted to account for the changes in organic forms almost ex- clusively by the principles of the use and disuse of parts of which doctrine he was the originator. His views were hardly noticed at the time they were announced, but a little later Geoffrey St. Hilaire was more successful in calling the attention of the scientific world to his own closely related theory of the action of the environment in producing the changes in organic beings; although his views were not generally accepted by the naturalists of the day The nature and extent of his theory is ex- plained in the following Avords of Haeckel.* " He con- ceives the organism as passive, in regard to the vital conditions of the outer world, while Lamarck, on the contrary, regards it as active. Geoffroy thinks, for ex- ample, that birds originated from lizard-like reptiles, simply by a diminution of the carbonic acid in the at- mosphere, in consequence of which the breathing pro- •"Historj' of Creation, I., p. 117. EVOLUTION OF THE COLORS OF BIRDS. 3 cess became more animated and energetic through the increased proportion of oxygen in the atmosphere. Thus there arose a higher temperature of the blood, an in- creased activity of the nerves and muscles, and the scales of the reptiles became the feathers of birds," etc. The principle of use and disuse, and the transmission of acquired characters, are very closely related and stand or fall together. Darwin, in his Origin of Species, and throughout all his subsequent writings, accepted them both as supplementary to his own doctrine of natural selec- tion, in accounting for the origin of species. It was, of course, generally admitted that an individual could, dur- ing the course of its life, acquire characters peculiar to itself, or could modify its parts by use or disuse. More- over, it was commonly held that such modifications could be transmitted by the individual to its offspring. To this view Darwin was committed, and in order to ex- plain it in a rational way he formulated the provisional hypothesis of pangenesis, which he describes in the fol- lowing language: " This important distinction between transmission and development will be best kept in mind by the aid of the hypothesis of pangenesis. According to this hypothesis, every unit or cell of the body throws off gemmules or undeveloped atoms, which are trans- mitted to the offspring of both sexes, and are multiplied by self division. They may remain undeveloped dur- ing the early years of life or during successive genera- tions; and their development into units or cells, like those from which they were derived, depends on their •afTmity for, and union with other units or cells pre- viously developed in the due order of growth."* Mr. Eomanes has presented Darwin's hypothesis of pangenesis! in so able and comprehensive a manner *Descent of Man, p. 228. tWeismann's Theory of Heredity by George J. Bomanes. Contempo- rary Eeview. May 1890, pp. 686-699. 4 CALIFORNIA ACADEMY OF SCIENCES. that in order to convey a proper understanding of the subject I cannot do better than r^uote his words in full. It is stated in the following seven assumptions: " 1 . That all the component cells of a multicellular or- ganism throw off inconceivably minute germs or "gem- mules," which are then dispersed throughout the whole system. 2. That these gemmules, when so dispersed and sup- plied with proper nutriment, multiply by self division, and, under suitable conditions, are capable of develop- ing into physiological cells like those from which they were originally and severally derived. 3. That while still in this gemmular condition, these cell seeds have one for another a mutual affinity, which leads to their being collected from all parts of the system by the reproductive glands of the organism; and that, when so collected, they go to constitute the essential material of the sexual elements — ova and spermatozoa being thus nothing inore than aggregated packets of gemmules, which have emanated from all the cells of all the tissues of the organism. 4. That the development of a new organism, out of the fusion of two such packets of gemmules, is due to a summation of all the developments of some of the gem- mules which those two packets contain. 5. That a large proportional number of the gemmules in each packet, however, fail to develop, and are then transmitted in a dormant state to future generations, in any of which they may be developed subsequently — thus giving rise to the phenomena of reversion or atavism. 6. That in all cases the development of gemmules into the form of their parent cells depends on their suit- able union with other partially developed gemmules, which precede them in tlie regular course of their growth. EVOLUTION OF THE COLORS OF BIRDS. 5 7. That gemmules are thrown off by all physiolog- ical cells, not only during the adult state of the organ- ism, but during all stages of development. Or, in other words, that the production of these cell-seeds depends upon the adult condition of parent cells; not upon that of the multicellular organism." This theory has subsequently been varied in its details by Brooks, Galton, Herdman, and others. According to Brooks the ovary is passive and does not aid in the transmission of acquired characters, but the sperm cells contain gemmules which are thrown off from such parts as are undergoing change. Galton believed to a con- siderable degree in the continuity of the germ plasm, although also holding that acquired characters are in- heritable. For example, he says, " From the well- known circumstance that an individual may transmit to his descendents ancestral qualities which he does not himself possess, we are assured that they could not have been altogether destroyed in him, but must have main- tained their existence in a latent form. Therefore each individual may properly be considered as consisting of two parts, one of which is latent and only known to us by its effects on his posterity, while the other is patent, and constitutes the person manifest to our senses."* These latent characters he considered to be transmitted from generation to generation by means of a portion of the gemmules of the fertilized ovum which remained unde- veloped. Although at first adopting an hypothesis of pangenesis he afterwards abandoned this for a theory of the continuity of the germ-plasm not unlike that of Weismann. Lloyd Morgan criticises the pangenetic hypothesis in the following well chosen words: "The existence of 'On Blood Uelationship, Proc. Eoy. Soc, 1872, p. 394. b CALIFORNIA ACADEMY OF SCIENCES. gemmules, then, is unproven, and their supposed mode of origin not in altogether satisfactory accordance with organic analogies. Furthermore, the whole machinery of the scheme of heredity is complicated and hyper- hypothetical. It is difficult to read Darwin's account of reversion, the inheritance of functionally acquired char- acters and the non-inheritance of mutilation, or to fol- low his skillful manipulation of the invisible army of gemmules, without being tempted to exclaim — What cannot be explained, if this be explanation? and to ask whether an honest confession of ignorance, of which we are all so terribly afraid, be not, after all, a more satis- factory position."* Haeckel's plastidule theory and Spencer's theory of physiological units do not differ very essentially from Darwin's hypothesis of pangenesis, although Spencer's idea is a much less crude one. He finds that the units of which an organism is composed have the property of arranging themselves in a definite form or sequence, and then proceeds to enquire into the nature of these units. He first shows tliat they cannot be chemical, for the chemical composition of the various organic bodies which arrange themselves in such diverse shapes is essentially alike in all cases. Neither can morphologi- cal units be accepted as final. The simple cell is the morphological unit, but certain tissues arise directly out of the formative substance without the intervention of a cellular stage. Moreover, certain non-cellular or- ganisms, such as Rhizopods, are capable of transmitting peculiar specific characters. From these exceptions it is evident that this formative power does not reside in cells; and consequently both chemical and morphologi- cal units are disposed of. Spencer then argues for 'Animal Life and Intelligence, p. 137. EVOLUTION OP THE COLORS OF BIRDS. 7 physiological units in the following terms:* "If, then, this organic polarity can be possessed neither by the chemical units nor the morphological units, we must conceive it as possessed by certain intermediate units, which we may term physiological. There seems no alter- native but to suppose, that the chemical units combine into units immensely more complex than themselves, complex as they are; and that in each organism, the physiological units produced by this further compound- ing of highly compound atoms, have a more or less dis- tinctive character." Before considering the subject of heredity in further detail, it may be well to pause a moment to consider its bearing upon the question in hand — the inheritance of acquired characters. Obviously the nature of the me- chanical process by which heredity is made possible must most decisively determine what the possibilities of heredity are — just what characters can be inherited, and what characters cannot (if any such exist). Darwin be- gan with the assumption that all characters could be in- herited and framed his theory of heredity upon this assumption. In this he was followed by the various subsequent writers on the subject, with the exception of Spencer, whose theory does not appear to be designed with the express view of accounting for the inheritance of acquired characters, but rather to have been con- structed inductively. Such was the state of the case when, in 1885, Mr. A. E. Shipley in an article in " The Nineteenth Century," called the attention of English and American scientists to the views of Prof. August Weismann, of Freiburg. Since then two editions of an English translation of the collected essays of Prof. Weismann on the subject of •Principles of Biology, I, 183. '^ CALIFOKNIA ACADEMY OP SCIENCES. lieredily have appeared, the second in 1891. Pi'of. Weismann's views, although not entirely original, are stated with such a rigid consistency to all the conse- (luencus which they involve, are fraught with such un- usual and daring speculations, and so vitally affect many of our scientific dogmas, that they have caused a re- markable revolution in the scientific world. By many English biologists these new views have been received with great favor. Wallace has thrown the weight of his api)roval with them. With such avidity have they been accepted that one is almost tempted to feel that a reac- tion must ultimately follow. In America the case has been directly the reverse. Instead of meeting with favor they have been passed by in silence, questioned, doubted, denied, and even in some cases treated almost with scorn and ridicule. Against such an extreme as this also, reaction seems inevitable. The chief value of ^\''eismann's work, regardless of how correct or incorrect it iiiay ultimately prove to be, is the fact that he has attacked the problem of heredity from an entirely new point of view, and has set the sci- entific world to thinking. It will be advisable to con- sider his speculations in some detail, as bearing directly upon the subject under discussion. Weismann commences his discussion with an inquiry into the nature of death. He asks why mortality should be a necessary consequence of life. In unicellular organ- isms reproduction takes place by fission. The life of one umceba cojiies to an end by the division of the parent into two equal halves, each of which forms a new individual. " But," as Weismann says, " this process cannot be truly called death, ^\"here is the dead body? — what is it that dies? Nothing dies ; the body of the animal only divides into two similar parts, possessing the same constitution. Each of these parts is exactly like its parent, lives in the EVOLUTION OF THE COLORS OF BIRDS. 9 same manner, and finally also divides into two halves. As far as these organisms are concerned, death can only be spoken of in the most figurative sense."* From this view of Weismann's in regard to the immortality of pro- tozoa there has been but 1-ittle dissent. The most seri- ous objection that has been raised to it is that of Maupas, who has shown that even among amoeba conjunction is occasionally necessary to effect rejuvenescence, and who holds that, in consequence of this, even unicellular or- ganisms are mortal. Geddes and Thomson have well stated,! however, that Maupas' experiments, instead of being contradictory to Weismann's view, should be in- serted as a saving clause, for in a state of nature this rejuvenescence by coalescence does take place when needed and neither the organism as a whole nor any part of it dies. Having established the immortality of unicellular or- ganisms, Weismann attempts to account for the intro- duction of death into the economy of nature on the principle of the advantage to the race as a whole, of the sacrifice of the old and decrepit to the young and vig- orous. The weaknesses and fallacies of this part of his theory have been pointed out with especial force by Lloyd Morgan, t The fact seems to be tolerablj^ well established that in protozoa death never normally ends the career of the organism, although of course violent death by accident is perfectly possible, while in metazoa death is the nat- ural outcome. Or, as Weismann explains it, there is no limit to the number of times an amoeban cell can divide itself, but the cells of a more complex organism are lim- * Essays upon Heredity, 1891, I, p. 26. tEvohitioii of Sex, Humboldt Library, p. 240. JAnimal Life and Intelligence, pp. 184 and 193. 10 CALIFORNIA ACADEMY OP SCIENCES. ited in their powers of reproduction and ultimately wear out. To this latter rule Weismann makes one important exception, viz: the germ cells. In the case of some in- sects and other invertebrates it has been demonstated that almost at the commencement of embryonic devel- opment the reproductive cells are set apart. In the case of these organisms it is evident that there is an immor- tal chain of reproductive cells from one generation to another. Observation has proved, however, that it is only in rarely exceptional cases that the reproductive cells are thus set apart, and that in ordinary metazoa they appear after the embryo is well advanced toward maturity. Weismann argues very reasonably that it is at variance with the laws of development to assume, as Nsegeli does, the existence of a nucleoplasm which first develops into the more complex body cells and then be- comes simplified into reproductive cells; and he accord- ingly substitutes an hypothesis of his own. He assumes the existence of germ-plasm intermingled with the body plasm and capable of producing the latter, although body plasm cannot be converted into germ-plasm. There is, then, in the higher metazoa, not an immortal chain of reproductive cells, but an immortal chain of germ-plasms. From this standpoint the heredity of acquired char- acters is obviously impossible. The germ-plasm cannot be influenced by the body plasm. The hypothesis, from its very nature places an effectual barrier against the in- heritance of acquired characters, and in case it could be demonstrated as true, it would be necessary to explain all such supposed cases of transmission in some other way. This is what Weismann and his followers have done, but before considering the evidence for and against such transmission of acquired characters, it will be ad- visable to consider how well founded this theory is. EVOLUTION OF THE COLORS OF BIRDS. 11 Prof. S. H. Vines has criticised it in an article enti- tled "An Exaixiination of Some Points in Prof. Weis- mann's Theory of Heredity," which appeared in Nature, October 24, 1889 (pp. 621-626). Prof. Vines admits the immortality of protozoa, but questions the explanation of Prof. Weismann as to how the immortal protozoa evolved into the mortal metazoa. He objects to Weis- mann's suggestion of unequal fission as being no ex- planation, and asserts that if unequal fission were the cause it would be necessary to assume that a potential mortality already existed in protozoa. "It is impossible to conceive," he says, "that unequal fission can take place in a cell consisting throughout of essentially the same kind of substance." Furthermore, as Prof. Vines points out, Weismann claims that the germ-plasm is located chiefly in the nucleus of the germ-cell, but does not explain of what the remaining portion of the germ- cell consists. Obviously it must be somatoplasm, which is mortal, despite the fact that Weismann has asserted that the entire germ-cell is immortal. Prof. Vines suggests as an explanation of the paradox, " the assump- tion that the substance of the nucleus determines the nature and character of the cell." Admitting the above explanation that the protozoon contains both somato- plasm and germ-plasm, it is easy to understand how un- equal fission might separate the one from the other, thus originating two forms of cells, mortal and immortal; but this Weismann is not likely to admit, asserting as he does that the germ-plasm becomes changed into somato- plasm. ''It is not a little remarkable," says Prof. Vines, " that Prof. Weismann should not have offered any sug- gestion as to the conception which he has formed of the mode in which the conversion of germ-plasm into so- matoplasm can take place, considering that this assump- 12 CALIFORNIA Af'ADElIY OF SCtENCES. tion i8 the key to his whole position. He has been at considerable pains to controvert the view that somato- plasm may be converted into germ-plasm; but in mak- ing the attack he has overlooked the necessity for de- fense." Prof. Vines then gives quotations from Prof. Weismann illustrative of his theory of heredity, and of his assertion that germ-plasm must be a substance of great stability in order to be able to transmit all of the complex modifications which it acquires. He then con- tinues his objections as follows: A part of the germ- plasm, Weismann claims, goes to the formation of the somatoplasm of the developing embryo, while what re- mains goes to the formation of the nucleus of the germ- cells of the embryo. But the germ-plasm of the ovum. Prof. Vines claims, cannot influence the somatoplasm of the embryo, even from Prof. Weismann's standpoint. "This function cannot be discharged," he says, " by that portion of the germ-plasm of the ovum which has become converted into the somatoplasm of the embryo, for the simple reason that it has ceased to be germ-plasm and must therefore have lost the properties characteris- tic of that substance. Neither can it be discharged by that portion of the germ-plasm of the ovum which is aggregated in the germ-cells of the embryo, for under these circumstances it is withdrawn from all direct rela- tion with the developing somatic cells. The question remains without an answer." So much for the criticism from Prof. A\'eismann's own standpoint. From Prof. Vine's position it is open to a still more vital attack. Claiming as he does that the possibility of germ-plasm being converted into somatoplasm is an unwarrantable assumption on the part of Prof. Weismann, Prof. Vines cannot but assert that the entire theory of germ-plasm which is built upon this assumption, lawnt collapse. I'urthermore, inasmuch as the embrvo is not formed EVOLUTION OF THE COLORS OP BIRDS. 13 solely from that part of the nucleus which is purported to be the chief bearer of the germ-plasm, but from the whole nucleus plus a portion of the cytoplasm of the ovum, it is evident that the somatoplasm must have some constructive powers as well as the germ-plasm; but this is the very thing denied by Prof. Wiseman, and if true, what would be the necessity of introducing the germ- plasm at all. The somatoplasm alone would be able to be the bearer of hereditary characters, and we would then have a continuity of somatoplasm instead of a con- tinuity of germ-plasm. Prof. Weismann's reply to the criticism of Prof. Vines'* is of especial interest for it contains an epitome of his theories brought up to date. From it, it is possible to comprehend which of his views he still holds and which he rejects, a task of some difficulty in depending upon the series of his collected essays. In reply to the objec- tion of Prof. Vines that an immortal cell could not have changed into a mortal cell by fission unless there already existed within it a latent principle of mortality, Prof. Weismann appeals to the division of labor, saying: " From the one cell which performed all functions comes a group of several cells which distribute themselves over the work. In my opinion, the first such differentiation produced two sets of cells, the one the mortal cells of the body proper, the other the immortal germ-cells." Surely Prof. Weismann does not consider immortality a function of amoeban cells, or, if he does, cannot hold that mortality is another function possessed by the same cells! His explanation of the distinction between im- mortality and eternity is opportune and may throw some light on the subject. By biological immortality Weis- *Prof. Weismann's Theory of Heredity; Nature, February 6, 1890, pp. 317-323. 14 CALIFORNIA ACADEMY OP SCIENCES. mann simply means that an organism has the potential power of renewing the cycle of its existence, as long as the environment conditioning its existence remains suitable. While it can be destroyed, it does not bear within it the seeds of decay. "If, then," says Prof. Weismann, "this true immortality is but cyclical, and is conditioned by the physical constitution of the pro- toplasm, why is it inconceivable that this constitution should be under certain circumstances and to a certain extent, so modified that the metabolic activity no longer follows its own orbit, but after more or fewer revolutions comes to a standstill and results in death? All living matter is variable; why should not variations in the protoplasm have occurred which, while they fulfilled cer- tain functions of the individual economy better, caused a metabolism which did not exactly repeat itself, i. e., sooner or later came to a condition of rest?" This explanation, although rather vague, does indeed seem to throw some light upon the way in which mortal- ity might have originated, but his appeal to panmixia to aid him seems wholly unwarrantable. He says: " I believe that organs no longer in use become rudiment- ary, and must finally disappear solely by 'panmixie'; not through the dii'ect action of disuse, but because natural selection no longer maintains their standard of structure. What is true of an organ is true also of its function, since the latter is but the expression of the qualities of material parts, whether we can directly per- ceive their relations or not. If, then, as we saw, the immortality of monoplastids depends on the fact that incessant metabolism of their bodies is ever returning exactly to its starting point, and produces no such modi- fications as would gradually obstruct the repetition of the cycle, why should that quality of its living matter which causes immortality — nay, how could it be re- EVOLUTION OP THE COLOKS OP BIRDS. 15 tained — when no longer necessary?" The above pas- sage is open to two objections. First, he assumes pan- mixia as proved. In discussing this subject later on it will be shown that, on the contrary, panmixia appears to be largely untenable. Secondly, panmixia means a cessation of natural selection. If we assume with Weis- mann, as there seems every reason to assume, that the original unicellular organisms, and their living repre- sentatives to-day, possess a potential immortality or possibility of indefinite existence, we certainly cannot assume that some are more immortal than others. But if potential immortality be a natural attribute of life, why should natural selection be necessary to preserve this attribute, or from what could it make its selection? If natural selection is not requisite to maintain this standard of immortality, panmixia, assuming its po- tency in other instances, could have no influence in causing mortality, being merely the negative of natural selection. Prof. Weismann then replies to Prof. Vine's criticism of his theory of embryogenesis and the continuity of germ-plasm. He asserts that Prof. Vine's criticism is due to a misconception , that he does not claim that germ- plasm is ever converted into somatoplasm. In his second essay he had indeed contrasted the somatoplasm or the entire substance of the body with the germ-plasm or entire substance of the germ-cells, not having arrived at the time at the conclusions of Strasburger and 0. Hert- wig, that hereditary transmission was effected solely by the chromatin of the nuclear loops. This view he had adopted when the fourth essay was written, and his theory was accordingly somewhat modified. He made use of Na- geli'sterm, idioplasm, in an essentially differeht manner, applying it to the chromatin not only of the ovum- nucleus, but also of every cell in the body. This idio- 16 CALIFORNIA ACADEMY OP SCIENCES. plasma he asserted to be the vital formative principle of every cell, what remained being merely nutritive. The general term somatoplasm was then of course abandoned. There are, then, according to this theory, two series throughout the body, one formative, the other reproduc- tive. The formative, which is the chromatin of the nu- cleus, passes under the general term of idioplasma. When present in the germ-cells it is called germ-plasm; in the body cells," somatic idioplasm." The nutritive sub- stance is what was previously known as somatoplasm. To it also a new term was given, " cytoplasma." Hav- ing made these distinctions, Weismann explains his idea of embryogenesis. This takes place, according to his theory, by the successive halvings of the nuclear loops or germ-plasm. "Each fresh cell-division," he says, "sorts out tendencies which were mixed in the nucleus of the mother-cell, until the complex mass of embryonic cells is formed, each with a nuclear idioplasma which stamps its specific histological character on the cell." A minute part of the idioplasm he assumes to remain un- changed when the first transformation occurs, in order to preserve the continuity of the germ-plasra. This fragment of germ-plasm migrates in an inactive condi- tion from cell to cell, until it comes to the spot where it develops into the germinal cells of the next generation. How, then, does the controversy between Prof. Vines and Prof. Weismann rest? Briefly, Prof. Vines has shown that Weismann has not accounted for the intro- duction of mortality in the order of life, although it is upon the assumption of such a differentiation of cells into mortal and immortal that his entire theory rests. Vines has not shown, however, that such a differentia- tion is imf)ossible. Weismann, on the other hand, has refuted the charge of the inconsistency of assuming that germ-plasm can be converted into somatoplasm, although EVOLUTION OP THE COLORS OP BIRDS. 17 the reverse is impossible. From the destructive, it may now be well to turn to the constructive form of criticism. There have been two theories recently advanced in opposition to Weismann's — one by J. A. Eyder an^ the other by Lloyd Morgan. Eyder has presented his theory in an article entitled " A Physiological Hypothe- sis of Heredity and Variations," in the "American Naturalist.* He considers Weismann's views to be fanciful and visionary and admits of no possible com- promise. He agrees with Morgan that the introduction of a hypothetical germ-plasm, instead of making the question of heredity more simple, in reality complicates matters. He believes with H. Milne Edwards and Hux- ley that in the division of labor of the various cells of the body, all have been specialized beyond the point where further embryonic development is possible, with the exception of the reproductive cells which remain un- specialized, and hence capable of development. Spencer confirms this view of the simplicity of the reproductive cells. He says: f" The marvellous phenomena initiated by the meeting of the sperm-cell and germ-cell, natur- ally suggest the conception of some quite special and peculiar properties possessed by these cells. It seems obvious that this mysterious power which they display, of originating a new and complex organism, dis- tinguishes them in the broadest way from portions of organic substance in general. Nevertheless, the more we study the evidence the more is this assumption shaken — the more are we led towards the conclusion that these cells have not been made by some unusual elaboration, fundamentally different from all other cells, * * * the organs for preparing sperm-cells and germ- *Vol. 24, p. 85. tPrinciples of Biology, I, pp. 219-220. 2 18 CALIFORNIA ACADEMY OF SCIENCES. cells have none of the speciulty of structures which might be looked for, did sperm-cells and germ-cells need endowing with properties essentially unlike those of all other organic agents. On the contrary, these reproduc- tive centers proceed from tissues that are characterized Ijy their low organization." Besides the accusation of producing unnecessary con- fusion by the introduction of the mystical germ-i^lasm, Ryder has a much more serious charge to prefer against Weismann. He claims that the isolation of the germ- plasma in the germ-cell is in conflict not alone with the principles of metabolism, upon which modern physiology stands, but also with the law of the conservation of en- ergy. " Modern physiology," he says, " as well as the doctrine of the conservation of energy, positively forbids us to interpose any barrier between the plasma of the parent-body and that of the germ-ceils, as is done by the promulgators of the h3'pothesis of the continuity and isolation of the germ-plasma." What, then, is Ryder's theory? Briefly this: All cells of the body have some reproductive power, us shown by the healing of a wound among the most specialized organisins, by the restora- tion of a lost limli among lower forms, or of a lost organ, as the eye, for example, by still lower, and by the power of the lowest metazoa and some plants of forming anew individual from a fragment of the parent. The lower in the scale of life we penetrate, the more generally diffused and potent do we find this regenerative power. The logical inference from this is that reproductive force is most powerful where the specialization is least. ""The reproductive cells would accordingly be the least special- ized cells of the body. Moreover, they are the only cells which are normally passive and functionless. The spe- cific molecular character of the reproductive cells, then, according to Ryder, togetlier with the molecular tenden- EVOLUTION OF THE COLORS OP BIRDS. 19 cies of all the cells of the body form the efficient force for the production of a new individual. This theory would allow, nay, even necessitate, the inheritance of acquired character. Prof. Eyder states this as follows: " Molecu- lar impressions experienced in the course of variations in the modes of manifestation of, or of disturbance of the balance of the metabolism of the parent-body, are sup- posed upon this view to be transmitted as molecular tendencies to the idle or passive plasma of the germ- cells. Variations in the molecular constitution and tendencies of the germinal matter are supposed to thus arise at different times in the same parent, and that, consequently, successive germs may be thus differently impressed." The above view does not seem to be fundamentally different from Haeckel's plastidule theory, although Ry- der classes the latter with those from which his own is a departure. The chief objection to it is its vagueness, and it is to be hoped that Prof. Ryder may elaborate it at some time. There appears to be nothing expressed in Lloyd Morgan's views contradictory to the theory above stated. Morgan lays the greatest stress upon cellular continuity. He regards "the sharp distinction between body-plasm and germ-plasm as an interesting biological myth." He expresses his views on cellular continuity as follows:* " The nucleus is the essence of the cell. And the doc- trine of cellular continuity emphasizes the fact that the nuclei of all the cells of the body are derived by a pro- cess of divisional growth from the first segmentation nucleus which results' from the union of the nuclei of the ovum and the sperm. In this sense, then, however late the germinal cells appear as such, they are in direct * Animal Life and Intelligence, p. 142. 20 CALIFORNIA ACADEMY OF .SCIENCES. continuity Avith the germinal cell from which they, in common with all the cells of the organism, derive their origin. In this sense there is a true continuity of germ- ceUs." Morgan, like Ryder, believes the reproductive cells have been set apart in the division of labor, and in this he is in accord with Weismann. The agreement is not carried out in the details, however. Morgan says:" " Cell-reproduction is, however, in the metazoa of two kinds. There is the direct reproduction of differentiated cells, by which muscle-cells, nerve-cells, or others re- produce their kind in the growth of tissues or organs; and there is the developmental reproduction, by which the germinal cells under appropriate conditions repro- duce an organism similar to the parent. The former is in the direct line of descent from the simple reproduc- tion of amoeba. The latter is something peculiarly metazoan, and is, if one may be allowed the expression, specialized in its generality." Prof. Eimerf expresses himself in similar terms with regard to the continuity of body cells. He says: " If the body of the multicellular organism is thus, even according to Weismann's ideas, of secondary importance in comparison with the germ-plasm, if the latter corres- ponds to the unicellular organism, it follows that the multicellular is just as immortal or mortal as the uni- cellular. And thus it is impossible to see why, between the germ-plasm of the multicellular on the one hand,, and that of the unicellular on the other, there should exist this profound difference, that the latter acquire characters during life and transmit them by heredity, the former not, how the former any more than the 1. c, p. ]43. t Organic Evolution; English Translation, p. 71. EVOLUTION OP THE COLORS OF BIRDS. 21 latter can nourish itself and grow without being influ- enced in its nature by its nurture." The above discussion of the views of Weismann and his opponents is merely intended as a statement "of the case in an unprejudiced light so that a provis- ional conclusion may be reached, at least on some of the points in dispute. A brief summary of the details in which the two factions agree and differ may now be given: They agree: (1.) In the immortality of protozoa. (2.) That mortal metazoa have been evolved from immortal protozoa. (3.) That the reproductive cells have been set apart by the principle of the division of labor. Weismann claims: (1.) That there are two forms of plasma, germ- plasma which has a formative and cytoplasma which has a nutritive function. (2.) That the germ-plasma has the immortality of protozoa, while the cytoplasma is mortal. (3.) That the two plasmas are mutually isolated. Hence: (4.) That whatever may affect the cytoplasma of the body-cells can have no influence on the germ-plasma of the ovary. Or, in other words, that acquired characters cannot be inherited. His opponents claim: (1.) That there is only one form of plasma which may be called either somatoplasm or idioplasm. (2.) That, inasmuch as every individual is formed by repeated cell divisions of the germ-cell, there is an immortality of somatoplasm. (3.) That the inheritance of acquired characters is not in opposition to any known biological law. 22 CALIFORNIA ACADEMY OF SCIENCES. According to Ryder's hypothesis acquired characters must be inherited, but this hypothesis not yet having been demonstrated does not afford a proof that such characters are inherited. Morgan, on the contrary, points out the difficulty of framing an intelligible theory which will satisfactorily explain such inheritance, al- though at the same time claiming that there is no theo- retical evidence against it. This being the state of opinion in regard to the theories, it will be well to look to the so-called proofs of the inheritance of acquired characters; but before so doing one other theory of Weismann's bearing upon the subject must be examined, viz; panmixia, or " pammixis," according to the cor- rected version. Panmixia, according to Weismann, means the " sus- pension of the preserving influence of natural selec- tion," over an organ, part or function no longer necessary for the welfare of the species. So far all very well. We cannot quarrel with Weismann for giving a name to this cessation, but we can disagree with him as to the result whieli will be brought about; and this Ijloyd ]\rorgan luis done so ably tiiat I cannot do better than refer the reader to the passage.* ^\^eismann claims that by this failure on the part of natural selection to maintain the standard of excellence of an organ, it will degenerate and ultimately disai)pear. Lloyd Morgan shows thai pammixis can only produce a reduction from the survival mean to the birth mean. Selection, by eliminating such individuals as possess inferior parts, makes the standard of excellence of the survival mean considerably above the standard of birth mean. If then, selection cease to operate, the birth mean stand- ard will 1)0 again restored. Or, to express it in figures, 'Animal Life and Intelligence, p. IS!). EVOLUTION OF THE COLORS OF BIRDS. 23 if the birth mean standard of an organ equal 3, and the survival mean 5 when selection is operative, the standard cannot possibly fall below 3 when selectioji ceases. Mr. J. T. Cunningham criticises pammixis as follows:* " The fallacy of this argument is so obvious that it is surprising it should be for a moment accepted. For what is stated of the maxima variations is equally true of the minima. In the absence of all selection the minima variations will be combined in sexual union with variations superior to themselves, and therefore in each successive generation the minimum will be raised. Thus the only possible result of pammixis, on Weis- maun's theory of variation, will be the production of uniformity in a disused or useless organ, and the de- generation or disappearance of such an organ will be absolutely impossible." In an article on "The Factors of Organic Evolution,"! Prof. Geo. J. Romanes calls attention to the fact that he had enunciated the principle of pammixis under the name "Cessation of Selection," as early as 1873. He had not claimed, however, that this cessation of selec- tion could of itself produce the total disappearance of an organ or part. As an instance of this, he supposes a structure to have been raised from to an average of 100, and then to have become wholly useless, so that natural selection would be no longer operative in main- taining the standard. Reversal of selection would then set in, due to economy of growth, and variations 101, 102, 103, etc., would be eliminated, while variations 99, 98, 97, etc.", would be favored. To continue the explana- tion in the writer's own words: "For the sake of definition, we shall neglect the influence of economy * The New Darwinism, Westminster Review, July, 1891, p. 23. + Nature, XXXVI, Aug. 25, 1887, pp. 401-407. --J C:ALIF0RNIA academy of HCIE^'CES. acting; bflow 100, and so isolate the effects due to the mere withdrawal of selection. By tlie conditions of our assumption, all variations above 100 are eliminated, ^\■hile below 100 indiscriminate variation is permitted. Thus, the selective premium upon variation 99 being no greater than upon OS, 98 would have as good a chance of leaving offspring which would inherit and transmit this variation as would 99; similarly, 97 would have as good a chance as 9.S, and so on." He then shows how there would be a constant tendency toward reduction in the part, but that the greater the reduction the less pos- sibility of future reduction would remain. "Thus," he says, "theoretically the average would continue to diminish at a slower and slower rate, until it comes to 50, where the chances in favor of increase and diminu- tion being equal, it would remain stationary." Prof. Romanes then gives examples of parts which he thinks have degenerated through cessation of selection. He considers the cases where the phylogenic stages are omitted in the developing embryo to be instances in point, and argues that such omissions cannot be ex- plained by economy of growth, for in allied forms where economy would l)e equally operative the structure per- sists. Neither can the absence of such parts be due to disuse, Prof. Pomanos contends, for they were not gen- erally produced by use. The case of hard coverings, which are de\elope(l l.iy natural selection as a protection to certain animals, and after^vards lost \vhen their period of usefulness is past, is also cited as an example of de- generation without disuse Pammixis, then, is not new as a theor}', nor is it (he only available explanation of degeneration. Ro- manes himself suggested three alternatives. Besides reversal of selei-tion, he has stated two other factors, as at earlier EVOLUTION OF THE COLORS OF BIRDS. z5 periods of life, wliich progressively pushes back the de- velopment of a rudiment to a more and more remote embryonic stage of growth; and the second is the event- ual failure of the principle of inheritance itself. For, ' whether or not we believe in Pangenesis, we cannot but deem it in the highest degree improbable that the influ- ence of heredity is of unlimited duration.' " The former of these two factors is the same as Prof. Cope's principle of retardation, while the latter has also been independ- ently stated by Cope, as will be seen in a subsequent quotation. There are, then, five theories besides pam- mixis by which degeneration of parts may be explained, viz: (1) reversal of selection, (2) economy of energy, (3) disuse, (4) retardation, and (5) the failure of heredity. In some cases the loss of an organ or member is an ad- vantage, and then natural selection Taa,y aid in elimina- ting it. An instance of this is to be found in insects inhabiting islands, which would be blown to sea and perish if they possessed the power of flight, and in which the wings are aborted or entirely absent. There are many cases, however, in which there is no such direct advantage to be discovered in the reduction of a part. To some of these cases the principle of economy enun- ciated by Darwin might well apply. This principle assumes that the organism has a given amount of force to expend, and that if one part be useless the growth force which has been expended in maintaining it will be diverted to some other channel. Thus birds, like the ostrich, in which the wings are aborted, have legs pro- portionately powerful. The third principle is disuse. It is universally admitted that whenever a part is not used during the lifetime of an individual it degenerates to a certain extent. The principle of disuse merely assumes that such acquired degeneration can be inher- ited. Cope enunciated the fourth and fifth principles, 26 CALIFORNIA ACADEMY OF SCIENCES. independently of Romanes.* When any part or the whole of an individual is retarded in its growth, so that the animal begins to breed before reaching maturity, Cope holds that the descendents will be deficient in such parts as were not fully developed in the parent. The statement of the action of this law in producing degene- ration of parts is as follows: " 'Retardation' continued terminates in extinction. Examples of this result are common; among the best known are those of the atrophj^ of the organs of sight in animals inhabiting caves. * '"' I would suggest that the process of reduction illustrates the law of ' retardation ' accompanied by another phe- nomenon. Where characters which appear latest in em- bryonic history are lost, we have simple retardation — that is, the animal in successive generations fails to grow up to the highest point of completion, falling farther and farther back, thus presenting an increasingly slower growth in the special direction in question. Where, as in the j^resence of eyes, we have a character early assumed in embryonic life, retardation] presents a somewhat different ^^hase. Each successive generation, it is true, fails to come up to the completeness of its pre- decessor at maturity, and thus exhibits 'retardation;' but this process of reduction of rate of growth is followed by its termination in the part long before growth has ceased in other organs. This is an exaggeration of retardation, and means the early termination of the process of force-conversion, which has been previously diminishing steadily in activity." The subject of use and disuse need not be considered in further detail. From the above it is evident that there are many explanations of the phenomena of degenera- tion and that pammixis cannot be at best more than one of several factors. • Origin of the Fittest, p. 13. EVOLUTION OP THE COLORS OF BIRDS. 27 Having disposed of the theoretical aspect of the ques- tion of use and disuse and the inheritance of acquired characters, a few words on the practical side of the case may now be in order. In the first place it will be advis- able to enquire what an acceptance of the views of Weismann involves. Some of the consequences are well shown by Mr. J. T. Cunningham, in his intxoduction to the English translation of Elmer's Organic Evolution. He calls attention to the abnormally lengthened tongue of the woodpecker, which can be greatly protruded and thrust into holes to extract insects. The lengthened tongue, the Neo-Darwinians claim, has been produced solely by the selection of those individuals in which it was longest. They cannot but admit with the Lamarck- ians, however, that constant exercise of the tongue in the individual, especially the constant stretching to which it would be subjected in the effort to reach far- ther, would increase its length; but in admitting this they have involved themselves in the paradox of assum- ing that the tongue has become lengthened during the course of ages, and that it has also been lengthened in the individual by the Lamarckian factor of use and dis- use, but that the lengthening which has occurred in the race is in no wise related to the lengthening that has taken place in the individual. " Which is very like the argument," says Cunningham, "that the Iliad and the Odyssey were not written by Homer, but by another man of the same name who lived at the same time." Another difficulty in the way of the Neo-Darwinian argument to which Cunningham, among others, has called attention, is its inability to account for the origin of totally new characters. Even though it may be able to account for the lengthened neck of the giraffe by selection, it is impossible, Cunningham argues, to ex- plain the origin of horns by this principle. From what "2'S CALIFOKNIA ACADKMY OF SCIENCES. is the selection to be made? " No other mammals," he says, have ever been stated to possess two little symmet- rical excrescences on their frontal bones as an occasional variation; what then caused such excrescences to appear in the ancestors of horned ruminants? Butting with tlie forehead would jiroducc them, and no other cause can be suggested which would." An inconsistency which has been pointed out by liomancs, Osborn and Le Conte, is the fact that the Neo- Darwinians admit the Lamarckian factors among proto- zoa. Romanes has pointed this out with especial clear- ness in his article entitled " Weismann's Theory of Heredity "* He calls attention to the fact that inas- much as natural selection is unavailing without varia- tion, and that ^'ariation, according to Weismann's view is due to the sexual admixture of different traits, there can be no individual variation among unicellular and parthenogenetic organisms, and hence natural selec- tion cannot be a factor in producing new forms. Weis- mann, indeed, sees this to be the case and admits that modifications in such animals must be due solely to the direct action of tlic environment. Two objections have here been interposed. Prof. Osborn asks why, if the direct action of the environment was once a factor of evolution, as Weismann admits, it should ever have ceased to be such if its period of usefulness did not ter- minate. f Xow it is apparent that the period of useful- ness of the Lanuirckian factors does not terminate with the protozoa, and C(jnsequently natural selection itself would have tended to i)reserve them. Prof. Romanes' suggestion was not stated in the form of an objection, alth(jugli such is clearly implied. It is in l>rief as fol- (.'niiteuiponivv Review, May, l.StIO, \fp. 086-(ill!). tAinerii-nu Naturalist, xxiii, p. EVOLUTION OF THE COLORS OF BIRDS. 29 lows: The germ-plasm of Prof. Weismann is a highly stable substance unaffected from within or without. Variations occur by sexual admixture, but as there is an immortal chain of germ-plasm all variations may be ultimately referred back to the unicellular organism, and hence all variations must have been due originally to the direct actions of the environment in producing changes in the protozoa. In considering the observed cases of transmission of acquired characters, the subject of the supposed trans- mission of mutilations may be first discussed. As is well known, many cases of such transmission are on record, but Weismann has shown that a large number of these are untrustworthy. Undue significance however, lias been attached to the validity of such cases. In his in- troduction to the English translation of Elmer's Organic Evolution, Mr. J. T. Cunningham has made a sugges- tion, the importance of which has been generally over- looked. He says: "The fact that artificial malforma- tions are not usually inherited is no argument against the inheritance of acquired characters. In all animals, from the lowest up to reptiles, recrescence of lost parts takes place, and the reappearance of lost parts in the next generation in mammals and birds seems to me to be simply r|ecrescence slightly postponed." Lloyd Morgan, speaking of the evidence of the inherit- ance of acquired characters, says:* "Attempts have been made to furnish such evidence by showing that certain mutilations have been inherited. I question whether many of these cases will withstand rigid criticism. Nor do I think that mutilations are likely to afford the right sort of evidence one way or the other. We must look to less abnormal influences. What we require is evidence * Animal Life and Intelligence, p. 163, 30 CALIFORNIA ACADEMY OF SCIENCES. ill favor of or against the supposition that moilificationx of the body-cells are transmitted to the germ-cells. Now these modifications must clearly be of such a nature as to be receivable by the cells without in any Avay de- stroying their integrity. The destruction or removal of cells is something very different from this. If it were proved that mutilations are inherited, this would not necessarily show that normal cell-modifications are trans- missible. And if the evidence in favor of inherited mutilations breaks down, as I believe it does, this does not show that more normal modifications such as those with which we are familiar, as occurring in the course of individual life, are not capable of transmission." "Weismann has devoted some attention to the reported cases of the inheritence of mutilations, and has reached the conclusion that all the published instances are either untrustworthy or of such a character that they do not conclusively prove that a case of mutilation has ever been inherited. In commenting upon his explanation of reputed cases of the transmission of rudimentary tails, he says;* " We have seen that the rudimentary tails of cats and dogs, as far as they can be submitted to scientific investiga- tion, do not depend upon the transmission of artificial mutilation, but upon the spontaneous appearance of de- generation in the vertebral column of the tail. The opinion may, however, be still held that the customary artificial mutilation of the tail, in many races of dogs and cats, luis at least produced a number of rudimentary tails, although, perhaps, not all of them. It might be maintained that the fact of the spontaneous appearance of rudimentary tails does not disprove the supposition that the character may also depend upon the transmis- sion of artificial mutilation. Essays on Hc-ve lit y, 18(»1, I, p. 443. EVOLUTION OP THE COLORS OF BIRDS. 31 "Obviously, such a question can only be decided by experiments; not, of course, experiments upon dogs and cats, as Bonnet rightly remarks, but experiments upon animals the tails of which are not already in a process of reduction. Bonnet proposes that the question should be investigated in white rats or mice, in which the length of the tail is very uniform, and the occurence of rudimentary tails is unknown." Weismann accordingly performed these experiments, and there can be no doubt that they have been done in a thorough and scientific manner. The result has been purely negative, mice of the fifth generation bearing young with the tails of normal length. Weismann, in- deed, admits that these experiments do not constitute a complete disproof of a possibility of transmitting mutila- tions, but justly claims that, in comparison with the cases of such supposed transmission occurring com- pletely in a single generation, and where but one parent was affected, the possibilities of transmissions were in- finitely greater in his experiment. If, however, the suggestion of Cunningham, that the non-inheritance of mutilation in higher animals is comparable with regen- eration of lost parts among lower forms, but delayed to the following generation, we can easily understand that while mutilations might be inherited, the contrary would be the rule, and such inheritance would be due to an abnormal condition of the organism. Cunning- ham, furthermore, not unjustly, insinuates that even the cautious Prof. Weismann may have been betrayed into asserting a little more than he knew in order to prove his point. For example, he says:* " Prof. Weis- mann mentions the feet of Chinese ladies, which he says are still, when uncompressed, as large as if the * Organic Evolution, Translator's Preface, p. x. '.->2 CALIFORNIA ACADEMY OF SCIENCES. practice of artificially compressing them had not been practiced for centuries. But he does not tell us whether he ever saw a Chinese young lady, or if he has made any observations on the feet of Chinese young women." Eimer has mentioned a number of cases of supposed mutilation which I have not seen refuted. In arguing for the inheritance of mutilations, he says:* "That injuries, when continued for an extremely long time, may be inherited is proved, to my mind, by atrophied (rudimentary) organs. The degeneration of these organs depends incontestably on disuse; in consequence of dis- use the blood-supply is diminished, in consequence of the decrease of nutrition degeneration takes place. If we consider the course of gradual degeneration, e. g. of the tail as it must have taken place in the higher mam- mals, to have proceeded in this purely physiological manner from the tip toward the root, the process is much the same as if the tip of the tail had been in many successive generations amputated, and the short- ening had been inherited and then the shorter tail thus acquired had been farther shortened artificially, and so on. In any case, in the degeneration of the tail an acquired character has been inherited by the offspring, a character which, in the causes of its origin, is closely similar to a perpetually rejieated mutilation. Great periods of time, however, have been necessary in this case for the accomplishment of a final result." This example of Prof. Elmer's seems, however, to be an assumption of the validity of the point in dispute. His opponents could, of course, claim that the reduction in the length of the tail was due solely to the selection of the shortest. His examples of observed cases of in- heritance of mutilations, however, do not appear to be ~ Organic Evolution, Eng. translation, p. 170. EVOLUTION OF THE COLORS OF BIKDS. 33 susceptible of the criticism of a misinterpretation of the facts. Two only need here be given.* "A. Decandolle describes one such case with the assurance that it is per- fectly true. In the year 1797 a girl twenty-one years old was thrown from a carriage, andii) consequence had a scar about five centimeters wide over the left ear and temple which remained without hair. Married in 1799, she bore a son in 1800, in whom the hair was absent from the same area and remained so. The son of the man, born in 1836, had no such defect, but it was pres- ent in his grandson born in 1866, and in 1884 in this last individual when he was eighteen years old the pecu- liarity was disappearing. "Dr. Meissen of Falkenberg, records in the number of Humboldt for June, 1887, the following case of in- heritance of an injury in his own family: ' When I was seven or eight years old I had the chicken-pox, and I recollect with complete distinctness that I scratched one of the pustules on the right temple in consequence of which I had a small white scar at this spot. Exactly the same scar, which I had of course ceased to think of, on exactly the same spot, was present on my little son, now fifteen months old, when he came into the world. The resemblance is so perfect that it surprises everyone who sees the little mark.' " It is unnecessary to multiply examples of reported cases of the inheritance of mutilations. A single trust- worthy instance is sufficient to offset an indefinite amount of evidence to the contrary; more especially when the Neo - Lamarckians themselves assert that •such inheritance, if it occurs at all, is abnormal. The explanation given by Weismann of the inheritance of epilepsy in guinea pigs as described in the experi- '1. c, p. 177. 3 34 CALIFORNIA ACADEMY OF SCIENCES. nients of Brown-Sequard and Obersteiner appears forced and inexcusably far-fetched, but it will be unnecessary to dwell longer upon such cases. SufKce it to say, that epilepsy superiiaduced by severing certain peripheral nerves has been transmitted to the following generation, but that Weismann evades the experiment, first by sug- gesting that it was merely the predisposition to the dis- ease — due to a general derangement of the nervous sys- tem that was inherited, and secondly suggesting that the disease was transmitted by microbes penetrating the reproductive cells. An almost endless number of instances have been re- ported of the transmission of acquired characters, while the Neo-Darwinians have replied to many of them, ex- plaining the facts after their own fashion. It will be obviously impossible to give all of the cases which have been brought to light, but a few representative ones may be detailed. The evidence divides itself into two classes, viz: observed instances of transformation which appear to be due to the direct action of the environment; and, second, structures, functions, or traits which could only have resulted from the inheritance of acquired charac- ters . In the first category may be mentioned the case of the Japanese goldfish of Dr. Wahl, which Prof. Ryder records,* which, by close confinement and abundant food, were greatly modified, " enormous and abnormally lengthened j)ectoral, ventral, dorsal, double and caudal fins " being developed. " Some of the races of these fishes have obviously been affected in appearance by abundant feeding," he states, " as is attested by their short, almost globular bodies, protuberent abdomens and greedy hab- its," etc. Lloyd Morgan gives some interesting instances ■*Am. Ni)t., vol. -ii, page 89. EVOLUTION OP THE COLORS OF BIRDS. 35 of observed cases of the direct action of the environment in affecting a race. One of the finest is the transforma- tion of the brine-shrimp, Artemia, reported by Schman- kewitsch: "One species of this crustacean, Artemid sa- lina," says Lloyd Morgan, "lives in brackish water, while A. inilhausenii inhabits water which is much Salter. They have always been regarded as distinct species, dif- fering in the form of the tail lobes and the character of the spines they bear. And yet, by gradually altering the saltness of the water, either of them was transformed into the other in the course of a few generations. So long as the altered conditions remained the same the change of form was maintained." AVhat is to be said of such cases? Do they constitute a proof positive of the inheritance of acquired characters? At first sight they certainly do appear to be conclusive and final, but a candid examination of them compels us to admit of the possibility of a different interpretation. The two examples mentioned are fairly representative of a large number of similar instances. The whole diffi- culty with them lies in the fact that when the organism is restored to its former conditions the change does not persist. Does the son of a blacksmith inherit the strong arms of his father? Probably he does, but this is not equivalent to asserting that he inherits the strength acquired by his father in following his vocation. It is not improbable that his father became a blacksmith be- cause he was naturally strong or was predisposed to develop unusual strength. We must first in every case assure ourselves that the predisposition does not exist in the animal and only requires a favorable environment to be developed. Secondly, it must be demonstrated that there is a progressive change from one generation to the next. This there apparently was in the case of the goldfish, for a period of six years was required for 36 CALIFORNIA ACADEMY OF Sl'IENCES. the production of some of the forms. But even in cases where the change lasts only as long as the altered envi- ronment is operative, although the permanent transmis- sion of acquired characters is not demonstrated, it is rendered highly probable. Cunningham gives an excel- lent analogy illustrative of this. He says:* " If a plant with a vertical stem is placed in a horizontal position, the light coming from above, the end of the stem will bend up toward the light, partly by growth, partly by flexure. Such a plant was so placed, and, after a certain time, when the upward flexure was established, it was turned round so that the tip pointed downwards. Of course the flexure was gradually reversed until the tip pointed upwards again. After the same interval the [)lant was reversed once more. This was continued for some days, the plant being reversed at regular intervals. At last, when the time came for turning the plant round, the operation was not performed, it was left undisturbed. But then the plant began to reverse its flexure of its own accord, and actually turned its tip downwards, away from the light. By the regularly repeated reversal of position a rhythm had been set up in the life of the plant, and even when the cause which excited this rhythm ceased, the rhythm continued." Weismann himself gives some instances of these " after-eft'ects " in plants, such as the case of the sun- flower, which is as ftdlows:! " if vigorous plants of the sunflower, grown in the open air, be cut off close to the ground and transferred to complete darkness, the exam- ination of a tube flxed to the cut surface of the stem will show that the escape of sap does not take place uni- formly, but undergoes periodical fluctuation, being strongest inythe afternoon and weakest in the early * The New Dfirwiuism, Westmiuster Review, July, ISSl, p. 41C. t Ebsays upon Heredity, 189], I. p. 410. EVOLUTION OF THK COLORS OF BIPEDS. 37 morning. Now the cause of this daily periodicity in the flow of sap depends upon the periodical changes due to the light to which the plant was exposed when it was growing under normal conditions. When plants which have been grown in darkness from the first are similarly treated, the flow of sap does not exliibit any such peri- odicity." In commenting on these instances, Weis- mann says: "All this is certainly very interesting, and it proves that periodical stimuli produce periodical pro- cesses in the plant, which are not immediately arrested when the stimulus is withdrawn, and only become uniform gradually and after the lapse of a considerable time. But I certainly claim the right to ask what connection there is between these facts and the transmission of acquired characters? All these peculiarities produced by exter- nal influences remain restricted to the individual in which they arose; most of them disappear comparatively soon, and long before the death of the individual." From the theoretical standpoint of Prof. Weismann this is doubtless correct. But it has been shown, I think, that Prof. Weismann's theory of the continuity of germ- plasm is not onl}'' unproven but highly improbable. Moreover, it has been shown that the continuity of the body plasm is highly probable. But if this be true, then there is, to say the least, a strong analogy between a rhythm which can be established in the somatoplasm and repeated during the life of the individual and a rhythm which can be established in the history of a race. Cunningham has well pointed out, however, that the Neo-Lamarckians do not claim that a change due to the environment can be established in a single generation. All that is claimed is, that when a particular environ- mental influence is continued from generation to gen- eration, the offspring successively inherit a progressive o8 CAHI^'OKNIA ACADEMY OF SCIENCES. predisposition to be modified, until, in the course of time, the modification takes place, when the cause is no longer operative, as in tho case of the after effects just considered. Mr. D. G. Elliot, in a recent address on the inheritance of acquired characters delivered before the American Ornithologists' Union,* relates au instance of the ob- served inheritance of an acquired habit in birds as fol- lows: " Currituck Sound, in North Carolina, where wild fowl are accustomed to pass the greater portion of the winter, is a great resort of sportsmen, who pursue the birds in every way to accomplish their destruction. This, at length, was carried to such a degree that the fowl had no place left for them to rest during the day. Some years ago the gunners were surprised to find that whenever the weather permitted, as soon as a gun was fired in the early morning the birds would rise and be- take themselves to the ocean, and remain congregated on the water just beyond the line of the breakers, and would not return until night closed in. This custom was acquired by birds of succeeding years, until the habit has become apparently established. Now it may be said that this is not au acquived habit, but the result of example, the old birds leading: the young to the sea. But this would be to assume that the majority of the birds which commenced this habit had survived to re- turn to this locality every winter. And even if the young, without at first comprehending the reason for so strange a proceeding, merely followed the old birds, is it reasonable to suppose they would remain in such an unusual locality throughout the day, deprived of their food, which could be obtained in profusion on the other side of the narrow beach? It must have been something 'Auk, ix, Jan. 1S!)L', ijp. 77-104. EVOLUTION OP THE COLORS OF BIKDH. 39 more powerful than the mere example of the flight of the old birds to the ocean, witnessed by the young for the first time, which compelled them to remain. Can we not more reasonably presume that it was the knowl- edge acquired by the parents that this was a secure method to escape from a threatened danger, and trans- mitted to the young, who assumed the habit as a part of their nature?" Mr. Elliot then mentions numerous cases of the change of nesting habits in birds. He alludes to the instance reported by Coues in Birds of the Northwest, of the geese of the Yellowstone, which build in trees in- stead of on the ground, which is the usual habit of these birds. He furthermore calls attention to the case noted by Audubon of the change in nesting habits of the her- ring gulls on White Head Island, in the Bay of Fundy, which during the lifetime of a single man had deserted the ground in favor of trees owing to the perse- cution to which they had been subjected. "A remark- able effect of this transmission of an acquired charac- ter," says Mr. Elliot, " is that the young hatched in the trees do not leave the nest until they are able to fly, while those hatched in nests on the ground run about in less than a week and conceal themselves at the sigjjt of man among the moss and plants." But cannot these instances of Mr. Elliot's be otherwise interpreted? I think they can. It is impossible to prove the inheritance of acquired habits by citing ex- amples which could best be thus explained, but which might be otherwise accounted for. In the first instance mentioned, the majority of the birds which commenced the habit might have survived. Or, a smaller number might have been sufficient if we admit that birds have sufficient language to give warning of danger. More- over, Mr. Elliot's argument that the inducement of ob- 40 CALIFORNIA ACADEMY OF SCIENCES. taining food would be so strong as to compel the young birds to ignore the example of their elders really reflects upon his own assumption, for it seems difficult to con- ceive that a new adjustment of such force as this instinct is supposed to be, could be inhe^rited in the course of a few generations. The argument derived from the change in nesting habits appears to have still less force. Mr. Elliot assumes that nest building is an instinct, l>ut this assumption is unproven and has been emphatically doubted by Wallace. In his Philosophy of Birds' Nests,* he says: " At all events, till the crucial experiment is made, and a pair of wild birds, raised from the egg with- out ever seeing a nest, are shown to be capable of mak- ing one exactly of the parental type, I do not think we are justified in calling in the aid of an unknown and mysterious faculty to do that which is so strictly analog- ous to the house-building of savage men." Darwin has given many instances of the inheritance of acquired habits which, however, have been skillfully combated by William Piatt Ball.f He cites, for ex- ample, the inheritance by a colt of the paces of her mothei', but suggests that " selection of the constitu- tional tendency to tliese paces, and imitation of the mother by the colt, may have been the real causes." He calls attention to the fact that the songs of birds are not inherited, but arc learned from their parents, and says: " If use-inlieritance has not fixed the song of birds, why should we suppose that in a single generation it has transmitted a newly-taught method of walking or trot- ting." He speaks of the supposed inheritance by dogs of the intelligence acquired by contact with man, which he explains thus: " But selection and imitation are so 'Natural Seleetiuii, pp. 108-109. t Are the Effects n{ Use and Disuse Inherited? Humboldt Library, pp 3I-:W. EVOLUTION OF THE COLORS OF BIRDS. 41 potent, that the additional hypotliesis of use-inheritance seems perfectly superfluous. Where intelligence is not highly valued and carefully promoted by selection, the intelligence derivable from association with man does not appear to be inherited. Lap-dogs, for instance, are often remarkably stupid." It seems to me that Ball does not establish his point in this instance. To be sure, it might be claimed that thoroughbred dogs had attained their intelligence through selection alone (although this I should be inclined to question), but such dogs are generally, if not universally, bred with one especial end in view, either speed, hunting qual- ities, fighting qualities, beauty or eccentricty; but how often are they bred for intelligence? Moreover the most intelligent dogs are not infrequentlj' curs. A large number of the most remarkable stories of canine sagac- ity are told of animals without a pedigree. But these dogs have not been selected at all, for the most part. What is the fate of a large litter of puppies of a cur? A part of them are generally destroyed in early infancy, aiid this in a manner practically impartial so far as in- telligence is concerned. The rest are generally given away, but what evidence have we that the less intelli- gent of them are killed by their new masters, while the more intelligent survive to perpetuate the race? Romanes has called attention* to the inheritance of an instinct in dogs which he considers especially invul- nerable in support of the inheritance of acquired habit. For an instinct to have been established solely by nat- ural selection, it must be of sufficient importance to be essential to the life of the race, so that those individ- uals possessing it may alone survive. This is not the " The Factors of Organic Evolution. Nature. AufjuHt -J.), 1887-XXXVI, p. 406. 42 CALIFORNIA A(^\DEMY 01<' SCIENCES. case with the instinct which dogs possess of turning tiround several times before lying down, in order to trample down a bed, a relic of primitive comfort which surely could not have become established by the survival of the fittest. "Or,"' says Romanes, "if this instance be held doubtful, what shall we say to the courting in- stincts in general, and to the play-instincls of the bower- bird in particular, which are surely quite without mean- ing from any utilitarian point of view? And these in- stincts naturally lead to the ;esthetic faculties of mankind, few of which can be j^ossibly ascribed to natural selec- tion, as Mr. Spencer very conclusively shows." Weismann and Ball have both combated this, as, in- deed, they are bound to do to be consistent with their theory. Thus Ball says: " The emotional susceptibility to music and the delicate perceptions needed for the higher branches of art, were apparently the work of natural and sexual selections in the long past. Civiliza- tion, \\'ith its leisure and wealth and accumulated knowl- edge, perfects human faculties by artificial cultivation, develops and combines means of enjoyment and dis- covers unsuspected sources of interest and pleasure, -vr * -,'r gyj- i^Qodern lesthetic advance seems to be almost entirely due to the culture of latent abilities, the formation of complex associations, the selection and encouragement of talent, and the wide diffusion and imitation of the accumulated products of the well-culti- vated genius of favorably varying individuals. The fact that uneducated persons do not enjoy the higher tastes, and the rapidity with which such tastes are ac- ijuired or professed ought to be sufficient proof that modern culture is brought about by far swifter and more potent influences than use-inheritance." What has Mr. Ball shown in the above paragraph? If he has proved anything it certainly is that natural selection has not EVOLUTION OP THK COLOKH OF I'.IRJJS. 4o originated, even if it has been instrumental in the de- velopment of the aesthetic faculties. In speaking of the culture of latent abilities he has yielded a most import- ant point. There Avas obviously a time in the evolution of organic life when piano playing, or, in more general terms, appreciation of harmony, was not even a latent faculty. It would be taxing our credulity to assume, for example, that amoeba possessed it. Then it must, at some time, have come into existence as a latent faculty, and later on been developed by use, or culture, as Ball calls it; and this developed faculty has been inherited. Spencer published in the yineteenth Ceidurij for April and May, 1886, two essays, which have since appeared in a separate form, entitled "The Factors of Organic Evolution." " Among the most important criticisms of this work is the one by Romanes in an article bearing the same title, which appeared in Nature August 25, 1887; and Ball's criticism in his pamphlet, "Are the Effects of Use and Disuse Inherited?" Spencer gives three forms of evidence in proof of the inheritance of acquired characters — (1) the crowding of teeth in dogs and reduced size of the jaw in civilized man; (2) the correlation of different parts of the organism, and (3) the apparent direct influence of the environment in altering the surface of an organism. Romanes and Ball agree that Spencer has failed to prove his first point. Romanes says, in regard to this: " Be it observed, I am not disputing that disuse may in both these cases have co-operated with the cessation of selection in bringing about the observed result. In- deed, I am rather disposed to allow that the large amount of reduction described in the case of the dogs as having taken place in so comparatively short a time, is strongly suggestive of disuse having co-operated with the cessa- tion of selection. But at present I am merely pointing 44 CALIFORNIA ACADEMY OF SCIENCES. out that Mr. Spencer's investigations have here failed to exhibit the crucial proof of disuse as a reducing cause, which he assigns to them; it is not true that in this case ■disuse ' remains as the only conceivable cause.' "* The third argument, as Romanes asserts, is too theo- retical to be considered as a proof, but the second, in regard to the correlation of parts of the organism is of great importance, and, according to the opinion of Romanes, " virtually proves the truth of the Lamarckian assumption." So important is this particular case that it is worthy of a somewhat extended consideration. Sjieneer takes the giraffe as illustrative of his point. He calls atten- tion to a statement of Darwin's that " the prolonged Tise of all the parts together with inheritance will have aided in an important manner in their co-ordination." " A remark," observes Spencer, " probably having reference chietiy to the increased massiveness of the lower part of the neck; the increased size and strength of the thorax required to bear the additional burden, and the increased strength of the fore legs required to carry the greater weight of both. But now I think that further consideration suggests the belief that the en- tailed modifications are much more numerous and re- mote than at first appears; and that the greater part of these are such as cannot be ascribed in any degree to the selection of favorable variations but must be ascribed exclusively to the inherited effects of changed func- tions." Mr. Spencer then describes the mechanism of locomotion in the giraffe, the short hind limbs whicli must keeji paci^ with the long fore limbs, and the con- sequent complex series of changes of bones, muscles and nerves which nrust have taken place in order to bring 1. e. p. 40.T. K VOLUTION OF THE COLORS OF BIRDS. 45 about this result. This might very easily be explained, indeed, by the effects of inherited use and disuse. " If the effects of use and disuse of parts are inheritable," says Mr. Spencer, "then any change in the fore parts of the giraffe which affects the action of the hind limbs and back will simultaneously cause, by the greater or less exercise of it, a remoulding of each component in the hind limbs and back in a way adapted to the new demands; and generation after generation the entire structure of the hind quarters will be progressively fitted to the changed structure of the fore quarters, all the ap- pliances for nutrition and innervation being at the same time progressively fitted to both." But the factors of use and disuse aside, we must assume that all of these complex changes occurred simultaneously. It might be contended that slight variations in one direction which were advantageous might take place in one generation, and the correlative changes in other parts at some future time. In reply to this Mr. Spencer says: " Besides the fact that until this secondary variation occurred the primary variation would be a disadvantage, often fatal, and besides the fact that before such an appropriate secondary variation inight be expected in the course of generations to occur, the primary variations would have died out; there is the fact that the appropriate variation of one bone or muscle in the hind quarters would be useless without appropriate variations in all the rest — some in this way and some in that — a number of appro- priate variations which it is impossible to suppose." Mr. Ball either cannot or will i:iot see the force of Spencer's objections. He says: "All that is needed is that natural selection should preserve the tallest giraffe through times of famine by their being able to reach otherwise inaccessible stores of foliage. The continual variability of all parts of the higher animals gives scope 46 CALIFORNIA ACADEMY OF SCIENCES. for innumerable chaiages and nature is not in a hurry. Mr. Spencer, however, saj^s that the chances against any adequate readjustments fortuitously arising must be in- finity to one. But he has also shown that altered de- gree of use does not cause the needed concomitant variation of co-operative parts. So the chances against a beneficial change in an animal must be, at a liberal estimate, infinity to two. Mr. Spencer, if he has proved anything, has proved that it is practically impossible that the giraffe can have acquired a long neck, or the elk its huge horns, or that any species has ever acquired any important modification." Mr. Ball then draws attention to the facts which Wal- lace has adduced in his recent work, "Darwinism," proving that constant and independent variation is the rule among all animals and plants. He then says: " The lengthened wing might be gained in one genera- tion, and the strengthened muscle at a subsequent pe- riod ; the bird in the meanwhile drawing upon its surplus energy, aided (as I would suggest) by the strengthening effect of increased use in the individual." This expla- nation is open to two objections: First, the one already raised by Mr. Spencer, that before the second correlative variation appeared the first would be lost; and, second, the suggestion of Cunningham in regard to assuming that use could develop the character required, but that the individual thus favored could not transmit the vari- ation, but that posterity must wait for the same vari- ation to arise spontaneously. This hypothesis is so forced, illogical and absurd, that so long as a better one can be found it should be adopted. But one more class of evidence need be discussed, that furnished by paleontology. Prof. Henry F. Osborn has called special attention to this subject on two different EVOLUTION OF THK COLORS OF BIRDS. 4/ occasions." He saj^s: " The evidence is of a direct and indirect character. The direct evidence is that hj actual observation in complete paleontological series, the origin of adaptive structures is found to conform strictly to the lines of use and disuse. The indirect proof is that the natural selection of chance variations is unsupported by observation and is inadequate to explain the various phenomena of the second class." Special attention is drawn to the evolution of teeth, in which every grada- tion may be traced from the simple conical reptilian tooth to the highly complex molars of some mammals. Osborn has enunciated the two following laws of cusp growth: " (1) The primary cusps first appear as cuspules, or minute cones, at the first points of contact between the upper and lower molars in the vertical motions of the jaw. (2) The modeling of cusps into new forms, and the acquisition of secondary position, is a concomitant of interference in the horizontal motions of the jaws." Fronr the above laws it is evident that the variations in the race are the same as the variations in the indi- viduals, caused by the use and disuse of parts, and a causal connection between the two is inferred. This proof of the inheritance of the characters of use and dis- use has been criticised by Poulton. In a foot-note to Weismann's Essays upon Heredity,! he says: " One of the most remarkable forms of this revival of Lamarck- ism is the establishment in America of a ' Neo-Lamarck- ian School,' which includes among its members many of the most distinguished American biologists. One of the arguments upon which the founders of the school *Proo. A. A. A. S., 1889, pp. 27:5-276. Am. Nat. March, 1891, p. 191. t Page 4.S7. 48 CALIFORNIA ACADEMY OF SCIENCK.S. have chiefly relied is derived from the comparative mor- phology of mammalian teeth. The evolution of the various types are believed to be due to modifications in shape, produced by the action of mechanical forces (pressure and friction) during the life of the individual. The accumulation of such modifications by means of heredity explains the forms of existing teeth. " It may be reasonably objected that the most element- ary facts concerning the development of teeth prove that their shapes cannot be altered during the lifetime of the individual, except by being worn away. The shape is predetermined before the tooth has cut the gum. Hence the Neo-Lamarckian School assumes, not the transmis- sion of acquired characters, but the transmission of characters which the parent is unable to acquire!" In replying to the criticism of Mr. Poulton, Osborn says: "To the objection that the teeth are entirely formed before piercing the gum, and that use produces an actual loss of tissue as contrasted with the growth of bone, it may be said that by our theory, it is not the growth itself but the reactions which produce this growth in the living tissue, which we suppose to be transmitted." Osborn also criticises Weismaun's theory as follows; "In Weismaun's variation theory the preponderating influence must be conservative; however it may explain progressive modification, or even correlation of old char- acters, it does not admit that the genesis of new char- acters should follow definite lines of adaptation which are not pre-existent in the germ-plasma. We find that new characters of the second class do follow such pur- posive or directive lines, arising simultaneously in all parts of the organism, and first a})pearing in such min- ute form that we have no reason to suppose that they can be acted upon by selection. The old view of nature's choice between two single characters, one adaptive, the EVOLUTION OF THE COLORS OF BIRDS. 49 other not adaptive, must be abandoned, since the latter does not exist in the second class." I have attempted to present a fair statement of both sides of the case in this controversy in regard to the in- heritance of acquired characters, and to all of the import- ant arguments which have been adduced both pro and con, illustrated by typical examples. It will be remembered that the scepticism in regard to the possibility of ac- quired characters being transmitted arose from the theory of heredity enunciated by Prof. Weismann. A study of the different theories of heredity disclosed the fact that while Darwin's hypothesis of pangenesis, or any subsequent modification of it, was a merely formal and provisional scheme for explaining the supposed facts of heredity, Weismann's theory of germ-plasm appears to be a speculative deduction from real facts which the facts themselves do not warrant. That consequently, although this theory may be true, it appears rather vis- ionary and certainly should not be unconditionally accepted as true or even as a working hypothesis, unless the facts dependent upon it can be thus best explained. The practice of stretching facts to fit into a theory is a habit which cannot be too strongly condemned. If Weismann's theory of germ-plasm is unproven there is no apparent reason why acquired characters may not be inherited. An examination of the testimony on this point seems to indicate that both sides have cited cases which did not prove their point. Many so-called proofs which have been brought forward by the Neo- Lamarckians in reality prove nothing, but, on the other hand, some of the interpretations of the Neo-Darwin- ians appear forced and illogical. It is obvious that a single established case of inherit- ance of an acquired character would be sufficient to prove the principle, however many other cases might be dif- 4 50 CALIFORNIA ACADEMY OF SCIENCES. ferently explained. And it seems to me that some fairly well established, if not absolutely convincing, cases have been adduced. Furthermore, the Neo-Dar- winians maintain the illogical assumption that the changes which are observed in the individual have no possible causal connection with the changes which take place in the race, this assumption being contradictory to the law of correspondence of the ontogenic and phylo- genic series. Lastly, it is impossible to explain, from the Neo-Darwinian point of view", simultaneous varia- tions of an adaptive nature. From all this we may come to a provisional conclu- sion that acquired characters are transmissible. We are justified in using this assumption as a working hypothesis, and in feeling confident that future investi- gation will place it upon a footing where it is beyond the possibility of refutation. VARIATION AND NATURAL SELECTION. The end of science is the establishment of natural law, which is merely the orderly relationship existing between phenomena, and consequently cannot be con- sidered as an ultimate cause. Thus gravitation is merely a name for the observed relation between bodies, but does not in any way tell us why these relations exist. Evolution is a term expressive of change in form, and modern biology is striving to determine the precise laws conditioning such changes as occur in organic beings. There are two sets of changes — ontogenic and phy- logenic. It has become the fashion of late years among certain scientists to attribute changes of the second class solely to the action of natural selection, and it thus becomes necessary in inquiring into the laws of evolution to consider first this principle, and de- termine what it can effect. EVOLUTION OP THE COLORS OP BIRDS. 51 It will be necessary to understand clearly the scope and meaning of the term natural selection, or Darwin- ism, as it is frequently called in recognition of its enun- ciator, before inquiring into what it can accomplish. Darwin himself used the term in two different senses, more narrowly as synonymous with Spencer's term sur- vival of the fittest and in the broader interpretation of the cause of modifications including the facts of varia- tion. In this latter application, however, it is inac- curate and misleading. Indeed, the process, is as a rule, not one of selection, as Lloyd Morgan has pointed out,* but rather of rejection, in which case natural elimina- tion becomes a more correct term. But how can any •change be brought about in a species by this process? Prof. J. G. Schurman in a chapter on the Metaphysics of Darwinism! writes as follows of natural selection: " There have been objections to the theory, especially to the somewhat startling assumption that the results of man's purposive selection in breeding could be attained and that, too, on a much larger scale — by the blind and purposeless operations of nature; but granting all that the hypothesis requires of us, we are still in presence of the fact that natural selection, or survival of the fittest, can accomplish nothing until it is supplied with mute- rial for ' selection,' until there has appeared upon the field an antecedent 'fittest' — a fittest organ, function, habit, instinct, constitution, or entire organism. Natu- ral selection produces nothing; it only culls from wha,t is already in existence. The survival of the fittest is an eliminative, not an originative, process." So obvious is the above assertion that it needs no dis- cussion. A variation must be originated before it can * Animal Life and Intelligence, p. 79. tThe Ethical Import of Darwinism, pp. 77-78. 52 CALIFORNIA ACADEMY OF SCIENCES. be selected. We find then, that before variations can occur in the phylogenic series they must take place in the ontogenic series, or in other words, natural selection is strictly conditioned upon individual variation. It therefore becomes a matter of no small moment to en- quire into this subject, from the standpoint of observa- tion to determine what are the possibilities of variation, and from the theoretical aspect to establish the condi- tions of variation. Wallace, more than any other scientist, probably, has given attention to the record- ing of individual variations, and his most recent work, Darwinism, furnishes us with a large number of facts of this sort. An inspection of the instances there given* and of cases adduced by other writers, as Semper in his Animal Life, discloses the fact that they are all quanti- tive and not qualitative. Variations may occur in size, in shape, in position, in number and in color. Varia- tions in size are most numerous and most marked, per- haps, but such variations if in any special direction entail variations in shape. Variation in the position of parts is almost equally great, perhaps, although less readily observed and consequently less frequently re- corded. Variations in number may be trivial and unnoticeable, or may become monstrous as with six- fingered men and two-headed calves. Besides the above mentioned deviations I know of none, except the occasional suppression of parts, either internal or external. The above variations might at first sight appear suf- ficient to produce changes in structures already in ex- istence, but the old difficulty still remains of accounting for the origination of new parts. Wallace's answer to this is certainly apologetic. t Have we a right to assume * Darwinism, pp. 41-82. U. 0., pp. 128-131. EVOLUTION OF THE COLORS OF BIRDS. 53 that variations occurred in past geological ages different in nature from those which occur to-day? If we do not do so, from which class of the variations above enumer- ated were feathers evolved, or horns, for example? Singularly enough, Wallace, an avowed opponent of Lamarckianism, triumphantly appeals to the principles of use in the one difficult variation which he does really explain, the shifting of the eye of the flatfish.*' If in- dividual variation does not normally originate new parts, such as horns, for example, and I know of no reason either theoretical or practical for assuming that it does, then there must be some other factor occasionally called into play; but if some factor exists which must be opera- tive at rare intervals it is but reasonable to assume that it is constantly operative to some extent rather than to suppose that it is lying idle until natural selection is obliged to call upon it to lend a helping hand. The above considerations lead to another frequently urged difficulty that even supposing the necessary varia- tions did occur, we are obliged to assume that they were advantageous. That incipient modifications of an organ- ism are always advantageous is considerable of an assump- tion. It seems incredible, indeed, that some very pro- nounced distinctions can be of utility. Thus it seems difficult to explain, by utility or adaptation, the fact that in California a species of magpie is found identical with the one found east of the Sierra Nevada Mountains, with the exception of being smaller and having the bill bright yellow instead of black. The birds are well isolated geo- graphically throughout the greater part or the whole of their range, so the difference could hardly be accounted for by the theory of recognition markings. This is but one of a great number of instances of a similar nature *1. u., pp. 129-130. 54 CALIFORNIA ACADEMY OF SCIENCES. which might be adduced. Examples of insular species are especially noteworthy in this regard. Mr. Romanes has considered these difficulties at some length in a book which has but just appeared.* The Duke of Argyll in advocating design in nature, made use of the above objections to natural selection, and it is to him that Mr. Romanes addresses his reply. It is hardly necessary to say that the difficulties above stated were not mentioned with a view to show the necessity for design in nature, or some direct supervising power to control the origination of variations, but merely to call attention to the proposition that natural selection, with the help of purely fortuitous variation, does not seem sufficient to account for all structural and specific details. Mr. Romanes, in his reply to the Duke of Argyll, shows how careful it is necessary to be in any particular instance in saying that a character is of no use. Thus the eye inust have been of use in its most incipient stages as a black pigment spot which indicated vaguely the presence of light to the nerves in its vicin- ity. The wing in its incipient stages must also have been of use, as Mr. Romanes points out. Even if a variation were of no use at first it might be indirectly preserved by natural selection through correlation of growth. " Mr. Darwin, who has paid more attention to this matter than any other writer, has shown, in consid- erable detail, that all the parts of any given organism are so intimately bound together, or so mutually dependent upon each other, that when one part is caused to change by means of natural selection, some other parts are very likely to undergo modification as a consequence." The theories which have been put forth to explain variation are, for the most part, very incomplete. Darwin * Darwiu and After Darwin. I — The Darwinian Theory, pp. 350-373. EVOLUTION OF THE COLORS OF BIRDS. 55 freely confesses his ignorance on this point, saying: " Our ignorance of the laws of variation is profound. Not in one case out of a hundred can we pretend to as- sign any reason why this or that part has varied."* Spencer suggests a number of causes for variation. f He considers the influences of environment in altering functions to be one factor in determining variations, e asserting * * * " that organisms produced by th same parents at the same time, must be more or less differentiated both by insensible initial differences, and by slight differences in the conditions to which they are subject during their evolution." He then appeals to first principles to show that no two parts of a homogeneous substance can be exactly alike, and that consequently there must always be a difference at least in the number of physiological units composing a reproductive cell. Thus we have a clue to the differences existing in the young of a single litter. Weismann's theory of variation is probably the most carefully worked out in its details, and is perfectly con- sistent with his theory of the isolation of the germ plasm. It appears impossible, however, that any progressive modification could take place according to this view, for it depends exclusively upon the number of ahnenplas- mas of each sex which enter into combination, this number being largely determined by the amount of sur- plus germ plasm which is disposed of in the extrusion of the two, polar cells. But variation according to this theory, it would seem, must be strictly conservative, for all modifications must be within the extremes of an- cestral modification. Thus, let us suppose that every living individual of some species has been measured, and that 500 represents the number of units in the * Origin of Species, p. 73, Humboldt. tPrinoiples of Biology, I, pp. 257-272. 56 CALIFORNIA ACADEMY OF SCIENCES. smallest individual of the species, and 550 in the largest. There could be, then, no variation due to sexual admix- ture which fell below 500 or rose above 550, and hence no progress would be possible. Another difficulty in Weismann's theory of variation has been recently communicated to Nature, by Prof. Marcus Hartog.* He argues from the assumption that Weismann's theory is proved, and the result is, as he says, indeed a startling one. He first presents five theses expressing the main assumptioias of Weismann's theory, which Poulton has since admitted to be an impartial and correct statement of the case. They are as follows: " I. Each primitive germ-cell of either sex, contains a number of ancestral germ-units, the ahnenplasmas; and this number is constant, for the species at least. II. These ancestral germ-units are far more con- stant and unchangeable in character than the species itself. III. They lie associated together in the germ-cell without loss or alteration of their individual peculiar- ities. IV. The number contained in the mature ovum and spermatzoon is reduced by one-half, and in the fertilized ovum or oosperm the number is restored to the normal by the summation of the ahnenplasmas of the two fusing cells. This process is comparable to the shuffling of two packs of cards by taking half from each and joining the talons or remainders to form a new pack. V. The possible combinations under this process are so numerous as to explain the variations among the offspring of sexual union. Accepting these statements, we next inquire, How 'Nature, October 29, 1891, p. 613. EVOLUTION OF THE COLORS OF BIRDS. 57 are we to conceive of these ancestral units, the ahnen- plasmas? Two hypotheses may be given in answer to this question: A. Each ahneuplasma unit corresponds to an in- dividual of the species itself; and if put under proper tropic conditions, would, singly, reproduce such an in- dividual. B. The ahnenplasmas correspond to the primitive Protozoan ancestors, which, according to theory, could alone reproduce modifications due to external causes (acquired modifications)." Prof. Hartog then shows that if hypothesis A be ac- cepted the ahnenplasmas must have varied with the race, but this would make the shuffling process super- fluous as an explanation of variation, and would also be contradictory to thesis II. "According to hypothesis B," he continues, " the ahnenplasmas of all Metazoa being similar and Proto- zoan, if the numbers are equal and the shuffling fair, any two parents may beget any offspring whatever; on the plane of thesis V, a lioness might be expected to bring forth a lobster or a starfish or any other animal, which as we know, does not take place in nature. The only escape from this result is to assume the postulates — (1) that the number of ahnenplasmas varies from species to species; (2) that the number in the combination and not the character of the ahnenplasmas determines the species. And as there is not a particle of evidence for the latter postulate, we may say that on hypothesis B, the theory breaks down by its non-conformity with the facts. We have then the dilemma, from which I see no escape, that the theory is inconsistent, on A with itself, on B with the facts." It is too soon to attempt to pass judgment upon this 58 CALIFORNIA ACADEMY OF SCIENCES. objection, as the subject is still under discussion. Cer- tain it is, however, that the replies which have been made by Poulton and Trow are incorrect and Hartog demonstrates their inconsistency with the views of Weis- mann by a letter from that gentleman. Lloyd Morgan suggests as an hypothesis of variation a modification of Spencer's theory of physiological units, which has much to commend it, viz., the organic com- bination of the elements of the two sexes into a specific- ally new compound. Morgan explains the need of this hypothesis as follows:* " * * * if, in sexual union, there is a mere mixture, a mere commingling of heredi- tary characters, it is quite impossible that new characters should result, or any intensification of existing charac- ters be produced beyond the mean of those of ovum and sperm. * * * Let us suppose, for the sake of illus- tration, that a pair of organisms have each an available store of forty units of growth-force, and that these are distributed among five sets of organs, a to e, as in the first two columns. Then the offspring will show the organs as arranged in the third column. -Parents . Offspring. . .10. .10 .10. 9 5 7 9. 8 6. 6 40 40 40 " There is no increase in the set of organs a, which are strongly developed in both parents; and no decrease in the set of organs e, which are weakly developed in both parents. By sexual admixture alone there can be no increase or decrease beyond tlie mean of the two ' Animal Life and Intelligence, pp. 150, 151. a. . .10. b 8. c . . 9. ed by the choice of the female bird, are a positive advantage to the species, reducing the numbers of the predominant sex, and their preser- vation is thus insured by natural selection (Stolzmann); in many cases the female bird inherits the bright colors of the male, but these colors are more frequently sup- pressed by the action of natural selection, from the greater necessity for protection on the part of the female during the process of incubation (Wallace). According to the view thus summed up, each one of the investigators who have contributed to the subject have presented only a portion of the truth and have attempted to make it stand for the whole. This synthe- sis seems to satisfy all the various objections which have been raised against sexual selection, and to supply a tol- erably complete explanation of secondary sexual char- acters in birds. EVOLUTION OF THE COLORS OP BIRDS. 103 THE NATURE OF SPECIES. Throughout all the foregoing consideration of the various theories and speculations regarding the factors of organic evolution, it will be noticed that little has been said about the nature and origin of species. This has been left for the conclusion, as the final problem for evolution to solve. In the first place, a few words on the term species will be necessary. In its broadest or logical interpretation, any set of individuals having some characteristic or group of characteristics in com- mon, constitutes a species. Species may be determined upon an artificial or upon a natural basis. For example, the human race might be divided into species depend- ing upon the occupation pursued, when we would have a species of hunters, a species of mechanics, one of doctors, another of lawyers, and so on, ad infinitum.. This would, indeed, be, to a certain extent, a natural classification, from one point of view. Or we might divide mankind more arbitrarily into species according to height, weight, disposition, or attainments, which would be a classification into artificial species. A natural system differs from the foregoing in showing real rela- tion through common ancestry. To be sure, in the classification of the human race according to occupations, a true relation through common ancestry is shown, for the progenitors of the human race undoubtedly all had much the same occupation, from which all subsequent pursuits have been evolved; but a natural system of division must do more than indicate a real connection by evolutionary succession — it must show that partic- ular connection or group of connections which is most vital to the nature or being of the thing classified. In fact that which is used as a basis for a natural classifica- tion must be that which is most fundamental to the being classified, and each stage in division must be based 104 CALIFORNIA ACADEMY OP SCIENCES. upon that quality or property which most vitally con- ditions it, and is common to all subsequent groups which may be contained within it. To illustrate: A natural classification of man must be based upon life, which, from a scientific point of view at least, is the most A'ital and fundamental property of the being under consideration. The next stage in the classification would be a division into the animal and vegetable life, and the third the placing of man in the vertebrate series of animals. It will be observed that this third proces^^ of division is simply a particular form of the funda- mental property with which we started. Continuing in this same manner, we should ultimately get a classifica- tion of men into the various races, Caucasian, Ethio- pian, jMongolian, etc., and a subdivision of each of these into the various trilius or nationalities, as Ger- mans, French, Italians, Americans. It is possible to go even a stage farther, and divide Americans into Yan- kees, New Yorkers, Southerners, etc., but a point is ultimately reached where no further division is possible because no characteristic can be found of any number of individuals which is a more special expression of some more universal and necessary property of their being. The point to be emphasized in this discussion is the fact that logically any group, however extensive or re- stricted, may l>e regarded as a species in relation to the next more inclusive group which contains it, and con- stitutes its genus. Thus, logicalh', the vertebrates form one species of the genus animal. Furthermore, science is more or less arbitrary in the making of species, unless only the most ultimate and special division of a group be considered as such. Such a distinction of si3ecies is never made, however, for what scientist would ven- ture to make the Yankee a distinct species, mucj'icnnus, EVOLUTION OF THE COLORS OF BIRDS. 105 of the genus Homo, even though every individual had a nasal twang which unerringly indicated the section from which he came? The Code of Nomenclature of the American Ornithologists Union* contains the following apt sentences on this subject: "There is no inherent zoological difference between a ' generic ' and a ' specific ' name, — the nomen genericum and the nomen triviale of earlier zoologists. Both alike designate a 'group' in Zoology, — the one a group of greater, the other a group of lesser classificatory value. Some necessary distinction, which has been misconceived to exist between these two names, is simply a fortuitous matter of the technique of nomenclature, apparently arising from the circumstance that the generic and the specific names form the con- trasted though connected terms of a binomial designa- tion. Recognition of the scientific fact, that a 'species,' so called, is not a fixed and special creation, as long supposed, but simply a group of the same intrinsic character as that called a ' genus,' though usually less extensive, and always of a lower taxonomic rank, has done more than a&y other single thing to advance the science of Zoology; for the whole theory of evolution turns, as it were, upon this point." From the above it is apparent that the decision of whether any particular group of individuals constitutes a species or some greater or lesser taxonomic division, must be more or less arbitrarily settled. In general, however, it may be said that a species in science is a group of individuals morphologically isolated from every other group by at least one peculiar character.! Wherever a group is not completely isolated, but con- nected by living intervening forms with some other * pp. 26 -27. t The word ^norphological is here used in its broadest interpretation, as distinguished from physiological, and of course includes color changes. 106 CALIFORNIA ACADEMY OF SCIKNCES. group, it is called a variety. Species anJ varieties, then, do not always represent real taxonomic values, for two extreme varieties of one species may be morphologically very much less alike than two closely allied species. It all depends upon the accident of destruction of inter- mediate forms. Having now clearly defined the nature of a species and the relativity of its value, it is time to consider the relation of evolution to species. The end of evolution is the establishment of successively higher types. Pro- gress must be orderly, and species are merely crystal- lized forms of orderliness. If each individual were to start off on its own independent track there would be no unity in nature. Organisms would not hold together, and life as a whole would present no feature of ration- alit}'. Real progress would be defeated, and evolution would end in chaos. But in recognizing that species are the indispensable instruments of orderly evolution, is it necessarily implied that species are the outcome of natural selection? This implication certainly does not inevitably follow, even using the term natural selection in its widest sense, and admitting it as an important factor in evolution. Before considering this fundamental question as to whether or not natural selection, aided, of course, by all the factors of hereditj' and variation, can originate species, it will be well to enquire what it is that natural selection preserves — the individual or the species. Mr. Romanes, in the Darwinian Theory* says: "Next, it must be clearly understood that the life which it is the object, so to speak, of natural selection to preserve, is primarily the life of the sjtccie!<; not that of the indl- vitlual. Natural selection preserves the life of the individual only in so far as this is conducive to that of ' Darwin and After Darwin, i, pp. '2C4-2(J.''i . EVOLUTION OP THE COLORS OF BIRDS. 107 the species. Wherever the life-interests of the individ- ual clash with those of the species, that individual is sacrificed in favour of others who happen better to sub- serve the interests of the species. For example, in all organisms a greater or less amount of vigour is wasted, so far as individual interests are concerned, in the form- ation and the nourishment of progeny. * * * *■ Again, all unselfish instincts have been developed for the sake of the species, and usually against the interests of the individual. An ant which will allow her head to be .slowly drawn from her body rather than relinquish her hold upon a pupa, is clearly acting in response to an instinct which has been developed for the benefit of the hive, though fatal to the individual. And, in a lesser degree, the parental ins^ncts, wherever they occur, are more or less detrimental to the interests of the individ- ual, though correspondingly essential to those of the race." Let us view these words of Mr. Romanes in the light of what has just been said concerning the nature of a species. Discarding any teleological conception as un- worthy of scientific consideration, why should natural selection preserve the species rather than any other more or less inclusive taxonomic group? Natural selection is the result of a struggle for existence. This struggle for existence, as Darwin has shown, is most keen among those individuals that are most alike; just as among men, doctors come into closer competition with one another than they do with lawyers, or a dry goods mer- chant will have a harder contest with his fellow dry goods merchants than he will with a hardware merchant. The struggle for existence is then, first of all, a struggle of individuals of one species among themselves, in which battle only the fittest will survive. But how could the self-sacrificing ant to which Mr. Romanes alludes. 108 CALIFORNIA ACADEMY OF SCIENCES. pass muster in such a struggle for existence of individ- ual with individual; or how could any altruistic trait be evolved? Mr. Romanes, it seems, has not adequately shown this. The parental instinct does not constitute a strictly corresponding instance, for the survival of the fittest must of course mean the survival of those indi- viduals best fitted to leave offspring. In the case of the dry goods merchant just referred to, he would only be the fittest individual to survive in the long run, if he were able not merely to win his place among his com- petitors, but to maintain it through his heirs. Repro- duction is merely growth beyond the individual, and accordingly the longer the line of potential descendants which an individual leaves, the longer will that indi- vidual survive, speaking broadly. Consequently, no sexual individual is really complete. It can only be- come complete by perpetuating itself, Avhich demands a mate. In this view of reproduction a clue may be found to the introduction of altruistic traits. Every individual's bodily immortality is conditioned by the existence and well being of some other individual. The survival of the individual is thus clearly wrapped up with the sur- vival of the family, and natural selection Avould there- fore encourage any tendency which would promote the family, even to the disadvantage of certain members of it. Thus the habit of feigning lameness by some birds to lure an enemy from the young, is a source of danger to the parent but a protection to the young. If in any case, however, the danger to the parent were greater tlian the protection to the young, the habit could not have been acquired, for whenever the parent were lost through the exorcise of this altruistic habit, the young would in the great majority of cases die of neglect, and the habit would not become estal)lished. EVOLUTION OP THE COLORS OF BIRDS. 109 To admit that it is the family rather than the single individual which natural selection preserves, is far dif- ferent from granting that the species, or even the race or tribe is what natural selection especially favors. Let us pass on next to a consideration of this point. The family, as we have seen, is absolutely indispensable to the life of the individual, in the widest sense, but this is not the case with the tribe. The individual can have a potential bodily immortality without the tribe, and in a large number of cases this actually occurs. However, it sometimes happens that by associating in a community with similar interests, a greater number of individuals can enjoy an immunity from some common danger. This would only occur when the struggle for ex- istence was more severe with some outside enemy than with each other, which would be a comparatively exceptional state of affairs. This has not brought us any nearer to Mr. Romanes' main proposition, that it is the life of th-e species which natural selection preserves, and not that of the indi- vidual. In point of fact, natural selection does not preserve species with anything like the persistence with which she perpetuates genera, nor are genera as lasting as orders. What natural selection really pre- serves are those individuals which are capable of perpet- uating something higher or more perfect. A species is an aggregate of individuals in which some new feature of excellence is universally present, and from the very fact of their'possessiiig this new feature they will stand a better chance of being preserved as a whole, than another group of individuals which lack this higher or advantageous characteristic. To return to the analogy of the dry goods merchants, which, by the way, is a true analogy because natural selection is actually in operation in this instance: their struggle for existence, 110 CALIFORNIA ACADEMY OF SCIENCES. as previously pointed out, is more intense among them- selves than it is with the hardware or shoe merchants. Now, if in some large city, a portion of the dry goods merchants should introduce some new feature, such as keeping open evenings and lighting their stores with electricity, while the other dry goods merchants were unable to afford this innovation, a new species of dry goods store would arise, every individual of which would be at an advantage over the old species. The struggle for existence would then go on between the dif- ferent individuals of the new species and those who were able to afford the most brilliant illumination or to keep open the longest would survive, while the others would die. In this sense natural selection is protecting the species regardless of the individual, but in a deeper sense it is protecting the individual regardless of the species. PHYSIOLOGICAL SELECTION. Mr. Romanes has also raised the deeper question, has natural selection, even in its widest sense, originated all new species? His original paper on Physiological Selection was read before the Linnean Society, May 6, 1886,* and shortly afterwards an abstract appeared in the columns of Nature. This communication aroused a great storm of opposition, Wallace in particular enlist- ing himself with the enemy. Romanes asserts that there are three cardinal difficulties in the way of natural selection, considered as a theory of the origin of species. These are: (1) the difference between species and vari- eties in respect of mutual fertility; (2) the swamping effect of free intercrossing upon an individual variation; and (3) the inutility of a large number of specific char- acters. ' .Jouru. Linn. Soc. xix, pp. 337-411. EVOLUTION OF THE COLORS 01' BIRDS. Ill To overcome these three difficulties he has proposed a new factor, physiological selection or the segregation of the fit. It is a known fact that isolation favors the production of new species. Oceanic islands in partic- ular attest to this. According to Mr. Romanes, how- ever, the advantage of geographical isolation is not always offered to incipient species, which often branch off in the midst of the parent stock. It is a noteworthy cir- cumstance, however, that of all parts of an organism the reproductive organs are most susceptible to change, and if a variation in these parts should occur among a number of individuals making them sterile with the rest of the species but fertile among themselves, they would be physiologically isolated even in the midst of their associates. In the words of the author, this view enables us to regard many, if not most, natural species as the records of variation in the reproductive systems of ancestors. In considering the three difficulties in the way of natu- ral selection the author adduces considerable evidence to show that the difficulties are real. He asserts that the fundamental or primary difference between species is sterility, this being a common distinguishing feature in nearly every instance. Other differences consist in innumerable distinctions of structure, color or markings, which he calls secondary differences. Inasmuch as these secondary differences are never exactly alike in two species while the primary difference is always the same, he demands an explanation of the constancy of this distinction, asserting that all previous theories have dealt only with the secondary differences. Even where geographical isolation has originated species it is not possible to account for the almost universal sterility existing between them. " The consequence is," he says, " that most evolutionists here fall back upon a 112 CALIFORNIA ACADEMY OF SCIENCES. great assumption: they say that it must be the change of organism which causes the sterility — it must be the secondary distinctions which determine the primary. But the contrary proposition is surely at least probable, namely, that it is the sterility which, by preventing inter- crossing with parent forms, has determined the sec- ondary distinctions — or, rather, that it has been the original condition to the operation of the modifying causes in all cases where free intercrossing has not been otherwise prevented." The author then proceeds to show that it is not logical to suppose that any one of so infinite a number of changes could have the same effect in modifying the reproductive system. Further- more, these changes constantly occur among domesti- cated animals without affecting the fertility of the breed. Darwin has shown that among wild species the ratio between structural affinity and the degree of ster- ility is not always constant, some very distinct species being found to hybridize with facility; but this is not in accord with the view that the sterility is universally due to structural differences. "Mr. Darwin further shows that, ' independently of the question of fertility, in all other respects there is the closest general resemblance between hybrids and mongrels.' Clearly, this fact implies that natural selection and artificial selection run perfectly parallel in all other respects, save in the one respect of reacting on the reproductive system, where, according to the views against which I am arguing, they must be regarded as differing, not only constantly but also profoundly. Lastly, Mr. Darwin concedes — or rather insists — that ' the primary cause of the sterility of crossed species is confined to differences in their sexual elements.' A general fact which assuredly proves that the primary specific distinction is one with which the organism as a whole is not concerned: it is merely a EVOLUTION OF THE COLORS OF BIRDS. 113 local variation which is concerned only with the sexual system. Why, then, should we suppose that it differs from a local variation taking place in any other part of the organism? Why should we suppose that, unlike all other such variations, it can never be independent, but must always be superinduced as a secondary result of changes taking place elsewhere?"* After stating at length his reasons for believing that variations in the reproductive system may arise inde- pendently of variations in the organism, Mr. Romanes qualifies this by admitting that in some cases the varia- tion in the sexual organs may be correlated with other variations in the system, and may have been primarily caused by natural selection; but in granting this he shows that natural selection simply becomes one of the causes determining physiological selection. " If," he says, "we thus regard sterility between species as the result of what I have called a local variation, or a varia- tion arising only in the reproductive system — whether this be induced by changes taking place in other parts of the organism, to changes in the conditions of life, or to changes inherent in the reproductive system itself — we can understand why such sterility rarely, though some- times, occurs in our domesticated productions; why it so generally occurs in some degree between species; and why as between species it occurs in all degrees." As to the evidence of this infertility between indi- viduals of the same species, which is a necessary assumption of the theory, many cases of failure to interbreed have been adduced by Darwin and others. Or the time of flowering or mating may be accelerated or retarded in certain individuals, thus isolating them from the rest of the race. * Nature xxxiv, pp. 338-339. 8 114 CALIFORNIA ACADEMY OF SCIENCES. The second difficulty of the doctrine of natural selec- tion as the originator of species, according to Mr. Ro- manes, is the swamping effect of interbreeding. AVherever any geographical barrier cuts off a portion of a race the section so isolated is found to develop into a new species. In fact, it is evident that if occasional variations arise in individuals in the midst of others in which they do not occur, they will soon be eradicated by interbreeding with the dominant class, however ad- vantageous they might be. Physiological selection would of course prevent this. Mr. Romanes' third difficulty is a question of fact. Are all specific characters useful? Natural selection concerns itself solely with adaptations caring nothing whatever for species as such. In case the specific char- acter is also an adaptive character, it is reasonable to suppose that it has been developed by natural selection; but if, as Mr. Romanes contends, a large number of specific characters are of no use, some other factor must have developed them, which factor Mr. Romanes consid- ers to be physiological selection. He asserts, moreover, that without isolation evolution would be linear in direction but never branching. The struggle for exist- ence is most intense in the most populous districts, and consequently the evolution of new species should be most rapid in such regions, but the evolution of new forms in a crowded district would be especially difficult, in fact practically impossible without some form of iso- lation. Physiological selection would afford this needed aid. That so revolutionary a theory as this appeared to be should not be immediately accepted by scientists was not to be wondered at. To be sure it had been sug- gested previously in Mr. Belt's Nicaragua and in a letter to Nature by Mr. Catchpool, but Mr. Romanes EVOLUTION OF THE COLORS OF BIRDS. 115 for the first time elaborated it and pointed out some of its bearings upon the doctrine of natural selection. Mr. E,. Meldola was one of the first critics of the new theory.* He asserted that the principal difficulty pointed out by Mr. Romanes was " the sterility of natural species as compared with the fertility of domesticated races." In- asmuch as the struggle for existence is most intense between those individuals which are most alike, any- thing which would cause them to vary would be an advantage which natural selection would make use of. The prevention of intercrossing by inter-sterility would be such an advantage and natural selection would accordingly favor it. Mr. Francis Galton, soon after offered another sug- gestion regarding physiological selection.! According to his view certain individuals of a race are isolated from the rest by having similar sexual likes and dislikes which cause them to interbreed rather than to mingle with the rest of the tribe. In replying to the above two criticisms, Mr. Eomanes attempts to show that neither Galton nor Meldola have really opposed his views. Mr. Galton had objected to physiological selection on the ground that the intersterility which it presupposes would not be externally apparent, and consequently many in- fertile unions would result. There is nothing to show, however, that infertile unions do not take place at times, and Mr. Galto.n's hypothesis of psychological selection simply supplements among the higher animals the more universal factor of physiological selection. In replying to Mr. Meldola's criticism, Mr. Romanes shows that it is not his theory of physiological selection which is called in question, but simply whether natural selection may not in every case underlie and condition * Nature xxxiv, pp. 384-395. 1 1.0. pp. 395-396. 116 CALIFORNIA ACADEMY OF SCIENCES. it. " But surely," he says, "the burden of proof here lies on the side of my critic. If he can show any suffi- cient reason for going much farther than I have ventured to go in out-Darwining Darwin — or for holding that natural selection may not merely help in inducing ster- tlity in some cases, but has been the sole cause of it in all cases — then I should welcome his proof as showing that the principles of physiological selection ultimately and in all cases rest on those of natural selection. But, clearly, it is for him to prove his positive: not for me to prove what I regard as an almost preposterous neg- ative."* Mr. Meldola also noted the difficulty that physiologi- cal selection must always be subservient to natural selection, because if a race developed through isolation did not possess some advantage over the main stock — the struggle for existence being most severe among most closely related forms — it would not be able to compete with the dominant type of the species. In reply to this Mr. Romanes states that if the character distinguishing the new form be indifferent as regards utility the in- dividuals possessing it will be on an exactly equal foot- ing with those which do not possess it, more especially if as at first, the variation be simply of the reproductive organs. The fact that the individual possessing this variation has reached the breeding age is in itself a guarantee of its fitness to survive, and it was to empha- size this fact that the alternative name of the " segrega- tion of the fit" was proposed. Mr. Wallace has however presented a more sweeping and serious line of criticism than any of the preceding, audit is to this that attention must next be directed. His objections were stated in an artide entitled "Romanes versus Darwin. An Episode in the History of the *1. c. p. 408. EVOLUTION OF THE COLORS OF BIRDS. 117 Evolution Theory."* Mr. Wallace objects most em- phatically to the view that any specific characters are without use. He points to the progress which has been made of late years in discovering the use of structures or characters which were formally thought to be of no utility, and calls particular attention to the colors of the higher vertebrates as illustrating his point. He men- tions the fact that while the colors of wild animals are so generally constant (white or pied varieties being speedily obliterated) domestic breeds exhibit the greatest inconstancy and diversity in this respect; proving, as he thinks, that the colors of all wild animals must be useful, even though we cannot always see how they are so, and that their lack of uniformity under -domestica- tion is due to the fact that they are no longer of utility. He then gives illustrations of the various forms of adaptive markings — protective and warning colors and recognition markings. He says: " This need of easy recognition by each species of its own kind and of the sexes by each other, will probably explain at once those slight diversities of colour and marking, which, more commonly than any other characters distinguish closely allied species from each other, and also the constancy and bilateral symmetry of the colouration of wild ani- mals." With regard to the swamping effects of free intercross- ing, Mr. Wallace says the difficulty is removed by con- ceding "that the same variation occurs simultaneously in a number of individuals inhabiting the same area." Mr. Romanes had denied this, but Mr. Wallace presents an array of facts taken from Mr. J. A. Allen's Winter Birds of Florida, in support of his contention. So far as the infertility of species with one another is concerned, Mr. Wallace denies that the facts support ■"Fortnightly Eeview, xlvi, jip. 300-316. 118 CALIFORNIA ACADEMY OP SCIENCES. Mr. Romanes' side of the argument. He points out that experiments in hybridizing are generally made with very distinct species, and that even these are some- times fertile, while if two closely related forms hybridize they are said to be one species. He quotes Dean Her- bert's experiments as proving that in several large genera of plants not only are the hybrids often fertile but sometimes more so than the parent stock, whence he concludes "that the sterility or fertility of the offspring does not depend upon original diversity of stock; and that if two species are to be united in a scientific arrangement on account of a fertile issue, the botanist must give up his specific distinctions generally, and intrench himself within genera." " Really close species," says Air. Wallace, " which have probably originated by one remove from a common an- cestor have never yet been crossed in large numbers and for several generations, under appropriately natural con- ditions, so as to afford any reliable data. The mere fact that not only animals of distinct genera, but even those classed in distinct families — as the pheasant and the black grouse — sometimes produce hybrid offspring in a state of nature, is itself an argument against there being any constant infertility between the most closely allied species, since if that were the case we should expect the infertility to increase steadily with remoteness of descent till when we came to family distinctions absolute sterility should be invariable." To these criticisms of Mr. Wallace, Mr. Romanes replied in an article in the Nineteenth Century,* enti- tled Physiological Selection. He freely grants that Mr. Wallace has proved that some specific characters are useful, but insists that this is not sufficient to prove that all points of specific difference are so. The theory of 'xxi, pp. .51I-.SI). EVOLUTION OJ? THE COLORS OF BIRDS. 119 natural selection is based upon the assumption that cer- tain characters are useful, but we are not justified in arguing from this that all characters have been devel- oped by natural selection and are therefore useful. Darwin himself freely conceded the inutility of many characters, and, as Mr. Eomanessays, " there is positive evidence to show that the slight changes of form and colour which chiefly serve to distinguish allied species are often due to what Mr. Darwin calls ' the direct action of external conditions,' such as changes of food, climate, etc., as well as to mere independent variation on isolated areas, and in some of our domesticated pro- ductions, etc.; and in none of these cases do the specific changes which result present a meaning of any kind." In refuting Mr. Wallace's argument on the utility of color Mr Romanes, in a footnote, quotes Darwin to the effect that "each of the endless variations which we see in the plumage of our fowls must have had some efficient cause; and if the same causes were to act uniformly during the long series of generations on many individuals, all probably would be modified in the same manner," and he adds: "The obvious truth of this remark serves to dispose of Mr. Wallace's argument in the Fortnightly, that ' the general constancy of colouration we observe in each wild species,' of itself furnishes sufficient proof that the colouration must be ' a useful character.' Moreover, when using this argument Mr. Wallace forgets that uniformity of colouration (whether useful or unuseful) is preserved in wild species by free intercrossing. Where this is prevented — as by isola- tion or migration — variations of colour very frequently do take place, just as in the thenanalgous case of our do- mesticated strains." Concerning the swamping effects of intercrossing, Mr. Romanes shows that the variations cited from Mr. 120 CALIFORNIA ACADEMY OF SCIENCES. Allen's paper as quoted by Wallace would not be suffi- cient to originate any new structure. He says: " It is easy to see how natural selection eould alter the general size of the body, the relative sizes of parts, degrees of colouration, etc., without encountering any great diffi- culty from intercrossing. But if it were required to produce, say, a fighting spur on a duck, clearly it could not be done by natural selection alone, or when depend- ing only on ' accidental variations.' " Mr. Romanes has here granted far too much to his critic; for, if physio- logical selection is not a necessary factor in the modifi- cation of size, shape (relative sizes of parts), and color, all closely related species which depend upon such features for their specific identity (and they constitute a very large proportion of species), would be excluded from the operation of the segregation of the fit. Nor would this factor particularly assist in the production of spurs and horns, for example. It is thought by many that such structures are due to the factor of use, in which case physiological selection would indeed become re- stricted in its function. In replying to Wallace's criticisms of his view of sterility between species, Mr. Romanes says: " Under this head Mr. Wallace's criticism amounts to nothing more than a vague suggestion to the effect that all other naturalists may have hitherto exaggerated the generality of some degree of sterility between species. But he allows that it is 'a widespread phenomenon,' and gives no reasons for differing from ]\Ir. Darwin's careful esti- mate of its frequency, he does not really furnish me with any material to discuss." Mr. Seebohni in the introduction to his work entitled The Geogra})hical Distribution of Charadriidiu, also makes a sweeping criticism of physiological selection, and as he and Mr. AVallaco argue on the same lini'S upon EVOLUTION OF THE COLORS OP BIRDS. 121 certain points, it may be well to pass on now to a brief survey of his objections. The central idea of his argu- ment is that variations are never spontaneous, but always due to a definitie cause, so that "the inevitable new species will be produced even in defiance of increased fertility between the diverging forms." He lays great stress upon geographical isolation, however, and doubts that any new species of bird has arisen with- out the aid of this factor. He propounds a rather novel explanation of the mutual infertility of natural species as compared with the fertility of domesticated breeds. Briefly stated it is this: Domestic animals are species which from some unknown reason are capable of adapt- ing themselves to a great variety of circumstances. Just as the individual as a whole is capable of surviving in various environments, so also, it may be supposed, the germ cell of the male of such individuals would have a greater vitality, and would be capable of surviving in an unusual ovarian environment. A proportion is thus established between the individual and its seed — as the stable individual is to the plastic individual so is the reproductive element stable or plastic. He calls atten- tion to the fact that in a state of nature fertile hybrids occur most frequently among the Phasianidce and Anatidce, "the very families to which most of our do- mestic birds belong." This is certainly a very plausible and ingenious theory, and I am not familiar with any attempted refutation. Unlike Mr. Wallace, Mr. Seebohm freely grants that " specific differences are frequently, if not usually, with- out utilitarian significance," but he considers that this is due to the fact that they, have been brought about by definite variation witbout reference either to natural or physiological selection. Upon one point, however, he and Mr. Wallace agree, namely, that granting all that 122 CALIFORNIA ACADEMY OF SCEENCES. physiological selection demands, the chance of all the necessary contingencies arising contemporaneously would be so slight as to make the theory unworkable. Mr. Seebohm says: " To make it work we must pre- suppose: — 1st, the special variation of the reproductive organs must occur in two inviduals, otherwise the pos- sible ancestor of the new species M'ould have no descendants; 2nd, it must occur at the same time in both; 3d, it must occur at the same place; 4tli, the two indi- viduals must be of opposite sexes; 5th, they must each of them possess some other variation, or their progeny would not differ from that of the rest of the species; and 6th, the variation must be the same in both, or appear simultaneously in the majority of their children, other- wise it would be swamped by interbreeding within the physiologically isolated family." Obviously Mr. See- bohm does not think it possible for all these contingen- cies to be realized, and that from their failure to co-operate the theory of physiological selection must break down. Along the same lines as this Mr. Wallace also objects to the segregation of the fit. In reply, Mr. Romanes asserts that while it is true that the chances against these physiologically isolated individuals mating may indeed be thousands to one, so is it also true that the number of fertile unions among animals com- pared to the origination of every new species is in the proportion of thousands to one, and he says: " I con- fess it appears to me a somewhat feeble criticism to represent that the conditions which my theory requires for the origin of a new species are probably about as rare in their occurrence as is the result which they are supposed to produce." He furthermore states that the variations in fertility of the sexual organs are not due to chance, as his critics have assumed. They EVOLUTION OP THE COLORS OP BIRDS. 123 may be due to the change in season of flowering or pair- ing, or to difference in food or climate, or they may even be originated by natural selection itself. Indeed, Mr. Wallace has suggested as an " alternative hypothesis " to physiological selection, that specific sterility is due to a relation existing between the external coloring and sexual compatibility, so that whenever a change in color is produced, the individuals so changed will not be fer- tile with the parent stock. Mr. Romanes clearly shows that instead of being an alternative hypothesis, if tenable at all, it merely furnishes us with an additional indirect cause of the infertility demanded by physio- logical selection. Mr. Romanes gives a number of forcible reasons for not granting this theory the promi- nent function attributed to it by Mr. Wallace. Thus he asserts that "many species which are mutually sterile differ very little in color," while " most species which are mutually fertile differ considerably " in this respect. Furthermore, "in the case of natural species, it often happens that a great difference in respect of fertility occurs, according to which has acted as the male and which as the female, yet in both these crosses the colour of each species is, of course, the same." The controversy which Mr. Romanes had with Mr. W. Thiselton-Dyer, in the columns of Nature in 1889, respecting physiological selection, did not serve to eluci- date many new points. Mr. Dyer's objections to the terms physiological selection and the segregation of the fit, need not here detain us, for Mr. Romanes had previously justified their use. The discussion centered upon the relation between natural and physiological se- lection. Mr. Romanes has so clearly expressed this in an admirable figure that to quote it, will be a sufficient epitome of the argument. He says: " In short, species are like leaves, successive and transient crops of which 124 CALIFORNIA ACADEMY OF HCIENCES. are necessary to the gradual building up of adaptations, while these, like the woody and permanent branches, grow continuously in importance through all, the tree of life. Now, it is the office of natural selection to see to the growth of these permanent branches; physiological selection has to do only with the deciduous leaves." Having now stated the principal arguments for and against physiological selection, with as little bias as possible, it only remains to pass judgment upon their merits. This, however, does not appear to be an easy task; but as usual in such cases, it will probably be found that both sides are partly in the right and partly wrong. Thus, with regard to sterility, natural species are as a general thing sterile inter se, while domestic races are usually fertile, but these conditions are by no means uniformly constant. Physiological isolation might explain this state of affairs, while Mr. Seebphm's hypothesis has quite an aspect of plausibility, — or both views might be correct ; whereas, various secondary factors have been instrumental in bringing about this condition. There seems to be hardly any evidence, however, that sterility with the parent stock is generally one of the first variations of a diverging race, but if this be not so, then the chief aim of the theory — viz. to account for the early stages of divergence — fails. Isolation may be advantageous in preventing the swamping effects of free intercrossing, although Mr. Romanes has granted that the size, shape, or degree of coloration, may be modified without its aid. Further- more, geographical isolation is an ever-present factor, while a slight change in habits on the part of certain individuals would effect their isolation, psychological isolation, as suggested by Galton, may also be a valid factor, while the operation of physiological selection itself need not be excluded. EVOLUTION OF THE COLORS OP BIRDS. 125 Thirdly, some specific characters, at least, are ap- parently of no conceivable use, but these may be due to the direct action of the environment or to the use and disuse of parts. As regards the bearing of the above discussion upon the evolution of the colors of birds, in the light of the evidence adduced, it would hardly seem justifiable to use physiological selection, unless the facts admitted of no other rational explanation. It is always an easy loop- hole for escape in accounting for any difficult character, and for this very reason should be treated with especial caution. GULICK ON ISOLATION. One of the most valuable contributions made of late years to the literature of evolution is the series of articles upon isola*tion by the Rev. J. T. Gulick. His views coincide with those of Mr. Romanes upon many important points, while their theories overlap to a cer- tain extent. Without considering in detail the relation- ship between their respective views, it may be said that they both agree that many specific characters are use- less, and that isolation is a nece^ary factor in their origination, but Gulick does not emphasize physiological isolation as Romanes has done; while he asserts, con- trary to Romanes, that not only species, but larger groups as well require isolation as a factor in their origin. His central idea is this: no two groups of individuals of one species contain exactly the same pro- portion of variations in their aggregate number; accord- ingly, if two or more miscellaneous groups are isolated, inasmuch as free intercrossing is no longer practicable to preserve the average, each division will necessarily start off on an independent line, irrespective of its environment. Futhermore, natural selection without isolation could not produce divergent, but only linear 126 CALIFORNIA ACADEMY OF SCIENCES. evolution. Natural selection implies a contest between a more and less favorable class of variations, in which the less favorable class perish. As an example, a race horse might be evolved by artifical selection from a common stock, but in order to produce a dray horse from the same stock, the two varieties would have to be isolated from the earliest stages of their divergence. The tendency of this view of Mr. Gulick's is to over- estimate the self-sufficiency of the organism to originate new forms by virtue of an assumed inherent tendency to vary indefinitely. In other words, he sometimes appears to assume, in conformity with Nageli, that each organism contains within itself the potentiality of devel- oping all the forms which may be subsequently derived therefrom; that free intercrossing suppresses this ten- dency to vary, but isolation enables each group to develop any little idiosyncrasies toward which it may have a leaning, and by successive stages of isolation these are piled up into new characteristics or structures. Thus, in summing up the result of his survey of the various forms of selection, he finds: *" First, that all the forms of Reflexive Selection are due to the relations of members of the same species to each other, and are liable to change without any change in the environ- ments. Second, that Active Natural Selection is due to change in the successful use of the powers of the organ- ism in dealing with the environment, and is not depend- ent on change in the environment. Third, that Passive Natural Selection, which is due to the exposure of the organism to a different environment, is often produced by the organism's entering a new environment without there being any change in either the new or the old environment. Fourth, that when Passive Natural Selec- * Journ. Linn. Soc. xxiii, p. S.37. EVOLUTION OF THE COLORS OP BIRDS. 127 tion is produced by change in the environment, the more effective forms of Selection do not appear till the organism has so multiplied as to produce what I call Superlative Natural Selection through intense competi- tion between rival individuals of the same species in gaining possession of limited resources. And, fifth, that Passive Comparative Natural Selection, which de- pends on change in the environment, without special rivalry between the members of one species, also depends on variation in the adaptations of the organism, many of which variations do not depend on that change in the environment which has produced the change in the Natural Selection, nor, indeed, on any change in the environment except those physical changes by which the world has passed from its primitive gaseous to its present partially liquid and solid state, rendering it a fit abode for organisms." He thus entirely ignores the origin of variations and assumes that inasmuch as the environment in the vari- ous forms of selection cited does not produce the varia- tions definitely and directly, it can have no influ- ence whatever in their origination. If the discussion of variation in the preceding pages has any force what- ever, this conclusion certainly should not seem an in- evitable one. An attentive consideration of Mr. Gulick's views seems to make one fact undeniable, viz. that some form of isolation is indispensable to divergent evolution. His elaboration of the various forms of isolation is so exten- sive that anything more than a brief outline of it would be impossible in the present connection. This much is, however, necessary to even a general under- standing of the factors of organic evolution. The fol- lowing is Mr. Gulick's classification table of the forms of segregation: 128 CALIBORNIA ACADEMY OF SCIENCES. A. Environal Segregation. (a) Industrial Segregation. Sustentational. Defensive. Nidificational. (b) Ciironal Segregation. Cyclical. Seasonal. (c) Spatial Segregation. ) (Migrational. lllT Transportational. ) (Geological. (d) Fertilizational Segregation. (e) Artifical Segregation. B. Reflexive Segregation. (a) Conjunctional Segregation. Social. Sexual. Germinal. Floral. (b) Impregnational Segregation. Segregate Size. Segregate Structure. Prepotential Segregation. Segregate Fecundity. Segregate Vigour. (e) Institutional Segregation. C. Intensive Segregation. (a) Assimilational Intension. (b) Stimulational Intension. (c) Suetudinal Intension. (d) Correlated Intension. (e) Integrational Intension. (f) Selectional Intension. (g) Fecundal Intension. (h) Eliminational Intension. EVOLUTION OP THE COLORS OP BIRDS. 129 The following brief definitions will explain the above terms: A. Environ AL Segregation — Isolation due to the relations of organism to environment. (a) Industrial Segregation. "Activities by which the organism protects itself against adverse influences in the environment, or by which it finds and appro- priates special resources in the environment." 1. Sustentational. " Different methods of obtaining sustentation by members of the same species." 2. Defensive. "Different methods of protection against adverse influences in the environment." 3. Nidificational. Differences in nesting habits in the same species. (b) Ghronal Segregation. "Segregation arising from the relations in which the organism stands to times and seasons." 4. Cyclical Segregation. Among certain insects "the life cycles of the different sections of the species do not mature in the same years." 5. Seasonal Segregation. Change in time of flower- ing or breeding of a section of a species. (c) Spatial Segregation. Isolation in space. Geographical. Physical or climatic barriers to free intercrossing. Local. Due to the wide distribution of species with inadequate powers of locomotion or migration. Spatial segregation may also be subdivided in con- formity with the causes producing it, thus: 6. Migrational, "caused by powers of locomotion in the organism." 7. Transportational, "caused by activities in the en- vironment that distribute the organism in different dis- tricts." 8. Geological, "caused by geological changes divid- 9 130 CALIFORNIA ACADEMY OP SCIENCES. ing the territory occupied by a species into two or more sections." (d) 9. FertiUzational Segregation. Repugnance of insects to. visiting different plants interchangeably pre- vents hybridization. (e) Artificial Segregation. Artificial selection. B. Eeflexive Segregation. " Segregation arising from the relations in which the members of one species stand to each other." (a) Conjugational Segregation. Due to "the in- stincts by which organisms seek each other and hold together in more or less compact communities." 10. Social. " Produced by the discriminative action of social instincts. The law of social instinct is prefer- ence for that which is familiar in one's companions; and, as in most cases the greatest familiarity is gained with those that are near of kin, it tends to produce breeding within the clan," etc. 11. Sexual. " Produced by the discriminative action of sexual instincts." 12. Germinal. "Caused by the })ropatiation of the species by means of seeds or germs any one of which, when developed, forms a community so related that the members breed with each other more frequently than with the members of other communities." 13. Floral. .Self-fertilization of flowers. (b) linjircgnatiiiiud Segi'i'tjidion. Physiological se- lection ■jtar e.rci'l/c lice . 14. Segregate Siiie. Inability of varieties to inter- breed, owing tu difference in size. 15. Segregate Structure. Due to "lack of correla- tion in the proportionate size of different organs, and l)y other incompatibilities of structure." 16. Potential and Prepoti'ntial. "Caused by more or less free distribution of the fertilizing element to- EVOLUTION OF THE COLORS OP BIRDS. 131 gether with the greater rapidity and power with which the sexual elements of the same species, race, or indi- vidual combine, as contrasted with the rapidity and power with which the elements of different species, races, or individuals combine." 17. Segregate Fecundity. Relation of species or varieties inter se, when free crossing between " members of the same species or variety results in higher fertility than the crossing of dififerent species or varieties." 18. Segregate Vigor. "Relation in which species or varieties stand to each other when the intergenera- tion of members of the same species or variety produces offspring more vigorous than those produced by crossing with other species or varieties." (c) Institutional Segregations. " Produced by the rational purposes of man embodied in institutions that prevent free intergeneration between the different parts of the same race." C. Intensive Segregation. When two or more sections of a species are mutually isolated by any of the above forms of segregation and are subject to the in- fluences of a highly complex transforming agency, there is a reasonable certainty that the different divisions will be differently acted upon. In succeeding generations there will be increasing degrees of divergence and seg- regation, which is termed the law of Intensive Segrega- tion. The different forms of intension are due to difference in food, influence of the environment, use and disuse, correlation of growth, selection, etc. In this case, it will be noticed that Mr. Gulick takes due notice of .the influence of the environment, despite his assertion that variations may, in many instances, be wholly independent of it. It is time to bring this introduction to a close and hasten on to the more special considerations for 132 CALIFORNIA ACADEMY OF SCIENCES. which it is a preparation. The idea which I have attempted to emphasize in the preceding pages is that life has evolved in accordance with tolerably definite and unvarying laws, and that the element of chance, if any such there be, is a very limited one. The living forms of to-day are looked upon as the result of the interplay of organism and environment, progress being urged on by the laws of development and held in check by the laws of heredity; while the organic cosmos is under the ceaseless and untiring scrutiny of natural selection, which, like a wise mother, is perpetually pass- ing judgment on the acts of her children and abmonish- ing them when they go astray. II. The Colors of North American Birds. ON MODES OF PLUMAGE CHANGES. I am not aware of any important addition to the sub- ject of the changes of plumage in birds since William Yarrell, in 1835, published a paper entitled " Observa- tions on the laws which appear to influence the Assump- tion and Changes of Plumage in Birds."* He there distinguished four " modes by which changes in the appearance of the plumage of birds are produced "; (1.) "By the feather itself becoming altered in color." (2.) " By the bird's obtaining a certain number of new feathers without shedding any of the old ones." (3.) " By an entire or partial moulting, at which old feathers are thrown off and new ones produced in their places." (4.) "By the wearing off of the lengthened lighter colored tips of the barbs of the feathers on the body, by which the brighter tints of the plumage underneath are exposed." Trans. Zool. Soc. of London, i, pp. 13-21. EVOLUTION OP THE COLORS OF BIRDS. 133 This first mode of change is doubted even by many- ornithologists of to-day, and yet the testimony presented in Yarrell's paper seems to be conclusive on the point. To be sure, it does seem difficult to understand how a feather, in which there is no circulation, in fact no life, apparently, can alter its color. Mr. Yarrell tried the experiment of marking certain feathers in a bird which he suspected to be changing color, and succeeded in actually observing the addition of pigment. He also says: " On the breasts of several golden Plovers, some of the feathers were entirely white, the colour peculiar to all the feathers of that part of the bird in winter; some were entirely black, being the colour assumed at the breeding season; while others bore almost every possible proportion of well-defined black and white on the same feathers; from which it appears that the same cause of particular colour in new feathers can also partially or entirely change the colour of old ones." Mr. F. 0. Johnson first called my attention to the tails of some Arizona hooded orioles (Icterus cucuUatus nelsoni) in his collection. They represent various stages of transition from yellow to black. I have since examined all the specimens of this bird in the National Museum and the American Museum of Natural History in New York, besides a number in private collections, and from this ample material cannot but conclude that the transition in this species is by an addition of pig- ment without moult. Plate VI shows a tail in a state of change. The primitive color of the tail in this species is yellow, but in the adult male entirely black. The tail figured was of an immature male in changing plumage. The feathers are still yellow for the most part, but one has become almost completely black, only a part of the tip being left yellow. In other feathers little spots of black were visible, while in still others the 134 (.'ALIFORNIA ACADEMY OF SCIENCES. general shade of a part of the feather was dusky, as if only a thin layer of black pigment had been deposited. In other specimens various stages of transition were observable, from the examjile figured to instances where the entire tail was black with simply a few little isolated irregular patches of yellow. Dr. C. Hart Merriam has published an instance of a seasonal change of color occurring by the introduction of pigment without moult, although his views are not accepted by Mr. Ridgway in his Manual. With regard to Allen's ptarmigan (La(jupas Ujgnpus nlleai), the bird in question. Dr. Merriam writes;* "The large series of wings sent by Mr. Comeau demonstrates beyond a question that individual feathers do change color. Most of them are already pure white excepting the shafts of the six outer primaries, which, as usual in winter speci- mens of Ldijoimn ulbuKj are black. The quantity of black varies greatly in the different wings. In those in which the change is most advanced it is merely a nar- row strip of pale sooty-brown, extending along the middle of the upper surfaces of the shafts of the six outer primaries, and is confined to the middle half of the exposed part of each, so that the basal half, and a considerable apical portion, together with all the rest of the wing, is pure white," etc. Mr. Witmer Stone called my attention to specimens of Terps'ijihone crisiatu from Western Africa in the col- lection of the Philadelphia Academy of Sciences, in which an apparent transition of color of the tail without moult is shown, but of an opposite character from the instances above cited, viz.: from dark to light. The tail in the first stage is colored a reddish brown or rufous, this color changing to black, and the black to white, apparently without any moult. In the orioles Ank. ii, pp. --'O'J-iOS. EVOLUTION Of THE COLORS OF BIRDS. 135 this change does not appear to be confined to the tail, but the black patches of the head and throat seem to be developed in the same manner. Thus figure 11 Of Plate I shows a feather from the throat of Icterus cucuUatus nelsoni which is changing from yellow to black. Figure 12 represents a feather from the back of the head of I. buUocki, taken from an immature male of the second year, in which the black was appearing in spots upon a field of yellow. It is impossible to say without more complete investi- gations, and perhaps some experiments upon living birds just how general this change by increase or de- crease of pigment is, but it is probably quite a limited mode of transition. The fourth mode of change, ?'. e., by the wearing off of the dull tip of the feather, leaving the bright under part exposed, is a very common one, among land birds. Dr. Coues has called my attention to a term in the Cen- tury Dictionary covering these two classes of change — aptosochromatism, which is defined as change of color of the plumage without loss or gain of any feathers. He very kindly suggested two new words to indicate these two forms of aptosochromatism; acraptosis, mean- ing the falling off of the tip of the feather, and acropto- sis, implying that the tip is not cast. Plate I shows a number of acraptotic feathers. Figure 6 is a frontal feather of the western yellow-throat {Geothlypis trichas occidentalis) in winter plumage. The basal portion of the feather is much darker than in most feathers, in fact almost black, the median portion a clear ash, and the tip brown. This brown terminal third is inclined to be worn and very brittle. It is so broad that it completely conceals the under portion, but in spring it all crumbles away leaving nothing but the clear ash. Along the line of demarkation of black and ashy the black base is 136 CALIFORNIA ACADEMY OF SCIENCES. sometimes broader and the ashy edging so narrow that the tip wears down to the black. Figure 7 is a feather from the back of the head of the western warbler {Deadroica occidentalis), in winter plumage. In this in- stance the brown edging wears off leaving a yellow feather with a black dot at the tip. In full plumaged birds all this black wears away leaving the head uni- form yellow. Figure 8 is a feather from the breast of the rusty blackbird {Scolecujil/Kiju^'^ caroliaua) , in winter plumage. In the above two instances the brown was so complete as to produce a uniform color, but with the rusty blackbird it is less regular, causing a mottled effect. The brown tip wears off in spring leaving the plumage clear black. Perhaps the two most interesting examples of all, however, are represented in figures 9 and 10 of feathers from the backs of the two species of snow-bunt- ings {PledropJu'wix nivalin and P. hyjierhoreus), nearly in breeding plumage. In P. nivalis (fig. 9), the broad white terminal portion has almost entirely worn away leaving the black base exposed, but it does not wear off thus in P. hyperboreus^ the black remaining white through the breeding season. Mr. Yarrell says: " Young birds of the year in vari- ous species, after the autumn moult, continue through the winter to assume, by degrees, the more intense colours characteristic of adults, without changing the feather. This colour commences generally at that part of the web nearest the body of the bird, and gradually extends outwards till it pervades the whole feather." He calls attention to the influence of the sexual organs in changing plumage. Many birds appear to become more brilliant in color as the breeding season ap- proaches without eitlier a moult or the wearing away of the tips of the feathers (uo'djitosi.'^). This I believe is the case with the house finch {diArj-xjilaciLs -inc.viatiDi.s frontcdis). EVOLUTION OF THE COLORS OF BIRDS. 137 Changes of plumage, then, may be classified as fol- lows: I. Substitution of feathers. 1. By renewal (moult). 2. By addition. II. Modification of feathers (aptosochromatism). 3. By shedding of tip (acraptosis). 4. By change of pigment (acroptosis). _ , -. . \ Different pigment. a. By addition. < ^ .n • ,. ^ intensification of same pigment. b. By loss. The first class, namely, the substitution of feathers, has not been discussed because its bearing upon our subject is less direct, and because it is more familiarly known. It need only be noted here that all birds have an autumn moult, while some have a more or less com- plete spring moult in addition, either in both sexes or in the male only. GENERAL PRINCIPLES OF COLOR IN BIRDS. Having devoted so much space to the fundamental problems underlying all transitions in animals, it will not be possible to consider at any length the general principles of coloration in nature. Indeed, the subject has already been touched upon in discussing sexual selection. However, a few words more are necessary. Colors may be classed, as Poulton has suggested, as structural and pigmental, depending upon the manner in which they are produced. The structural colors are of three sorts — those due to thin plates, one upon an- other; those due to diffraction, where the surface is broken by fine parallel grooves; and those due to re- fraction, where the light passes through a transparent wedge-shaped substance or prism. All of the above 138 CALIFORNIA ACADEMY OF SCIENCES. classes are due to the reflection and interference of light waves, and probably all occur to a greater or less extent among birds, although authorities disagree as to which form is the commonest. The iridescent colors are due to those structural peculiarities. White is due to the presence of minute bubbles of gas contained in the feather which breaks the structure so that the light is refracted in all directions, much on the principle of pulverized glass. The worn, dull plumage of birds, at the close of the breeding season, is due to a similar though coarser form of this same agency. Frequently the outer edge of the wing feathers becomes dull brown- ish, or even nearly white, from becoming worn and abraded, even though its natural color be black.* The vast majority of color effects, particularly among birds, are due to chemical pigments. Many of these piginents have been chemically analyzed and named, and it is found that the same color in different species is not always due to the presence of one pigment, but to different ones. " Thus," says Beddardf " the brown colour of birds is chiefly due not to one pigment, but to two apparently distinct pigments, which give different chemical reactions; to these two pigments their discov- erer, Kriikenberg, has given the name Zoorubin and Pseudozoorubin. An inspection of the feathers would not enable one to tell with certainty which of the two substances was the cause of the colour; but an extract of zoorubin can always be detected by its change to a beau- tiful cherry red on the aildition of the minutest trace of blue sulphate of copper." The theory of bird colors which I shall attempt to elaborate in the succeeding pages is as follows: Pig- * For fuller discussion of structural colors, see Dr. Gaduw, Proc. Zool. Sue, 18S2, p. 409; Poulti.n, Colors of Animiils, pp. 3-11. t Animal Coloration, pp. 2-3. EVOLUTION OF THE COLOES OP BIRDS. 139 ment is a chemical composition thrown off from the system of the bird, probably as a product of waste, and lodged in the integument. The chemical substance thus generated varies in different groups of birds, but is probably generally constant in the species of one genus, or frequently in an entire family. A certain genus would thus be capable of generating only a given num- ber of fundamental colors, but natural and sexual selection by combining and rearranging this limited assortment, can produce a great variety of effects. Be- sides black and white, most North American genera appear to contain but two fundamental colors, but in the tropics, three frequently occur in a single genus. If the pigment be regarded, to some extent at least, as a product of waste due to superabundant vitality, as Wal- lace maintains, it is not difficult to understand how among some tropical birds a, third chemical product might be generated in addition to the usual two. As an illustration of this view, let color be compared to a variety of skin diseases. Each genus of birds in gen- eral, we may say, developes two kinds of skin disease which are bound to be in the system of every species. One of them may sometimes be suppressed or they may be combined in such a way as to be no longer recogniz- able, but they will still be present. This theory could not be demonstrated without further study of the chemical properties of pigment. If it could be shown that in closely allied species the color, although the same, was produced by different pigments; or that in the same or closely allied species, where one color gave the appearance of being a combination of two other colors which occurred in the same or allied species, there was no real connection in the pigments, chemi- cally; the theory would certainly become very weak. Until such experiments have been made, however, it is 140 CALIFORNIA ACADEMY OF SCIENCES. necessary to depend upon appearances, and here there are many facts that seem to support the view. Thus Plates XVIII and XIX seem to be in accordance with it. It will be noticed that in the genus Dendroica olive green is, especially in the female and young, the prevailing color of the group. It is not a little significant that in coloring these two plates it was found that in order to produce this color all that was necessary was to mix black with gamboge yellow, in about equal proportions — black and gamboge being the two most characteristic colors of the specialized males. It might at first sight appear as if this was a modifi- cation from complexity to simplicity, but this is not really the case. If the system of the bird from which the present genus Dendroica was evolved normally pro- duced two pigments which were lodged in the integument, unless some controlling and distributing force were brought to bear upon them, they would naturally be mixed and combined at first, and only after a long pro- cess of selection would the real colors become apparent. This principle may be termed the Law of Assortment of Pigments. If true at all it will be found to have a very wide applicability in the evolution of colors of birds, and, indeed, to underlie all the other principles of color differentiation, although, of course, conditioned by all the more general laws of evolution. The best examples of it are to be found, as might be expected, among the most highly specialized genera, where the colors have changed from some dull hue to distinctly colored patterns. Thus woodpeckers are generally col- ored black and white and scarlet. The combination of the black and scarlet would produce a brown, which is still the body color of some species, as jDrijobnJcs urizoiw. In the genus Tyrannus the original color was probably an olive green, although in many instances where the EVOLUTION OF THE COLORS OP BIRDS. 141 bird is found in arid districts, this color has been bleached out to a brownish or grayish. The more special colors are black and yellow. The male of Pyrocephalus rubineus onexicanus is scarlet and brownish black. The female is colored a plain brown olive, which is a mixture of red and black. The blue jays are generally colored some shade of blue in the adult, together with black and white, but a mixture of these shades would produce the grays of the young and of the less specialized forms as Perisoreus and Picicorvus. The adult male red-winged blackbirds are black and scarlet, the female brown. The meadow lark is brownish or grayish in its generalized color, and black, white and yellow in the specialized shades. I am not certain that the combination of black and yellow (olive-greenish) together with white would produce the grayish-brown of the back, but if this instance be an exception, it is not a very glaring one. The term brown is a very loose one and raay cover a great variety of color effects. It may be produced either by a combination of black and red, or of black and green; or it may be due to the structure of the feather. If a certain amount of gas bubbles are contained in a feather where the pigment is dark, it will produce a brown effect, or a black feather with a frayed edge may appear brown. There is probably no white pigment in birds' feathers, this effect being structural or due to the absence of pigment. Among the orioles, the colors of the specialized males are black and yellow (the orange being merely an inten- sifica.tion of this) while the primitive color as exhibited by the females and young is olive green. Plates XVI and XVII showing the heads of a number of representative species in the generalized and specialized stage illustrates this instance. It might appear that Tdurus spurius with its reddish brown color was an exception to this law, but 142 CALIFORNIA ACADEMY OF SCIENCES. an attempt will be made later to explain this instance in accordance with it. Enough examples have now been given, I trust, to show that, as a rule, the shade of color which we agree to call the primitive color is a composite which, when more or less completely resolved into its component elements, gives the two specialized tints of the species or genus. A word may be said as to the criterion of a general and special color. In the first place, in accord- ance with the law of the correspondence of the onto- genic and phylogenic series, or the tendency of the indi- vidual to repeat ancestral stages, if the young differ from the adult in color (unless the latter be a degenerating form), it will represent an earlier and more generalized type. Furthermore, in an adult male bird the color which is spread over the greater part of the body is ordinarily the generalized color, while the detailed markings represent the more specialized hues. This is directly analogous to the geo,<;'raphical distribution of animals. If we have t'Avo allied species of animals, the one found upon the mainland, the other upon an island, or the one sprcful 0Yt;r a wide urea and the other in a limited section, we should conclude that the species havinij,- a rorifrictcd ranoo had sprung from the species havino- a wide raunc. More espueially would we con- clude thiis if the limited form liad some mark of superi- ority to the other. It is found that among birds the limited markings are, as a rule, of a purer or more sharply (lefin( d color than the body culur. Notice, for instance, the crest of the kinglets or the breast of the rose lireasted gmsbeak. In cases of hit:,h specialization, as with the orioles and tanagers, for instance, the gen- evalized colors may be completely superseded by the specialized, in which case the female and young, alone, would show any trace of them. EVOLUTION OF THE COLORS OF BIRDS. 143 Specialized colors may be classed under four heads, according to the degree of their development: (1) local in the male sex only; (2) local in the species; (3) uni- versal in the male sex only; (4) universal in the spe- cies. As an example of the first may be mentioned the ruby-crowned kinglet {Regulus satrapa olivacea), red- winged blackbird (Agelaius), etc.; of the second, the kingbird {Tyrannus tyrannus); of the third, the scarlet ta,na.gev (Piranga erythroTnelas); and of the fourth, the California woodpecker (Melanerpes formicivorus hairdi). THE PROPORTION AND DISTRIBUTION OF THE COLORS IN NORTH AMERICAN GENERA. It may be well at the outset to take a comprehensive view of the various colors as they appear among North American genera. There are two hundred and nine genera represented among North American birds. Black is present to a greater or less extent in a hundred and thirty-five, and white in a hundred and sixty-nine of thein. Pure red occurs in only thirty-three genera, al- though there are eighty-three besides in which it is present in some such combination as reddish brown, vinaceous, pink, etc., making a total of a hundred and sixteen genera in which some red pigment appears. Pure orange occurs in but ten genera, while yellow is found pure in fifty, and in combinations such as ochra- ceous in twenty-nine others, iiiaking a total of seventy- nine genera in which yellow pigment is found. Green is present in twenty-two genera, but in fourteen of them it is metallic, and hence may not be due to a green pig- ment. Green in combination, particularly with olive, is found in twenty-seven genera, being metallic in only two or three instances. There are accordingly about thirty genera that have green pigment. Blue occurs pure in twenty-three genera, in seven of which it is me- 144 CALIFORNIA ACADEMY OF SCIENCES. tallic or iridescent, while bluish-black or bluish gray is present in thirty-five other genera, giving a total of something like fifty-one genera with blue pigment. Purple is by far the rarest of the colors, only six genera showing it pure and seven in combination, while out of these thirteen instances it is iridescent in ten. Gray and brown are the most difficult colors to assign to a given nunaber of genera, because they frequently occur only in the young, while in a large number of instances the two hues are more or less combined. In general, however, it may be said that gray occurs pure in a hun- dred and thirteen genera, and in combination in thirty- nine others, making a total of a hundred and fifty-two. Brown is found pure in a hundred and twenty-nine in- stances, while in combination it exists in forty-three additional genera, — a hundred and seventy-two in all. These somewhat dry statistics of the relative abundance of the different colors may be shown more clearly in the following condensed table: Total number of genera . .... . 209 Yellow . . 79 Blue 51 Green 30 Orange .10 Purple . . 3 The above facts are susceptible of more than one in- terpretation. The very large number of genera in which brown is present may be accounted for by the fact that brown affords better protection, and that where it ap- pears it is a protective color which has been developed by natural selection. The same argument might be ap- plied to gray, while black and white usually occur in such limited areas that they may be looked upon simply as recognition markings. There is, however, another Brown .172 White... ..169 Gray .. . 152 Black . . . .135 Red . .116 EVOLUTION OP THE COLORS OP BIRDS. 145 view which seems to be more in harmony with the facts. Brown and gray are generally present in species in which the markings are not highly specialized. More- over, these colors very frequently occur in the young of species which are highly specialized in the adult, as, for example, in the red-headed woodpecker [MeLanerptfs erythrocephalus). The presence of brown or gray in al- most every genus of North American birds, either in the young or the adult stage, would seem to indicate that these are the most primitive colors, and that where they still occur it is due to a lack of specialization in this respect. To be sure, in many cases this specialization may be retarded in many instances by the positive ad- vantage of protection, or protection on the contrary may enable it to continue. As an excellent example of these two cases maybe mentioned the goldfinches. The pine finch {Spinus pinus), retains the primitive plum- age, perhaps from the need of protection, while the gold- finches (Spinus tristis for example), have become special- ized in color without sacrificing protection. They frequent during the summer the yellow compositee, in the vicinity of which they can be detected only with great difficulty. This view would be in harmony with the law of assort- ment of pigments. The tendency would be to progress from such mixed shades as brown and gray to the pure colors. The need of recognition would in any event be sufficient to account for the early and universal tend- ency to produce limited areas of black and white. It might at first sight appear as if the fact that green is less frequently found than either of its constituent ele- ments, yellow and blue, would militate against the law of the assortment of pigments. This discrepancy is only an apparent one, however. The green pigment of the bird is a different chemical substance from either the 10 146 CALIFORNIA ACADEMY OF SCIENCES. yellow or the blue. It might be that in certain in- stances, especially among tropical birds, that a green color was produced simply by a combination of yellow and blue pigments, in which case we shall have the primitive color of the bird, as indicated either by the young stage, or by the body color of the adult, green, and the special- ized colors, yellow and blue. In general, however, the green is probably either a different pigment, or, as is frequently the case, in olive greens, produced by a com- bination of yellow and black. It may be well to consider next each of the primary colors (together with black and white) more particularly. More species are wholly or largely black than any other of the primary shades. The following are exclusively or almost completely black: Catharista atrata. Scolecophagus. Orotophaga ani. Quiscalus. Crotophaga sulciroatris. Progne subis. Corvus. Phainopepla nitens. Molothrus ceneus. Still larger is the list of species in which black covers a large proportion but not the entire surface of the body: Colinus virginianus cuban- Pica pica hudsonica. ensis. Dolichonyx orysivorus. Pseuclogryjjhus californianus. Molothrus ater. Cathartes aura. Agelaius. Urubitinga anihrctcina. Spinus psaltria mexicana. Campephilus p)rincipalis. Sprophila 'morelletti. Xenopicus albolarvatus. Euetheia bicolor. Sphyrapicus thyroideus. Calamospiza melanocorys. A number of species are colored a very dark brown or gray, showing a strong tendency towards black. The list of these is as follows: EVOLUTION OP THE COLORS OF BIRDS. 147 Parabuteo unicinctus liar- Arclnbuteo lagopus sancti- risi. joltunnis. Buteo harlani. Geophloeus pileatus. Buteo abbreviatus. Leucosticte airata. Buteo sivainsoni. Junco hyemcdis. Buteo fuliginosus. Sayornis nigricans. Falco columbarius sucldeyi. There are thus something like forty-five or fifty North American species which show a very strong tendency toward melanism. The relation of geographical distri- bution to this subject will be discussed at a later stage of our inquiry. Besides these species in which black is the sole or predominant hue, there are a number in which it figures quite largely. Thus the genus Pipilo contains two groups, erythro23hthalmufi and maculatus in which the back, throat and breast are mainly black. The American redstart Setophaga riUicella has the black distributed in precisely the same manner, while in the painted redstart (S. picta) there is a still greater pre- dominance of black. Indeed, there is a curious paral- lelism between the colors in these two widely separated genera which may be only a coincidence or may be a matter of profound significance. At any rate it is a subject of great importance in an investigation like the present, to scrutinize all these apparent coincidences and see if they may not have some real meaning. In the first place, then, Pipilo erythrophthalmus and Setophaga ruticilla both have the black of the male distributed over the same parts of the body. There is the same abrupt contrast between the black of the breast and the white of the belly. The sides of the breast are red in both species, although in the one it is a bright fiame reddish-orange (Setophaga) while in the other it is chest- nut or rufous. There is a light patch on the wing, orange in Setophaga and white in Pipilo. The tail 148 CALIFORNIA ACADEMY OP SCIENCES. markings are decidedly different, however, being basal in Setophaga and terminal in Pipilo. In both species the black of the male is replaced in the female by brown. Perhaps the most curious point of resemblance, how- ever, is the fact that both species which belong to the eastern states, have western or southwestern represent- atives (Setoph.aga picta and Pipilo maculatus) in which there is a greater amount of black, and in which the sexes are colored alike. To be sure, the difference in structure, size and general appearance between these two birds is so great as to apparently preclude any possi- bility of kinship, yet the parallelism is complete in so many points that it is difficult to believe it to be a mere coincidence. There are, however, several species in which the color of the back, head, throat and breast is black or some very dark shade, in abrupt contrast to the pure white of the breast. Such, for instance, is the case with Junco hyemalis and Sayornis nigrescens. Again, the area of black may be the same, but the un- der parts some color, such as yellow or brown, instead of white. As examples of this Icterus parisorum and I. spurius may be cited. The general style of coloration in the rose-breasted grosbeak f if aftia ludovicianaj is the same, although the black is interrupted on the back by a patch of rose color. This species forms a connect- ing stage between such forms as Pipilo, Setophaga, Junco and Sayornis, where the black extends from the back around the throat and breast, and such forms as the Blackburnian warbler (Bendroica blackburnice), where the entire upper parts are black and the entire lower parts light colored. In the magnolia warbler (B. maculosa), the black is still an important feature of the back, but less evenly distributed, not covering the top of the head, and frequently broken by olive green. It also appears in decided streakings upon the breast and sides. EVOLUTION OF THE COLORS OP BIRDS. 149 In general, it may be said that the tendency is for the darlc markings, whetlier black or some other shade, to occur in the greatest masses upon the back. As will be seen later, this might be accounted for by supposing that light is inclined to favor the deposit of pigment, and as the back has always received a more considerable share of it than the breast, a rhythm had in the course of ages been established, inclining the larger amount of pigment to those parts of the body. As if to bid defiance to any such laws as we may make upon the subject, a irumber of species are found in which this order is directly reversed. Thus, in the chestnut-colored long- spur fCulcarius ornatus) the top of the head and entire lower parts, except throat are black. The same parts are colored black in the grassquit (Eiietlieia bicolor) and in the bobolink (Dolichonyx oryzivovus). In all these cases the upper parts contain the lighter markings. These black markings seem as a rule to spread from certain well marked areas. Those on the lower parts appear to spread from the throat or breast patch, while those of the upper parts usually come first on the head. This is by no means universally the case, as, for in- stance, with the genus Icterus (Plates XVI-XVII). In the females the only patch of black is the one on the throat. It does not extend from there at first, however, but the back darkens, as in the adult of Icterus cucuUaius. In Icterus bullocki the black has extended over the head, while in the next stage, Icterus galbula, the patches on throat and back of head become confluent. The point to be noted is that there is no species in which the top of the head is black while the back remains light colored. Sometimes when the entire bird is black or some dark shade, its antecedent stage is black above and light below. A good example of this is the purple martin (Progne subis), the male being entirely dark glossy blue 150 CALIFORNIA ACADEMY OF SCIENCES. black, while the female has the under parts gray and white. Among the blackbirds, the females frequently have the under parts lighter than the back. This is noticeable in Scolecophagus and extremely pronounced in Agelaius. In Xanthocephalus, the breast of the female is mixed with white. In the hawks it is fre- quently the case that a melanistic phase will occur in which the bird is dark above and below, whereas, in the normal phase the breast is light colored. Such is the case, for example, with Bideo horealis and B. sicuinsoni. Some of the tanagers (Plranga erythromclas, for in- stance), present a rather unusual localization of black, the wings and tail alone being shaded thus. In the Louisiana tanager ('Pivfinrja ludovicianaj the back as well as the wings and tail is black. P. erythromehis un- doubtedly represents a more advanced stage, in which the black has become restricted to these regions. Perhaps the most instructive example of the way the black spreads from the breast, as a center of pigmenta- tion, is the female of Williamson's sapsucker 6Sy;/;?,/)'((_/)(;- cd.s thyroideusj. The final color of the male is an almost uniform black, varied on the breast by only one patch of red on the throat. Every stage may be traced from the young female Avith white under parts, through the adult female with a black patch upon the breast, and the different stages of its extension in the young males to the final plumage of the adult. The most complete example with which I am ac- quainted of the spreading of black upon the back is the green-backed goldfinch and its allies (Plate A'll). Spinu-^ pn(dtr'iccome still more elongated, and spread not only to the shaft, but across it on the outer edge. In the fourth and fifth primaries the white continues to spread until it occupies almost the entire basal half of the feather. A little dark pigment at the extreme base of the fifth feather asserts itself in the sixth, forming a well marked patch of brown. This spreads down the shaft in the seventh feather, and in the eighth has iso- lated the white in two patches, a long one along the inner edge of the feather and a shorter one midway EVOLUTION OF THE COLORS OF BIRDS. 169 along the outer edge. In the ninth primarjr this outer white patch has vanished, the one on the inner edge persisting in a long line on the edge of all the second- aries. The first secondary is well marked off from the last primary by a spot of white at the terminal end of the white border. A second spot is gradually constricted off from the end of the border, and the first one dwindles into insignificance. It is time now to ask the meaning of this successional taxology in the color pattern. If the successional tax- ology represents different evolutionary stages of pro- gression, as I believe it does in some cases, it is easily understood. For example, in the feathers of Melanerpes, previously described, it is only necessary to assume that the under part of the body is becoming black, but the tendency has been stronger on the upper part of the breast than lower down, to understand this successional relation perfectly, as different degrees of complete- ness in evolution in different parts of tlie body. This is a beautiful example of Cope's law of acceleration and retardation. The growth force has been accelerated on the upper breast and retarded on the belly. With re- gard to wing feathers, however, the explanation is not so simple. Here, instead of one part of the body ex- hibiting a general stage of development, and other parts successively higher stages, we find feather following feather in uniform steps of transition, when in many cases it is simply impossible to say that one stage is higher than another. Certainly there is not an ideal mode of coloration being approached through successive stages, as is the case with feathers becoming black, but rather a variety of individual patterns combined to produce one effect. Thus far little has been said of general effects. The question has been discussed as if it were supposed that 170 CALIFORNIA ACADEMY OF SCIENCES. all colors were produced strictly in accordance with these laws and utterly regardless of any external in- fluences which might modify the patterns. We must, however, frankly acknowledge that, while all internal and constitutional laws of development must rigidly limit and condition the assumption of pigment by a feather, a large proportion of color markings are produced by ex- ternal causes — natural and sexual selection, direct action of the environment, etc. For example, the general laws of the location of growth force might have caused the pigment to have lodged in the tips of the feathers of the thrush's breast, but the effect would have been one of mottling. Then natural selection might have taken advantage of this and emphasized and defined the mark- ings, and left each one distinct and isolated as a spot. And thus it is with the wing bars and bands under con- sideration. They have doubtless been produced by selection for some effect, and indeed it might be argued that the orderly sequence from feather to feather was due solely to the fact that in this manner the general effect might best be secured. This view, however, can, I think, easily be shown to be untenable. For example, upon the last primary of a wing of the Californian wood- pecker (ilfelaiicrpes fcn'inicivorus huinJi), which I ex- amined, was a mere suggestion of a white dot below the strip of white on the inner side of the feather. It Avas so snrall that it might easily have been overlooked in an examination of the feather, and most certainly could have had no more influence on the general appearance of the feather than a speck of dust. Upon the feather next it, the first secondary, a well marked spot appears in exactly the same place, while in the secondaries suc- cessively following, the first this spot slowly dwindles away. Now it might of course be argued that this spot had Ijcen a useful character at some past time, but was EVOLUTION OF THE COLORS OF BIEDS. 171 becoming obliterated. This objection wholly misses the point, however, which is, not why does this little dot which can be of no utility exist but why does it occur as anticipating a larger spot? This is only one instance out of an innumerable number of cases where a well marked character in one feather is led up to by anticipatory stages. I would suggest that the term Repetitive Marks be used to designate these characters. These rep- etitive marks, from their very nature, cannot be useful characters nor can they be rudimentary. The most probable explanation of them appears to be that they have been developed in accordance with the law of repe- tition. This is a form of correlative development, but it does not appear by any means adequate to completely explain the case. In a general way it might be under- stood that if a definite manifestation of growth force were located in one feather, there would a tendency to repeat this less and less completely in succeeding feath- ers. It might seem, however, that this repetition pre- cedes and leads up to the complete form rather than fol- lows it. Of course it is difficult to say which end is the beginning of the series, but it might seem at first glance as if it should begin with the first primaries and end with the tertiaries, these latter being less specialized. In reality, however, it seems more rational to suppose that the tendency works from the simple to the complex. Going from the secondaries toward the primaries it is found that while certain characters are becoming more developed others are fading out. Thus in wing of the sparrow-hawk (Plate III), proceeding from the tertiaries towards the primaries the black bars are found to be progressing in complexity, while at the same time the black subterminal spot of fig. 39 diminishes and lingers on as a repetitive spot to fig. 30. All that can be said of this successional taxology in marks as exhibited on 172 CALIFORNIA ACADEMY OF SCIENCES. tlie wing feathers is that it is not due to selection or any external force, but rather to some unknown principle of repetition or correlation. Thus far the discussion has been confined to black and white, or brown and white markings. As soon as colored feathers are brought into consideration the factor of selection immediately becomes more prominent. It is a noteworthy fact that along the line of division of (wo patches of color the feathers are not uniformly colored, some the one shade and others the other, on the contrary the two colors in a large number of cases appear on the same feather. It will be found con- venient to designate these as Hybrid Feathers. Take for instance the rose-breasted grosbeak where the black, white and rose color come together on the breast and sides of the head. Some of the feathers are colored black and white, the shaft dividing the two, and each color contiguous to the general patch of that color. Others are colored rose and white, the rose generally at the base of the feather and adjacent to the rose patch, the white at the tip of the feather and helping to cut the white line of the breast from the rose of the throat. Many rose and black feathers are to be found, the shaft generally dividing the two colors, although sometimes there is merely a black spot at the tip. The point to be noticed is that the colors are not as a rule distributed in accordance with any law of growth force, but in any way which will produce the general effect of a rose coloi'ed patch with moderately sharply marked limita- tions, bordered with black on the sides and white below. l)ccasionally a very interesting feather is found which lieautifuUy illustrates the interplay of internal and ex- ternal effects. Such a one, for instance, was marked according to the ideal mode of pigment deposition with a dark tip and border, but only on the side nearest the EVOLUTION OF THE COLORS OF BIRDS. 173 black patch, the pigment having been directed to that side of the shaft by natural selection but still insisting upon following the conventional route of travel. The Californian woodpecker (Melanerpes formicivorus haivdl) affords several especially fine illustrations of color for effect regardless of the laws of growth. Thus at the line of demarcation of the white of the frons and the scarlet of the occiput, which is quite clearly cut, nearly all the feathers are literally cut in two by the color, the basal half being white and the distal end scarlet. Along the sides of the head many of the feathers are scarlet terminally and black basally, but" I fail to discover any feathers at the base of the scarlet patch which are black terminally. Here again we have an illustration of how natural selection must still be limited. The scarlet was able to come in upon the white pigmentless feathers or the white to encroach upon the scarlet, but the black did not seem able to get a foothold upon the tips of the scarlet feathers in a corresponding manner. The throat markings are interesting as being remark- ably free from hybrid feathers. This is particularly the case with the feathers of the black jugular patch where it meets the yellowish crescent of the throat, hybrids being almost wholly absent here. They also play a very subordinate role at the lower end of the throat crescent where it joins the black of the breast, although some of the feathers here have a narrow edging of black. The red-shafted flicker {Golaptes cafer) presents some interest- ing features with regard to hybrid feathers. The red malar streaks, or moustaches, occupy a tolerably dis- tinct pterylographical area, and are well separated from the feathers of the throat by a bare tract. Accordingly hybrid feathers are almost or wholly wanting on the in- side edge and rare on the outside of the streak. The black crescent on the breast is of especial interest be- 174 CALIFORNIA ACADEMY OF SCIENCES. cause strongly marked hybrid feathers form both the upper and the lower line of the patch. The upper line is formed by white feathers with the distal half sharply black, and the lower edge by black feathers with the distal end edged with white. This is rather unusual, for the rule is that when the base and tip of a feather are differently colored on one side of a patch they pre- serve the same relative positions upon the other side. In order to study these hybrid feathers more system- atically I shall make the following classification: I. Hybrids (feathers of two or more colors helping to define a patch). 1. Symmetrical. a. Lateral. , ~ f Relative iiositions uniform. b. Transverse <^ r. i ,- •^- • ^ i ui L Kelative position msterchangeable 2. A.symmetrical. a. Sharply marked. b. Indistinctly defined. II. Pseudohybrids (feathers of two or more colors not helping to define a patch). 1. Sharpl}'^ marked. a. Both colors showing. b. Only one color showing, the other concealed. 2. Tinged with some foreign color. I will now explain each of these divisions and give examples. I have restricted the term hybrid feathers to such as are divided into two or more parts by color and in which each color shows in the general pattern of the bird. Where two colors show in a feather but have no significance in defining a patch, I have termed them pseudohybrids. In a large proportion of cases patches of color are marked on one side at least by true hybrid feathers. When the feathers are divided into two toler- ably uniform parts they may be considered as sym- EVOLUTION OF THE COLORS OV BIRDS. 175 metrical. Then the question is are the divisions lateral or transverse? This is determined in the main by the position of the patch. If the feathers in question occur on the side of a patch they are ordinarily divided later- ally. Thus the white streak down the back of the downy woodpecker {Bryobates pubescens) is defined along its sides by feathers which are, in general, white on the inner side of the shaft and black on the outer. So also with the streaks on the head of the meadow lark {Stu7'- nella magna), the boundaries of which are fixed by feathers which are white on one side and brown on the other. Examples of tranverse symmetrical hybrids have already been given, no better case being known than such as the dividing line between the white and red across the head of the Californian woodpecker (ilfeZccnfirpes jormicivoruH hairdi). When a band occurs, as for instance, across the head or breast, cutting some uniform ground color into two areas, the line of demarcation is generally made by hybrid feathers on one side only. Thus the breast of the belted kingfisher (Geryie, alcyon) is white, but crossed by a broad, well-defined band of blue. The white feath- ers along the upper border of this blue strip are edged with blue, and both the blue and white in a single feather are visible. Accordingly the line separating the white from the blue along this edge is not made by the tips of feathers of one color overlapping another, but cuts right through the center of the visible part of the feather. The blue feathers along the lower edge of the blue patch, on the contrary, were not, in the specimens examined, edged with white. In other words, the lower border of the blue patch is marked off simply by the tips of the blue feathers overlapping the white feathers. This state of affairs is due to the fact that in all the feathers of the breast the relative position of the colors 176 CALIFORNIA ACADEMY OF SCIKNCES. is constant, that is, if there be two colors, the white will occupy the base of the feather and the blue the tip. This is probably due to the fact that the breast of this species Avas white, and that the blue pigment which came into these white feathers, in following out a gen- eral law of pigment distribution, sought the tip of the feather in every case. Or the converse may be true, that the breast was blue, and that in becoming white the base of the feather was uniformly affected first. The black crescent on the breast of the red-shafted flicker (ColapUN cufev) has already been mentioned as a case where the relative position of the colors on the hybrid feathers is interchangeable. In other words, both the upper and the lower border of the black patch is defined by hybrid feathers — the upper border by light feathers with black edgings, the lower border by black feathers with light edgings. We come next to the asymmetrical hybrids. It would be wrong to suppose that there is a sharp distinction between these two classes. Hybrids which are not asymmetrical are really quite the excep- tion. The distinction is made to express the difference between hybrids where a definite plan is followed to produce the effect, as by the cutting of the feather in two, more or less regularly either transversely or lateral- ly, and hybrids where no regularity is observed, but the two colors distributed on the feather more or less at random. Many of the hybrid feathers on the throat of the rose-breasted grosbeak (Habia ludoviciana) are of this asymmetrical type. So also are they on the back of the neck of the golden-crowned sparrow (Zonotrichia coro- nata) where the black, white and brown are all mingled, but the area of each color sharply defined. Asymmetrical hybrids are sometimes not sharply de- fined as in the preceding instances, but the two colors EVOLUTION OF THE COLORS OF BIRDS. 177 blend more or less at the point of meeting. This is the case in the vermilion flycatcher {Pyrocephalus rubhieus mexicanus) , where the scarlet feathers along the border of the crown are brown, basally, but the two colors are not sharply separated on the feather. This is also the case with the white and slate-colored hybrids of Jv.nco hyemalis. Besides these hybrid feathers, which help to define patches of color on the bird, there are other feathers which are of two or more colors, but which are of no apparent utilitarian significance. These I have called pseudohybrids. They are especially interesting as showing the sort of material furnished to natural selection with which to produce effects. It is evi- dent that along the line of demarcation of two colors the pigments are apt to get confused as to which is their proper route, and hence both come upon the same feather, by accident, as it were. Natural selection has frequently used this chance commingling for the production of effects, but has not always done so. Thus true hybrids are almost wanting in the crown patches of th« goldfinches, but pseudohybrids are not uncommon. They are feathers in which the black of the crown and the olive of the back are both present, but instead of helping to define the black patch they rather tend to break up the symmetry of its bound- ary. This is especially noticeable in specimens of Spinus psaltria and S.la^vrencei. In the latter the feath- ers along the edge of the crown patch are pseudohybrids, and the same is true of those between the yellow and gray of the breast. Another class of sharply marked pseudohybrids are those in which one color is completely concealed by overlapping feathers. Such pseudohybrids are very common and are interesting as being in most instances 12 17s CALIFORNIA ACADEMY OF SCIENCES. apparently vestiges of some former color of the bird. This under color is of no more utility than a rudimen- tary organ. A good illustration of this class is presented by the feathers of the black throat patch of the meadow lark {Sturnella xicujnit). These feathers generally have a white basal portion and a black terminal portion, with a more or less decided tinge of yellow upon the white nearest the edge of the black. This is plainly a relic of the time when the breast was all yellow, for only the black is now visible, and the white and yellow bases could be of no possible utility. These feathers are very common in patches of bright color, as the scarlet head of the Californian woodpecker, where the feathers are black below the scarlet. It is interesting to note that the extent and distinctness of the subterminal line line of black on the scarlet feathers decreases in orderly succession from the feathers of the frons backward toward those of the nape. This is directly parallel with the extent of the scarlet on the head of the different forms now living. The scarlet in these decreases and the black increases from the frons backward. In gen- eral, it may be said that true hybrids occur only along the border line of two color areas, while pseudohybrids are sometimes the only form found throughout an entire color patch. There is but one other form of psevidohybrid to be considered and this an uncommon variety. In the red- winged black birds the line of division of white and scarlet upon the shoulder is made by the scarlet feathers overlapping the white. In other words, there are no true hybrids. Frequently in Agelalns tricolor an infu- sion of pink or bufiy is noticed upon the white feathers as if some of the scarlet pigment had run in upon the white by mistake. A. gubernator frequently has a blush of scarlet upon the buffy feathers. EVOLUTION OV THE COLORS OF BIRDS. 179 We come next to the general patterns of bird colors. These are so infinitely varied and complex that it will be almost impossible to bring them under any universal law or laws, but at least a few generalizations must be made. Eimer has stated* " that the appearance of new characters always takes place at definite parts of the body, usually the posterior end, and during develop- ment — with age — passes forwards, while still newer characters follow after from behin.d. Thus during life, e. g. in lizards, a series of markings pass in succession over the body from behind forwards, just as one wave follows another, and the anterior ones vanish while new ones appear behind." This development from posterior to anterior is illustrated by many examples among birds, but seems to me to have far too many exceptions to be held as as a general law of development. The succes- sional taxology of markings on the under parts of many of the hawks, conforms to this rule. Upon the breast the markings are simple streaks, but from this stage they pass into spots and from spots into bars which are most distinctly marked upon the lower part of the flanks and belly. This is especially well shown in the western red-tailed hawk {Buteo borealis calurus). It is also well illustrated by a large number of the wood- peckers, especially in the genera Dryobates and Picoides which have the flanks barred and the breast streaked or plain. The reverse is true with the Californian wood- pecker, where, as we have already seen, the markings simplify instead of specialize as we approach the abdo- men (see ante p. 163 and Plate II, figs. 1-6). So also in the lark bunting {Calamospisa melanocorys), the specializ- ation begins at the anterior end. In immature males the throat first becomes black, and in a series of males it is found that the tendency is for it to spread from this *' Organic Evolution, p. 28. 180 CALIFORNIA ACADEMY OF SCIENCES. point downward to the tail in tolerably uniform succes- sion. The Louisiana tanager {Pirwuga ludoviciana), is doubtless colored somewhat after the fashion of the primitive color of the scarlet tanager (P. erythromelas) , which had a yellow ancestor; and here the specialized color, the scarlet, first asserts itself upon the anterior part of the head and throat, spreading thence down the back and breast, to a greater or less degree depending upon the perfection of plumage of the bird. Many of the conclusions concerning the feather patterns will apply also to the pattern of the bird as a whole. Thus, just as the streaked feather is the most primitive so also is the streaked plumage. This is exemplified by the young of a large number of birds. Thus the breast in many of the sparrows, such as Zono- trichia,Chondestes, Spizella, Junco, Amphispiza,Peuc£ea, and Pipilo, which is pure white or buffy in the adult is streaked in the young, and in many instances the back also is streaked. The ])h\e siskin {Sj)i'iius pinus), seems to have preserved this primitive plumage with very little variation, in its adult state. Again, just as the accumu- lation of pigment at the point or on the edge of the feather is an early stage, so do we find many young birds with a mottled plumage such as would be produced in this manner. Looking at birds broadly, the endless modification of pattern and infinite variety in the form and position of color areas is simply bewildering. Out of this chaos, however, it is possible to bring some semblance of order by showing what forms of marking never or seldom occur and what forms are most often repeated. In the first place there are no birds marked with an asymmetrical pattern. It seems hardly fair to explain this fact wholly by the law of bilateral symmetry, for this law does not apply in the least to individual EVOLUTION OF THE COLORS OP BIRDS. 181 feathers. Still there is probably a general tendency to repeat the same pattern on both sides of the body, just as there seems to be a tendency to repeat a general style of marking on the lower that has been produced on the upper part of the body. The asymmetry of hybrid flickers is an abnormal case, and would hence not be an exception to the rule of bilateral symmetry, which is intended only for normal forms. Although a streak may occur either just over or through the eye, I know of no instance where a streak runs near or through the eye at right angles to the su- perciliary stripe. I know of no species which has either the throat or the top of the head barred, nor can I think of any instance where any definite pattern of color occurs on the back proper. Neither does any instance come to me where a single streak down the middle of the back (as in Dryohates pubescens) is continued without interruption over the top of the head to the bill, nor where a similar streak on the, under parts, extending down the throat and median breast, (as the carmine of Pyrrhuloxia sinuata) extends also down on the abdomen and under tail coverts. I can think of no species in which a single transverse band or bar crosses the back below the nape (where it occurs in Bolichonyx oryzivorus, for example), nor of any instance where such a band or bar crosses the under parts of the body below the breast. No instance is recalled where large spots of any kind occur either on the throat or head. It may seem like an idle task to enumerate these forms of marking which do not occur, but by next noting what styles are most common, the two will be brought out in strong relief. The head is by far the most complexly marked part of the body. Of the head markings the superciliary stripe is the most universal, being char- acteristic not merely of birds but also of many reptiles 182 CALIFORNIA ACADEMY OF SCIENCES. and mammals. Next most common is the throat j^atch which is not strictly but mainly confined to the ptery- lograpliical region lying between the lower jaw bones and extending downward along that line. A transverse stripe on the frons either of light or dark is very com- mon, as in Melanerpes formicivorus bairdi, Geothlypis trichas, Dendroica dominica, etc. So also a transverse band on the nape is common as in Cyanocitta cristata, DoUchonijx oryzimrufi. A median line on the head is com- mon, as in Sturnella magna, Reguhis mtrapa, Tyrannusi tyrannies, the young of Habia, and many others. A con- trasted transverse band terminating the throat patch is common, as in Hesperocichla na-viu, (Jyunocitti/ cristata, etc. In fact, whenever the breast has any diversity of marking a breast patch of some sort is the general rule. The belly is only A-ery exceptionally marked, and then either simply streaked or barred, or more rarely, spotted as in Colaptes, but the flanks are usually marked either a darker shade than the belly or streaked or barred. The under tail coverts are frequently streaked, barred, or colored quite differently from the belly as in the cat bird {G(d.eoscoptes carolinensis) and Californian towhee {Pipilo fuscus criHS(dis). The rump patch is very often marked by some conspicuous color as in the yellow- rumped warbler {Dendroica coronata) and the flicker {Colaptes aundux). The wing and tail markings are strikingly varied and characteristic of species. In accounting for these patches of color and their distribution in diverse patterns it will be necessary, it seems to me, to abandon wholly or largely internal laws of growth as explanation. Dr. Harrison Allen has pub- lished a paper on the Distribution of Color Marks of the Mammalia* in which he elaborates the view that the distribution of pigment is favored by the presence of * Proc. Acad. Nat. Sci. Phil., 18S8. EVOLUTION OF THE COLORS OF BIRDS. 183 large masses of muscle lying beneath the surface or by nerve terminals, which produce great local activity and excess of nourishment in particular parts of the body. Inasmuch as the large masses of muscle and important nerve terminals are more or less constant, especially among species of the same genus, whereas the areas of color may be profoundly different, it does not seem possible that this factor can be a very strong one, if operative at all among birds. The frequent occurrence of a patch of color on the breast where the largest muscles of the body are situated, might be, to some ex- tent, due to this influence however. With regard to the great frequency of a strongly marked throat patch Dr. Stejneger suggested to me the possibility that the con- stant vibration of the throat in singing might be a factor in the specialization of its color. There could not be any direct connection between the motion of the throat and singing, however, because sometimes the patch is distinguished by the presence of pigment as in Harris's sparrow {Zonotrichiu querula) which has a black throat, while in the same genus even, a species occurs in which the throat is marked off by the absence of pigment — the white-throated sparrow {Zonotrichiu alhicollis). More- over, the canary, which shakes its throat as if it would burst, has not produced any perceptible difference in this region, nor has the mocking bird {Mimus polyglottos) in which the throat and breast are uniform white. Dr. Stejneger's theory has suggested to me another view which is not open to these objections. The frequent vibration of the throat, especially during the courting season, would make it almost the most conspicuous part of the body, and it seems highlj^ probable that when- ever any suggestion of pigment occurred there it would be retained and encouraged by sexual selection. It might also prove a useful recognition mark in many instances. 184 CALIFORNIA ACADEMY OF .SCIENCES. According to this same priiicijile of the coii.spicuou.s- iiess of moving parts, other markings may possibly be expLiined. A considerable number of birds have the edge of the wing along the shoulder, decidedly marked with yellow, white, rose, etc. It is especially on the under side of the wing and not very readily seen when the bird is at rest. During the courting season the males of many species have a habit of rapidly vibrating their wings m a slightly lowered position. I have noticed this among the sparrows such as Gambel's sparrow {Zonofrichin leiicophrys (jdinhe.li), and I think the western savanna sparrow {A])i'iaodr(titi,u>< saadwichensis alundi- iiufi). It is probable that this habit obtains with the grasshopper sparrow {A. fiuvunnarinii jxisserlnufi) in which the wing is so conspicuously edged with yellow, and has been developed by selection in the same man- ner as the throat patch. Frequently the under wing coverts are colored peculiarly and sometimes very beau- tifully, as in the rose-breasted grosbeak. When the male bird is paying his addresses to the female this patch would be sometimes obscured and sometimes visi- ble, and accordingly more conspicuous and beautiful than if always in plain sight. Audubon, in his plate of this species, represents a male facing a female with wings raised to show this patch, but it may lie that he drew it thus in order that the spectator might see the marking, and not because he had ever seen the birds in that attitude. The rump is very frequently colored dif- ferently from the back and tail (as in JJcndivica coronato), or when colored the same is more intense (as in Hitrjxi- iliivns rncxicumis frontcdis). When courting, the wings and tail are lowered and the rump accordingly is very (■onspicuous. The under tail coverts are frequently col- ored differently from the belly or tail, and generally in species which live amongst the underbrush dodging EVOLUTION OP THE COLORS OF BIRDS. 185 about with the tail frequently thrown up in the air. This patch of color would accordingly be of great use as a recognition marking — but this subject will be more fully discussed later. It thus seems that the markings of the throat, under tail coverts, rump and under wing may be explained by selection. These markings are determined in their shape chiefly, if not entirely, by the part affected, and hence present no particular difficulties. With the head markings the problem is, however, not so simple. We have already seen that lateral markings are common upon the head while transverse markings occur only in special parts and there less frequently than the others. The superciliary stripe is much the commonest of marks, and being generally white in color, there seems far more probability that it is due to some internal principle than is the case with any other bird marking. The fact that frequently where no superciliary stripe occurs in the male it is present in the female or young would also seem to indicate that it is constitutional rather than utilitarian in nature. Instances of this sort are the bay- breasted warbler {Denclroica castanea), red-winged black- bird {Agelaius phceniceus), bobolink {Bolichonyx orijzi- rorus), etc. There are at least a hundred and six North American land birds in which the white superciliary stripe occurs, from the bob white (Golinus virginianus) at one end of the list, to the wood thrush {Turdus inus- telinus) at the other. In the genus Dendroica it is especially prominent, being present in eleven species and generally very sharply defined. It is also present in nine species of the genus Vireo, and among a large number of warblers of other genera than Dendroica, as well as many of the Fringillidse. It is not always, although generally, a narrow sharply defined line.- In the western night hawk ( C/iorcfez7es virginianus henriji), for instance. 186 CALIFORNIA ACADEMY OF SCIENCES. its boundary is not sharply defined, while in the chuck- will's-widow {Ant7'08tomu'i carolinensis) it is a very broad band. In the California jay {Aphdocoina. calif ornica) it is sharply defined but is composed of a series of fine white streaks or spots, and hence is not a continuous line. It hardly seems within the bounds of reason to suppose that all the species which exhibit this mark are the descendants of a common ancestor which pos- sessed it, and that it has persisted without significance for so long a time, although this would not perhaps be any less conceivable than the retention by man of the pineal eye. On the other hand, it can hardly be held that the superciliary stripe is a recognition mark, be- cause it is very often inconspicuous in life, although sometimes very noticeable, as in the varied thrush {Heaper- ocichlu ■ncvvi((), where it forms one of the very best char- acters for recognizing the bird instantly, even though at a distance. Among many of the warblers, vireos and sparrows, where it is present in closely allied species, it would not serve, however, as a help in detecting the species. There is one thing which seems to be of some sig- nificance — that this marking so universally present in the most diverse groups is a streak and not a bar. This fact together with the circumstance that it is frequently present in the female or young and not in the adult, and that the reverse is never (?) the case, would indicate that it is a marking of great antiquity, and bus prob- ably no very great utilitarian significance, except in exceptional cases where natural selection has made use of it for a recognition mark. In general the markings of the head are lateral rather than tranverse. They may be reduced, for the most part, to certain types or modifications and combinations of these. Plate IV represents the various patterns of EVOLUTION OF THE COLORS OE BIRDS. 187 black among North American land birds. Nearly all the characteristic head patterns are produced by the black and white combinations here figured. There are five general types of markings, all more or less simple and rudimentary. They are all lateral, and it seems probable that all transverse markings have been derived from them. I have attempted in this diagram to show how all the head patterns of North American birds are related to these five types. Of course the relations be- tween the widely different forms here associated are not supposed to be genetic, but the diagram is merely in- tended to show, by means of the arrows, how the various patterns may have been derived by the modification of the types. It is not difficult to see why these five pat- terns should be the simplest and earliest developed. In the first place they follow the general trend of the feathers, which would be more natural than to cross it. Then they follow pterylographical areas more or less. It is easy to see how types 1 and 2 might be bounded by the eyes and upper edge of the ear coverts, while type 3 includes little besides the ear coverts. Types 4 and 5 occupy definite feather tracts separated by bare spaces, and their origin is accordingly not far to seek. Poliopiila plumbea is figured as a representative of type 7, which includes also such species as Dendroica striuto, Sitta cfirolinensis and Gcdeoscoptes carolinensis. It is a simple black cap. Type 2, the superciliary stripe or band is illustrated by Zonotrichia coronata, Seiurus aari- capillus and Regulus satrapa belonging in the same cate- gory. The line through the ear coverts, type 3, is the commonest form existing among North American birds. The figure represents Saxicola cenanthe, but the class in- cludes also the following: PsaliripariLS melanotis , Dendroica coronata, Dendroica olivacea, Oporornis formosa, Lanius, Panserina cyanea, besides numerous species where 188 CALIFORNIA ACADEMY OF SCIENCES. this marking is associated with other head markingri, or where it is present but not black in color. The fourth type — the malar steak, represented by Cohipte.'^ aaratufi in the plate, is less commonly met with alone; but type 5, Denchoicd vh'cns in the diagram, which is the throat patch, is very common. There are only a few forms, however, such as Dendroica occiJentalis and Ainj)liisj)iza bUhi-cdta where it occurs as the only black patch upon the head. The combinations of these five types follow next. Fig. 6 is Boulroicii tigriim, which presents. a combination, not of types 1 and 2, but of 1 and modification a of type '1. Fig. 7, Di'iidroica blackhmniuv, is a combination of 1 and 3, the black cap and ear covert. This is a very common form, being presented with greater or less deviation from the type by such forms as (S'(7/« cun- (idens)s,CerthioIa bahamensiN and Pitiingus di'rbianvs. Fig. .S is the combination of types 1 and 4, as shown in ]>endrolcii siriuta. Fig. 9 is a combination of types 1 and 5 illustrated by ParuK utricapillufi. Fig. 10, of AiJiprliN ccdroruin is eijuivalent to 2i( plus 5, and fig- ure 11, Hel iniuthophila chrysojiii'va, equals o plus 5. Fig. lOc, Parus lnulvonicvuj is a combination of types 1, 2 and 5; while fig. 11a, MnlotiltK varin, is a com- bination of types 1, 3 and 5. There is little difficulty in understanding tJiese types and their combinations as markings which have fol- lowed the feathers along natural areas of the birds' heads. They may thus be in part accounted for in ac- cordance with the location of growth force along lines of least resistence, although natural selection has played a not unimportant part in shaping and defining them. Upon leaving the types and considering the various modifications, it becomes immediately evident that here the part played by selection must have been a far more EVOLUTION OF THE COLORS OF BIRDS. 189 important one. Can any law of growth be suggested, for example, for chopping off a black line right through the middle of the ear coverts as in fig. 3a, b and d, and fig. lOs ? By attentively following the arrows, it will be seen how either by the modification or combina- tions of patterns, or both, each form may be derived from some preceding form, more or less completely. Figs. lOe, lie, d, e, alone fail to be reduced to a com- munity with the other patterns. It is unnecessary to encumber the text with the names of the various species, which are not essential to the point under consideration, and may be found in the explanation of plates. A few words should be added concerning the nature of some of the relationships here indicated. By a reduction of the posterior extent of the bl^ck cap in fig. 1, fig. la is pro- duced. A continuation of this reduction would lead to fig. lb; while the cutting ofl' of the front of the black cap would give fig. Ic, which process continued would end in fig. Id. Fig. 2a is hardly more than a narrow- ing of the band of fig. 2, but fig. 26 is a combination of this with fig. 16. In fig. 2c the band has become ex- tended posteriorly abruptly downward, while in 2d the angle is changed and it is extended not merely downward but forward. It will not be necessary to continue an interpretation of all the transitions indicated in the diagram. I desire simply to show that all the head markings of birds can probably be interpreted as modifications of certain fun- damental types which are probably the parent forms from which all have sprung. They are in fact closely allied to the primitive streaked plumage, and may be looked upon as merely an aggregate of streaks in definite parts of the head. It inay now be more readily apparent why some forms of marking never occur while others are so general. It 190 CALIFORNIA ACADEMY OF SCIENCES. is necessary to keep in mind two general influences, the internal forces of growtli regardless of the effect to be produced, and external selection, which looks only at the effect. We have now seen how selection would tend to produce the most striking effects of form and color of marking upon those parts which are most exposed, and especially those parts which are most constantly in mo- tion — the head, throat, wings, tail, rump and under- tail coverts. At the same time, other things equal, these effects would always be produced in the easiest and most natural way, rather than in direct opposition to the laws of growth. With regard to the wing markings, the laws of devel- opment apply when the individual feathers alone are taken into consideration, but the general effect of wing marking is produced in a great variety of ways which has no obvious relation to laws of growth or mechan- ical forces. "Wing markings are generally white in strong contrast to some very dark shade, generally brown, and are obviously recognition marks of some sort. It might be thought that the white was due to de- generation if it uniformly occurred at the tips of the feathers where the wear is the greatest; but in point of fact, while it is very often situated thus, it also occurs at the base or through the middle of the feather. Thus the cedar wax-wing {Ampelis ccJrorii in) has no white wing bars, while the Bohemian wax-wing (Ampelis garridus) which is so closely related, has a wing-bar formed by the white spots at the terminus of the primary coverts, another on the tertiaries, and a vertical line down the wing formed by the white and yellow spots on the outer edge of the tips of the primaries. It surely cannot be held that any internal law of growth, or external me- chanical force which produced such a variety of effects in the one species could have been almost or wholly in- EVOLUTTON OF THE COIX)RS OF BIRDS. 191 operative in a species of the same genus so closely allied. In the rose-breasted grosbeak, the band of white situ- ated apparently in almost the same place as in the wax-wing, is produced not by white terminals on the primary coverts, but by a broad patch of white at the base of the primaries themselves, which is partly cut off by the coverts, leaving only a white band. In the Gal- ifornian woodpecker {Meianerpes forniicivorushairdi) the white markings on several of the feathers run through the center of the primaries leaving both the base and tip uniformly dark. The tail markings also vary in different forms to such an extent as to be inexplicable by any factor but selec- tion. There are, on the other hand, certain points in regard to them which demand an appeal to internal laws for explanation. It is a noticeable fact that the two outer tail feathers have the markings most strongly de- veloped, and that they decrease as we approach the central feather. Of course, it would be said that the outer feathers are the most conspicuous, and the mark- ings would be of more use here than on the inner feath- ers, and this is doubtless the true explanation in such forms as the junco {Junco hyemalis), where only the two outer feathers are thus marked. In the blue jay {Cyano- citta cristata), on the other hand, the tail is marked with a terminal band of white, which diminishes in a regular sequence towards the center. The two central feathers have only a minute tip of white, which would be in- visible even to the closest scrutiny at the distance of a few feet, and hence could not have been produced by selection. This is another example of repetitive marks, it seems to me. Natural selection has developed this white bar on the outer feathers as a recognition mark, and it has been repeated according to the law of corre- lation in a decreasing series toward the center. In the 192 CALIFORNIA ACADEMY OF SCIENCES. course of time these inner marks might become of suffi- cient size for natural selection to make use of, and then they would rapidly increase in size. The tail of the belted kingfisher (Geryle alcyon) is an interesting in- stance of this sort. When the tail is in a normal posi- tion of rest, the two outer tail feathers almost or quite touch. The bars on these two feathers are so symmet- rically placed that they invariably meet, forming one continuous line. On the outer web, just opposite the tip of each bar, is a spot of white. This complex ar- rangement has obviously been due to selection, for by no law of pigment distribution could the bars on one feather be made to match the bars on the opposite feather with such perfect accuracy. On the innermost feather of the tail the bars are present, but so very faint as to be scarcely discernable, and on the successive feathers passing outward they become more and more sharply defined. Certain birds display a curiously converse form of tail marking, having the greatest specialization on the two inner tail feathers. This is markedly the case with some of the woodpeckers, such as Hphyrapicufi varius, which has the outer tail feather barred distinctly on its outer web, and less so on the inner web, this marking repeated but much less complete on the next feather within, followed by two feathers entirely unmarked and with the two inner feathers the most strongly barred of all. Sometimes these two inner feathers are barred on both outer and inner web', the black predominating on the former, and the white on the latter (young); while sometimes the outei- web is black without marks, and the inner web white with narrow bars of black (adult). Of course, this instance is at variance with the rules, but becomes intelligible when it is seen that the inner webs of the upper tail-coverts, and sometimes the entire EVOLUTION OF THE COLORS OP BIRDS. 193 feather, indeed, is white. A conspicuous line of white is thus begun down the middle of the rump and car- ried out on these two tail feathers. As the tail is flat- tened against the tree these feathers would stand out verjr distinctly and a broad line of white would be the result, very characteristic of the bird in question. The barring is of no utility, but a mere repetition of the tendency to forna bars on the outer tail feathers, as is shown by the fact that the bars become obliterated with advancing age, until in highly plumaged individuals these inner tail feathers are almost uniformly black on the outer and white on the inner side of the shaft. RECOGNITION MARKS. We may now consider the subject of color markings from an entirely new point of view. Thus far the question has been looked upon largely, if not entirely, from the standpoint of the dead bird. An attempt has been made to show that both the distribution of pig- ment upon the feather and the formation of general patterns of color were to a greater or less extent de- pendant upon the laws of growth resident within the organism. In considering this problem, however, the ubiquitous natural selection was constantly dogging our footsteps and demanding a hearing, but it is now time to listen to its cause argued by an advocate for its rights and not simply tolerate its presence as a necessary evil. Darwin Avas inclined to attribute the diversity of color in birds rather to the action of sexual selection than to natural selection. Accordingly such instances as the conspicuous white tail of the rabbit he found difficulty in explaining. It is to Wallace that we must turn for an elucidation of the real meaning of these conspicuous colors. He has shown that a large number of color 13 1U4 CALIFORNIA ACADEMY OF SCIENCES. marks, which had been previously thouglit to be of no significance, were in reality of use as a means of recog- nition by the individuals of a species among themselves, or by the individuals of one species of other allied forms. Mr. E. B. Poulton has elaborated and system- atized the various theories of color marks, principally as originally presented by Mr. Wallace, and I will use his classification and terminology as given in his work On the Colors of Animals, merely simplifying it so as to exclude such classes as are not found among birds. His table of colors classified according to their uses may be modified for the present purpose as follows: A. APTATIC COLORS (dei-cilful). Causing an animal to resemble its enTironment, or to be mistaken for some other species. I. Cryptic Colors. Protective and aggressive resemblance. 1. Procriijilk- — Protective. „ , 4 i- 11 f Variable. u,. General pTotective resemblances p , . 6. Special protective resemblance. '2. ^4 ntkryptic — Aggressive. ^1 . 1 1 ( Variable. c. Cieueral aggressive resemblance- ,-, , . °° ( Constant. d. Special. II. P.SEUDOSEMATIC CoLORS. False warning and signaling. 1. Pseudaposematic — Deceptively suggesting something dangerous to an enemy, 2. Pseudepisematic (alluring colors). Deceptively suggesting some- thing attractive to prey. B. SEMATIC COLORS {slunalhig). Warning and signaling colors. I. AposEM.iTic Colors. Warning colors. II. Eplsematic Colors. Recognition marks. 1. Dirvclh-r. ri. Hecognition by distant stragglers. b. In close flight. c. In migrations. 2. Di.scrimiiuilivc. 3. Sexual. 4. Socialistic. d. In darkness of uignt. e. In burrow. /. In care for young. C. EPIGAMIC COLORS. Colors displayed in courtship. EVOLUTION OF THE COLORS OF BIRDS. 195 Let us now consider these various classes and see how they may help in the elucidation of the color problem. Omitting the more inclusive divisions as sufficiently clear, let us commence immediately with (1) Procryptic parts- yellow. . back' plivV green. PINTJS Color olive green.ashyon head, crown chestnut. \ Crown yellow, lores black. Duller. \ OELATA \ Brighter. \. \ CELATA y^ \ \ LT7TESCENS \ \ M Throat yellow. Crown orange brown, color olive- green, CHE.YSOPTBRA Ivower parts.yellow,/ back olive green. LAWEENCEl Crown black BACHMANI Crown yellow. Throat black. No white spots on tail. White spots on. tail WESTEEN Crown yellow. 'Elain oliye green. -PEREGRINA- EASTERN Genus Compsothlypis. The Parula Warbler, etc. (8) Adult male more conspicuously colored than female; young with a peculiar first plumage. Prevailing colors, white, bluish gray, olive green, yel- low, orange brown. EVOLUTION OP THE COLORS OF BIRDS. 325 Sexual selection appears to have been the chief factor in the origination of the color markings of this genus. The orange brown of the breast is an intensification of yellow analogous to that of the crown of Helminthophila celata. The young plumage shows the coloration of the primi- tive bird — dull olive and gray. Genus Dendroica. The Wood "Warblers. (7) Adult male more conspicuously colored than female; young similar to female, or (8) with a peculiar first plumage; or, more rarely, (5) male differs from female in breeding plumage only; young with peculiar first plumage. Prevailing colors, black, white, olive green, yellow, orange, bluish, chestnut. There seems to be little doubt that the varied color markings of this extensive genus have been produced for the most part by the action of sexual selection. As this is a peculiarly favorable genus for the study of the effects of sexual selection I have prepared tables of the . colors of the entire genus, one for the female or imma- ture plumage and the other of the adult males (Plates XVIII and XIX). In order to get the colors of any one species read the colors in a line from right to left, while to compare the colors of the same part of the body in different species read the columns up and down. These two tables illustrate sexual selection, pigment assort- ment, environmental influences, and many less universal points. It will be noticed that although the colors in Plate XVIII are of dull monotonous tints, nearly all the specialized colors are suggested. The general effect of this plate is olive green on the left half and white or yellow on the right. The only conspicuous exceptions to the olive color are the three species in which the rump is 326 CALIFORNIA ACADEMY OF SCIENCES. yellow, and those in which the upper tail coverts are bluish gray. The white and yellow on the right hand side is considerably interrupted by streaks, but in gen- eral is fairly constant except in D. cestiva and its allies. From this it seems undoubted that the ancestor of the genus was an olive green bird, probably streaked both above and below. The olive green is a combination of black and yellow, which were apparently the original pigments of the genus. They were thrown off indis- criminately producing the olive green effect, and the bulk of the pigment following the shaft of the feather would give a streaked appearance to the bird. Excess of sunlight upon the back would cause the greater part of the pigment to lodge there, and the result would be a bird not unlike a composite of the females here repre- sented. Then sexual selection would step in as a factor in pro- ducing change. Occasionally a single feather or a par- ticular spot on the bird would receive a trifle more of either the yellow or the black pigment than usual, from a cause .which, for lack of a better name, we may call fortuitous, and this bird would be conspicuous among his fellows, and more easily gain a mate and leave off- spring. In the course of time this character would be- come exaggerated, from the continual selection, into a specific character. Olive green, black and yellow would then be the three colors of the genus, the back being darker than the breast, and the black and yellow occur- ring upon the most conspicuous parts of the body. It will be noticed from the diagram that these colors occur most frequently upon the top of the head, rump, upper tail coverts, ear coverts, throat and breast, where they would be most noticeable. An intensification of the yellow would produce orange, as in B. blackburnice, while a darkening of this, perhaps by reintroducing black, EVOLUTION OP THE COLORS OF BIRDS. 327 would result in the chestnut of B. bryanti, etc. This leaves only the blue as a doubtful color, although it ap- pears to be related to the black through gray. The following facts, shown by these plates, seem to be inexplicable in any way except by the law of the assort- ment of pigments^ or else this law seems to account for them most satisfactorily: (1) the specialized colors of the males are generally the colors which, when combined, would produce the generalized colors of the females; (2) the specialized colors of the males when combined gen- erally produce the generalized colors of the males; (3) exactly the same color appears in widely separated parts of the body of one species; (4) exactly the same color often appears on the same or on different parts of the body of different species; (5) in general, the same colors run through the entire genus, however differently they may be combined or modified in quantity or distribution. The following details concerning the proportion and distribution of the different colors of the genus in the adult male plumage may be of interest in this connec- tion: Black is present in nineteen out of the twenty- four species, being confined exclusively or mainly to the upper parts of the body in four, and to the lower parts in one species. The top of the head is solid black in four species, the back mainly or entirely so in two, the ear coverts in ten, throat in six, breast in three, and sides in one. Yellow appears in eighteen species, being confined to the upper parts of the body in two species and to the lower parts in eight. The top of the head is yellow in five species, the back never so. The rump ■ is yellow in four, ear coverts in four, throat in nine, and breast in eleven. Olive or olive green occurs in thir- teen species, being confined to the upper parts of the body in all of them. Blue is present in eight species, in all but one of them (B. ccerulea) being excluded from 328 CALIFORNIA ACADEMY OF SCIENCES. the lower parts, while orange or chestnnt are also repre- sented in eight species. The following correlations of color may also be noted: When white appears on the throat or ear coverts it is the color of the breast and abdomen; when the rump is yellow the throat is yellow or white ; when the top of the head is chestnut or orange, the throat is generally the same (one exception); when the top of the head is yellow the throat is generally yellow or white; when the back is streaked the sides are generally streaked. Genus Seiurus. The Water Thrushes, etc (2) Adult male like female; young with a slightly less developed plumage. Prevailing colors, black, white, brown, olive, orange, rufous. The resemblance of Passerella to some of the thrushes has already been mentioned, but the present genus ex- hibits even more perfect similarity to the thrushes, both in color and markings. The orange crown of S. auro- capillus and the greenish olive color of the back in this species are of course exceptions. It would seem that the markings are to be explained largely by the general laws of pigment deposition, the greater amount of pig- ment going to the back has made it uniform in color, while the breast has retained the primitive spotted plumage, the markings having been defined and accent- uated by sexual selection, perhaps. The superciliary stripe is a conspicuous recognition mark, and may have originally been discriminative in character, distinguish- ing the ancestral form of (S'. noveboracensis from the ancestral form of S. aurocupillus with a white orbital ring. The colors of this latter species are similar to the typical colors of the family — black, yellow (orange) and olive green, but the other species are all brown. evolution op the colors op birds. 329 Genus Geothlypis. The Kentucky Warbler, etc. (7) Adult male similar to female (but more con- spicuously colored); young similar. to female, or (8) with a more simple plumage than the adult. Prevailing colors, black, white, ashy, brown, olive green, yellow. The characteristic colors of the family, black, yellow and olive green, are conspicuously present in this genus — the result of pigment assortment. This genus is a particularly good example of the combined action of iso- lation, sexual selection, and climatic influences in the production of different species. Geothlypis has more geographical races than is usual in the family, and these are clearly the result of environmental influences. This is conspicuously the case with the different varieties of G. trichas. Such species as G. melanops and G. beldingi are merely climatic races in which the modification has becorae extreme enough to establish them as distinct from G. trichas. The Mexican yellow throats are dis- tinguished from the Guatemalan species by the eyelid being black in the latter and white in the former. This cannot be solely the result of climatic influence, but is due either to isolation alone or to isolation and selec- tion. The specific distinctions between G. formosa, G. agilis, G. Philadelphia and G. macgillivrayi are due to isolation and sexual selection. G. 'macgillivrayi appears to be a retarded form of G. Philadelphia. Genus Icteria. The Chats. Genus Sylvania. The Hooded Warbler, etc. (8) Adult male more conspicuously colored than female; young with a peculiar first plumage. Prevailing colors, black, white, gray, olive green, yel- low. The colors of these two genera are typical of the 330 CALIFORNIA ACADEMY OF SCIENCES. family, and are to be explained by pigment assortment and sexual selection. Genus Setophaga. The Eedstaets. (7) Adult male more conspicuously colored than female; young similar to female, but duller, or (2) adult male like female, young with a peculiar first plumage. Prevailing colors, black, white, yellow, red, chestnut, brown. The colors in this genus are the result of sexual selec- tion. By pigment assortment the olive green has become entirely replaced by its component black and yellow. The yellow has become intensified into the cor- relative orange or red, and by sexual selection has been located under the wings, where it will be most conspic- uous when the bird is in motion. The female has in- herited the yellow color in place of the intensified red, and the black is replaced by olive gray. As in the orioles where chestnut occurs apparently intimately connected with yellow and intensified red, so here also a species is found (S. miniata) with a crown-patch of chestnut, ap- parently intensified from yellow. In this species the red of the under parts is on the breast, extending down on the belly, instead of on the sides, and is much more intense than in S. ruticiUa. The different species have doubtless been originated by sexual selection and isola- tion in a tropical climate. The fact that in some of the most brilliant species the female is colored like the male is an evidence of a high degree of specialization. Genus Cardellina. Red-paced Warbler. Genus Ergaticus. Red Warbler. (2) Adult male like female; young with a peculiar first plumage. Prevailing colors, black, white, gray, brown, red, vermilion. EVOLUTION OF THE COLORS OF BIRDS. 331 Like Setophaga, these two genera of brilliant red warblers are tropical in their distribution, and the colors have been produced by sexual selection in a hot climate. Genus Basileuterus. Brasher's Warbler, etc. (1) Adult male like female; young like -the adult (?). Prevailing colors, black, yellow, olive green, chestnut, orange-rufous. The colors in this genus are the conventional ones of the family, and are to be accounted for as in the pre- ceding instances. The different species appear to be largely due to climatic influences. FAMILY MOTACILLIDiE. The Wagtails and Pipits. (5) Male in breeding plumage differs from female; young with peculiar first plumage (Motacilla and Budytes), or (4) both sexes change with season; young differ from adults at any season (Anthus). Prevailing colors, black, white, gray, bluish, brown, yellow, olive green. In this family a certain similarity to the colors of the genus Dendroica is to be noted. The bluish ground color is present in some of the species of Motacilla, while in ilf. tnelanope and in the genus Budytes the ground color is olive green, thus presenting the two colors most often occurring in the generalized markings of Dendroica. In this family also black and yellow form the principal specialized marks. Sexual selection has evidently been the factor which has produced the markings in this group, although far less completely carried out than in Dendroica. The terrestrial habits of the members of the family may have had a tendency to suppress the bright colors, Anthus in particular being protectively colored. The gregarious disposition of these 332 CALIFORNIA ACADEMY OF SCIENCES. birds has rendered necessary the white recognition marks -of the wing and tail. FAMILY OINCLID^. The Dippers. Genus Cinclus. The Dippers. (1) Adult male like female; young like adult (young a,nd winter plumage slightly different). Prevailing colors, grayish, brownish, white. The colors are protective, harmonizing with the rocks along the mountain streams frequented by these birds. The white color of the edges of the feathers on the lower parts of the body in young and winter specimens points to an affinity to southern forms, in which the under parts are white. Thus in G. leuoonotus of Colom- bia and Ecuador the entire under parts, head and middle qt back are white. The adult of C. ardesiacus of Costa Rica is very similar to C. Tuexicanus, but the breast of the young is" almost pure white. Why there should be an increase in pigment toward the north in- stead of the reverse, as is the rule, I cannot suggest. FAMILY TROGLODYTID^. The Wrens, Thrash- ers, etc. (1) Adult male like female; young like adult, or (2) young with a peculiar first plumage. Prevailing colors, black, white, slaty, gray, brown, rufous, chestnut. These birds are, as a rule, not highly specialized, so far as their colors are concerned, reminding one of the general plan of color markings among many of the sparrows. As a rule, the back is some shade of brown or rufous, with the breast white, and either the breast alone, or sometimes both back and breast, profusely streaked or spotted. Sexual selection lias had, it would seem, but a subordinate part in producing this plan of EVOLUTION OP THE COLORS OP BIRDS. 333 marking. . Allusion has already been made to the use of the chestnut color of the under tail coverts of Craleo- scoptes as a recognition marking (see ante, p. 203), while the black cap of this genus may serve a similar purpose. The white wing and tail characters are either directive or discriminative marks, and are very generally present. When the adult are specialized beyond the streaked plumage, either by the assumption of a uniform dark color or of a dark back and light under parts, the young show, to a more or less marked degree, the streaked or spotted plumage of the ancestral form. I am unable to suggest any explanation of the barred markings so com- mon on the posterior part of the body among the wrens. FAMILY CERTHIID^. The Creepers. Genus Certhia. The Creepers. (1) Adult male like female; young like adult. Psevailing colors, brown, grayish, white. The colors of this genus are protective in nature, the back harmonizing perfectly with the trunks of the trees to which the bird clings. The breast is white in accord- ance with the general laws of growth. FAMILY PARID^. The Nuthatches and Tits. (1) Adult male like female; young like adult (except in Auriparus). Prevailing colors, black, white, brown, bluish, gray, yellow. The birds of this family are highly specialized, al- though never brilliantly colored. The primitive streaked pattern is almost or completely wanting even in the young plumage, showing that the specialization has been carried very far. Auriparus is the only genus which displays any bright colors, and in this instance the yel- low head is obviously the result of sexual selection. 334 CALIFORNIA ACADEMY OF SCIENCES. being much duller in the female and wanting in the young. How this color can be accounted for in accord- ance with the law of the assortment of pigments I do not see at present, for it would seem that some species in the family should be colored olive green. The different species of the genus Sitta are very distinctively marked. As the sexes are alike it is difficult to decide how im- portant sexual selection may have been in originating these markings and the same is true of Parus. The latter genus has been especially susceptible to the influ- ences of climate, a large number of the species breaking up into geographical races. Psaltriparus is equally in- fluenced by climate. Little inconspicuous marks are generally the most difficult to explain, and this is no- tably the case with Psaltriparus. Of what possible utility can be the brown head as contrasted with the gray back? It is present in both sexes so could hardly be looked upon as the result of sexual selection, nor is it conspicuous enough to be of use as a recognition mark. If, however, some other bird inhabiting the same ter- ritory looked very much like Psaltriparus but without the brown cap, it might serve at close range as a dis- criminative mark. FAMILY SYLVIIDAE. The Warblers, Kinglets, AND GnATCATCHERS. (7) Adult male generally more conspicuously colored than female; young like adult female, or (8) with a peculiar first plumage. Prevailing colors, black, white, olive green, yellow, orange, red, bluish gray. The colors of this specialized family may be explained by sexual selection and the assortment of pigments. The similarity to the Mniotiltidse and Motacillidas in point of coloration is quite strikiag, the olive green, EVOLUTION OF THE COLORS OF BIRDS. 335 black, and yellow being present and also the bluish gray. Phyllopseustes has not progressed beyond the generalized stage of the warblers, no conspicuous sexual ornaments having been added, but the crown patch of Eegulus is a highly developed character. In R. calen- dula the yellow has been completely intensified into scarlet, but in R.satrapa the intensification is less com- plete. This species exhibits the pure yellow and its in- tensification into orange in different parts of the crown. The bluish or black crown patch of Polioptila is prob- ably the result of sexual selection, as it is confined to the male. A remarkably fine illustration of discrimi- native marks is shown in the outer tail feathers of P. plumbea and P. calif ornica, the outer web being white in the former and black in the latter species. FAMILY TURDID^. The Thrushes, Solitaires, Stonechats, Bluebirds, etc. (8) Adult male usually more conspicuously colored than female; young with a peculiar first plumage, or (2) male like female; young like some ancestral stage of adult. Prevailing colors, black, white, brown, rufous, plum- beous, bluish gray, blue. The ancestral form from which this family arose was a brown spotted or mottled bird, as shown by the young of to-day. The different genera have diverged very widely in point of color, however, but may all be ex- plained in accordance with the law of the assortment of pigments. If the primitive pigments were blue and reddish brown their combination would produce Mya- destes, the brown alone would serve for Turdus, while the blue deepened would produce the color of the back of Merula and Hesperocichla, in combination with brown, the back of Cyanecula and Saxicola, and inten- 336 CALIFORNIA ACADEMY OP SCIENCES. sified, the back of Sialia. 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Wilson, Alexander. American Ornithology, Jardine's Edition. WiNDLE, B. C. A. Teratological Evidence as to the Heredity of Acquired Conditions. Journ. Linn. Soc, London, xxiii, p. 448. Yareell, William. Observations on the Laws which appear to influence the Assumption and Changes of Plumage in Birds. Trans. Zool. Soc. of London, vol. i, pp. 13-21, 1835. EXPLANATION OF PLATES. PLATE I. Pigs. 1, 2, 3. Three outer tail feathers of Dri/obaies pubescens, showing individual variation in color marks. Figs. 4, 5. Feathers from the back of Dryobates villosus and D. scalaris, respectively, illustrating the striped and barred pattern. Pig. 6. Frontal feather of Oeothlypis trichas occidenialis in winter plum- age, illustrating acraptosis. The dark edge wears off in spring, leaving the yellow base exposed. Four times natural size. Fig. 7. Feather from back of head of Dendroica occidenialis in winter plumage. The dark edge wears off in spring, exposing the yellow beneath. Three times natural size. Fig. 8. Feather from breast of Scolecophagus caroUnus in winter plum- age. The light rusty edge wears off in spring, leaving the black exposed. Natural size. Fig. 9. Feather from the back of Plectrophenax nivalis in spring plum- age, the white having worn down and left the black base remaining. Fig. 10. Feather from the back of Plectrophenax hyperboreus in spring plumage, the white tip remaining unworn. Fig. 11. Feather from the throat of Icterus cucullatus nelsoni, changing from yellow to black by the accession of pigment without moult. Twice natural size. Fig. 12. Feather from the back of the head of Icterus bullocki, showing the change from yellow to black by the accession of black pigment. Twice natural size. PLATE II. Feathers illustrating the stages of transition to a completely black mode of pigmentation. Natural size. Figs. 1-6, inclusive. Changes from a streaked plumage. From the under parts of Melanerpes formicivorus bairdi. Figs. 7-13, inclusive. Changes from a streaked to a barred, and from a barred to a completely black feather. From the under parts of Sphyra- picus varius. Figs. 14-17, inclusive. Changes from a barred to a black stage. From the edge of the throat-patch of the female Sphyrapicus thyroideus. 346 CALIFORNIA ACADEMY OF SCIENCES. PLATE III. Feathers of the wing of Falco sparverhis, showing transition of pattern according to successional taxology. Natural size. PLATE IV. Heads of various North American birds, showing types of black mark- ings, with their combinations and modifications. Fig. 1. Polioptila plumbea; a, Leucosiicte griseonucha; b, Melospha geonjiana; c, Peirochelidon lunifrons; d, Coccolhraustes vespertinus. Fig. 2. Zonotrichia coronaia; a, Cyanocephalus cyanocephalus; b, Spi- zelld socialis; c, Ceophl(eiis pileaius S ; d, Cyanociita cristaia. Fig. 3. Saxicola oencmihe; a, Geolhlypis trichas; b, Dendroicadominica; c, Dendroica ca^anea; d, Dendroica pensylvanica; e, Hesperocichla ncevia. Fig. i, Colaptes auratus; a, Passerina cyanea; b, Icteria virens; c, Ceophlceus pileaius $ ; d, Sphyrapicus varius. Fig. 5. Dendroica virens; a, Helminthophilabachmani; h, Xanthocephalus xcmthocephalas; c, Guiraca ccerulea; d, C'ardinalis virginianus; e, C'ardinalis cardinalis ignetis. Fig. U. Dendroica iigrina; a, Zonotrichia leucophrys; b, Zonotrichia leticophrys intermedia; c, C'ampephilus principalis S ; d, Dendroica ccerules- cens. Fig. 7. Dendroica blackhurnice; a, ffiite canadensis; b, Dryohates pubes- cens; c, F?>eo atricapillus; d, Dendroica maculosa; e, Spinus psaltria mexicana. Pig. 8. Dendroica striata; a, Dryobaies borealis; b, Dendroica chryso- paria; c, OaTnpephilus principalis^ ; d, Calcarius lapponicus. Fig. 9. Parus atricapillus; a, Spinus laiorencei; b, Motacilla alba; c, Sylvania mitrata; d, Calcarius ornatus; e, Calcarius pictus. Fig. 10. Ampelis garrulus; a, Parus gambeli; b, Melanerpes formici- vorux bairdi^ ; c, Melanerpes formicivorus bairdiS ; d, Xanthoura luxuosa; e, Otocoris alpesiris. Fig. 11. Helminthophila cArysoptera; a,, Mniotiltavaria; h, Picusvillosus; c, (.'olinus virginianus texanus; d, Callipepla californica; e, Cyrtonyx monte- znmce. PLATE V. Examples of yellow and red as correlative colors. [ The names Icterus cucullatus and /. cucullcUus nelsoni should be transposed.] PLATE VI. The upper figure shows the effect of environment in bleaching color in the genus Myiarchus. The lower figure shows a tail of an immature male Icterus cucullatus nelsoni changing from yellow to black by the accession of pigment without moult. Natural size. EXPLANATION OP PLATES. 347 PLATE VII. Three races of Spinus psaltria, showing the change from a greenish olive to a black plumage. Natural size. PLATE VIII. Three outer tail feathers of Pipilo, showing decrease in size of white markings toward the west and northwest. PLATE IX. Geographical distribution of Sphyrapicus. A. — 1, S. varius; 2, S. varius nuchalis. B. — 8. ruber. Geographical distribution of Pipilo. A. — 1, Pipilo eryihrophthalmus; 2, P. eryihrophthalmus alleni. B. — 1, P. maculatus; 2, P. maculaius arc- ticus; 3, P. maculatus megalonyx; 4, P. maculatus oregonus. PLATE X. Geographical distribution of the races of Megascops asio. 1, asio; 1, flor- idanus; 3, maccallii; 4, trichopsis; 5, bendirei; 6, Jeennicottii; 7, maxwellice. Geographical distribution of Cyanocitta. A. — 1, C. crisiaia; 2, C. cristaia florincola. B. — 1, C.stelleri; 2, 0. stelleri frontalis; 3, O. stelleri annectens; 4, C. stelleri macrolopha; 5, O. stelleri diademata; 6, C. stelleri coronata. PLATE XI. Geographical distribution of the races of Dryobates villosus. A. 1, leu- comelas; 2, villosus; 3, audubonii; 4, maynardi. B. — 1, harrisii; 2, jardinii. Geographical distribution of the ladder-backed forms of Dryobates. A. — 1, D. scalaris; 2, Z>. scalaris parvus: 3, Z> . scalarisbairdi; i, D. scalaris lucasanus; 5, D. scalaris sinaloensis; 6, D. scalaris graysoni. B. — D. nut- tallii. C. — D. borealis. PLATE XII. Geographical distribution of Bubo. A.- — 1, B. virginianus; 2, B. virgini- anus saiuratus; 3, B. virginianus arcticus; 4, B. virginianus subarcticus. B. — B. mexicanus. Geographical distribution of Ohordeiles. A. — 1, C. virginianus; 2, C. vir- ginianus minor; 3, C virginianus henryi. B. — C. texensis. PLA.TE XIII. Map of North America, showing the influence of climate upon the color of Melospiza/asciata. The breeding range of each race is indicated, the territory occupied by each variety being colored as nearly as possible in harmony with the markings of the back. 348 CALIFORNIA ACADEMY OF SCIENCES. PLATE XIV. The shoulders of the different species of Agelaius, showing the transi- tion from the unmodified brown of the female in winter to the adult male plumage in summer. Natural size. PLATE XV. Heads of the different species of Sphyrapious, showing the transition from the brown plumage of the young, through successive stages of in- creasing red, to the adult male of S. ruber. PLATE XVI. Heads of the female and young of the genus Icterus. PLATE XVII. Heads of the adult males of the genus Icterus. PLATE XVIII. Color chart of the undifferentiated plumage, female or young, of the genus Dendroica. For description of a single species, read the lines from right to left; for comparison of the same part of the body, read the columns. PLATE XIX. Color chart of the specialized plnmage, adult male in spring, of the genns Dendroica. [Note. — In one or two instances the colors in the above charts were supplied from descriptions; otherwise, from specimens.] INDEX Acanthis 163, 218, 299 Acceleration, Cope on, 73; instance of Cope's law of 169, 219 Accipiter 268 velox 277 Acquired characters, on the Inheritance of, 2-50; Galton on inheritance of. 5; Kyder on inheritance of, 19; con- sequences of dispensing with in- heritance of, shown hy Cunning- ham, 27 ; inheritance of.by protozoa admitted, 28; Morgan on inherit- ance of, 29 ; Elliot on inheritance of, 38; three evidences of inherit- ance of, as given by Spencer, 43 ; inheritance of, 1st and 3d evi- dences in proof of, as given by Spencer, criticized by Romanes and ' Ball, 43-14 ; transmission of diecussed, 29 : transmission of, di- vided into two classes, 34; Japanese goldfish experimented with by Dr. Wahle, 34. Acquired habits; inheritance of, be- lieved in by Darwin, 40; inherit- ance of, criticized by Ball, 40; in- heritance of, supported by Rom- anes, 41-42. Acraptosis, definition of, 136; instances of acraptotic feathers 135, 136, 137 Acroptosis, definition of 135, 137 ^gialitis , 197 semipalmata 197 Esthetic taste in birds, explanation of, 93-95; Poulton's views on, 93-95; opposed by Morgan, 95-96; Bom- aues on, 97-98; Allen on, 100; Mor- gan on, 101. Agelaius 143, 146, 218, 220, 255, 292 gubernator 178,220,254, 255, 292 phceniceus 185, 220,254, 255, 292 tricolor 178, 220, 254, 255, 292 Alaudidse 287 Albinism, theory of, suggested by Stej- neger 226 Alcedinidse 278 Allen, Grant, on ffisthetics 100 Allen, Harrison, on pigment 182 Allen, J. A., on geographical distribu- tion as factor in evolution of colors 247 Ammodramus 215, 233, 304 maritimus 304 nigrescens 1 51 sandwichensis 304 alaudinus 184, 253 bryanti 253 savannarum passerlnus. . , 184 AmpelidsB 316 Ampelis 216, 217, 236, 316 cedrorum 188, 190, 316 garrulua 190, 316 japonicus 316 Amphispiza 180, 216, 307 belli 254, 307 nevadensis 254, 307 bilineata 188, 254. 307 Anabolism definition of, 68; as factor in pigmentation 163 Anis 276 Anthus 204 Anticryptic colors, defined 194, 197,198 Antrostomus 207 carolinensis 186, 208 cubanensis 208 macromystax 208 vocif ems 208 arizonee 208 Aphelocoma 158, 215, 289 californica 186 sieberii 254 sumichrasti 254 Aposematic colors, defined 194, 200 Aptatlc colors, defined 194 Aptosochromatism, definition of.. .135, 137 Aquila 270 Archibuteo 236, 269 lagopus sanctijohannis 147 Aristotle, originator of doctrine of evolution 2 Asturina 270 350 CALIFORNIA ACADEMY OF SCIENCES. Atthis 236 Attidse, habits of, as proof of sexual selection 88 Auriparus 236 Ball, criticism of Darwin's instancea of acquired habits, 40; criticism of Spencer's evidences of inheritance of acquired characters, 43-44. Baaileuterus 331 Bathmism, definition of 65 BecardB 157 Beckham, on pseudepisematic colors, . 199 Beddard, opposed to sexual selection, 88; on sexual coloration, 89-90; on color in birds, 138; on effects of food on color, 226; on influence of light on pigmentation, 230; sum- mary of Camerano's system of geo- graphical colors, 238; on protective mimicry, 239. Belt, suggestions on natural selection as originator of species ..^ 11-1 Bernicla magellanica, instance of high coloration in female 90 Bilateral symmetry, explanation of . . . . 79 Blackbirds 203, 295 red-winged . . . .143, 154, 178, 185, 220, 292 rusty 136 yellow-headed 155, 291 Bluebirds 203, 213, 222, 229, 335 arctic 157 Boboli nk 149 , 152, 185, 290 Bobwhite 185, 257 Bonasa 260 Boreal genera, Wallace's list of 236 Brooks, modification of doctrine of pangenesis, 5; secondary laws of variation, 62; laws of variation crit- icized by Gulick 72 Brown birds, colors of, protective 196 Brown creeper, protective coloration of 197 Bubonidro 273 Bubo mexicanus 253, 254 virginianus 243,253,254, 274 arcticus 152 subarcticus 210 Bunting, lark 152,179,313 indigo 157,222 varied 311 Butcher-birds 216 Buteo , 269 abbreviatus 147 albicaudatus 206 borealis 160,206, 269 calurus 179 Buteo f uliginoBUs 147 harlani 147 latissima 206 lineatus 269 swainsoni 147, 150, 206 Calamospiza 236, 313 melanocorys 146, 152, 179, 218 Calcarius 218, 303 lapponicus 254 ornatus 149 pictiis 254 Callipepla 236, 258 cali f ornica 258 squamata 258 Camerano, system of geographical col- ors summarized by Beddard — 238, 239 Campephilus 280 principalis 146 Canaries, color of, changed by food 228 Caprimulgidae 207, 283 Caracara 272 Cardinalis 153,221, 310 virginianHs 157, 243 Cardinella 330 Carpodacus 163, 297 casslni 254 erythrinus grebnitskii 297 mexicanus 244 frontalis.. 136, 156, 184, 195, 229, 244 purpureus calif ornicus . . . . , 254 Catbird 182 Cathariata -itrata 146 CathartidEB 267 Cathartes aura 146 Catherpes 236 Cellular continuity, upheld by Morgan, 19-20; upheld by Eimer, 20. Centrocercua 236, 262 Centrouyx 236 Ceophloeus 280 pileatus 147 Certhia 236, 333 famlliaris americana 197 Certhiidffl 333 Certhiola 318 bahamensis 18S Ceryle 278 alcyon 175, 192. 198, 210, 278 amazona 279 cabanisi 279 inda 279 superciliosa 278 torquaius 279 Chachalacaa 265 Chsetura 215, 283 Chamrea 236 INDEX. 351 Chats 329 yellow-breasted 215 Ohelidon 314 erythrogaster 216, 219 Chondestes 180,216,236,304 grammacus 217 Ohordeiles 207,210 texensis 253, 255 virginiamis 255 henryi 185,253 Chuckwill's widow 186 CincHda 332 Cinclus 332 ardeslacua 332 leuconotus 332 mexicanus 218, 219, 332 Circus 268 hudsonicus 206 Clivicola 315 riparia 215 Coccothraustes 296 vespertinus 167, 221 Coccyges 275 Coccyzus 276, 277 americana 277 erythrophthalmus 277 maynardi 277 minor 277 Coerebid* 318 Coues' Key, table of characters of Hel- minthophila 324 Cognate colors, definition of 152 Colaptes 280, 281 auratus 282,155, 156,182 cafer 155, 156, 173, 176, 203 Colinus 257 graysoni 258 ridgwayi 185 virginianus 185 cubanensis 146 floridanus 258 Colors, classification of, by Poulton, 194; definition of aptatic, cryptic, procryptic, anticryptic, pseudose- matic, puesdaposematic, pseudep- isematlc, sematic, aposematic, episematic, directive, discrimina- tive, sexual, socialistic, epigamic, 194-210. Colors, geographical distribution as factor in evolution of, 234: Beddard summarizes Camerano's system of geographical, 238-239; J. A. Allen on, 247, Color in birds, general principles of, 137; Beddard on, 138; theory of, 138-139. Colors in North American Genera, pro- portion and distribution of, 143- 144; black contrasting with white breasts, 148; black with yellow or browu nnder parts, 148; black with rose patch on breast, 148; upper parts black, under parts light col- ored, 148; lower parts and top of head, black, 149; on ways of assum- ing a black plumage, 150, 151. Color, Garman on variation in colors of animals, 231 Color, variation of, with sex, age or season, 211; Darwin on, 212, 213. 215 ; effects of food on, 226, 227, 228 . Columbia 265 Columba fasciata 205 Compsothlypis 324 Concentration, law of, 64 ; definition of, 77. Contopus 215 Cope on retardation, 26-26; definition of Bathmism, 65; on law of extent and density, 66; on laws of acceler- ation and retardation, 73; on four laws of structure, 77-78; instance of law of retardation, 169. Correlation of growth, definition of — 79 Correlative colors, definition of 164; instances of, 155-157; exceptions to, 157. Corvidro 288 Corvus 146, 215, 236 cryptoleucus 162, 290 Cowbirds 290 Cracidse 266 Creepers 333 brown 197 honey 318 Crossbills 156 298, 219 Crotophaga 276 ani 146 sulcirostris 146 Crows 203, 212, 215, 288 Cryptic colors defined 194 Cuckoo 198 American 277 CuculidBB 275 Cuculus canorus 276 552 GALIFOKNIA ACADEMY OF SCIENCES. Cunningham, criticism of pammixis, 23 ; consequences of dispensing with inheritance of acquired char- acters, 27; on natural selection, 28; criticism of "Weismann's observa- tion on feet of Chinese ladies, 31; environment discussed by, 37; ex- periments on effect of light on pig- mentation, 230. Cupidonia 236 Cusp growth, Oshorn on, as evidence of the inheritance of acquired characters, 47. Cyanecula 335 Cyanocephalus 215 cyanocephalus 158, 289 Cyanocitta 158,215, 245, 250 cristata 182, 191, 245 stelleri 245, 246 frontalis 246 table of specific and varietal char- acters of 247 Cyanospiza ." 236 Cypseloides 283, 284 Cyrtonyx 236, 259 montezumee 259 ocellatus 259 salleei 259 Darwin, acceptance of principles of uso and disuse and environmental influences, 3; hypothesis of pan- genesis, 3; on disuse, 25; on ac- quired habits, 40; instances of in- heritance of acquired habits criti- cised by Ball, 40-41; acquired habits supported by Romanes, 41; origin- ator of theory of sexual selection, 80; description of preferential mating, 81-82; theory of sexual selection, 82: Wallace opposed to hia theory of sexual se}ection, 82- 83; on physiological selection, 112; on color variations, with sex, age or season, 212. Death, Weismann's explanation of, 8-9; Morgan's criticism of Weismann's explanation, 9. Dendragapus 204, 205, 259 canadensis 204 f ranklinii . ; 204 obscuruB 204 fuliginosus 204 richardsonii 204 Dendroica 232, 325 JBsti va 157, 221, 326 auduboni 203, 218, 219 Dendroica blackburnise... 148. 188, 221, 326 bryanti 327 cffirulea 158,221, 319, 327 cffirulescens 221 castanea 185, 222 coronata.158, 182, 184, 187. 203, 218. 219 dominica 182, 215 maculosa 148,218, 219 nigrescens 216, 217, 218 occidentalis 136, 188, 221 olivacea 187 palmariim 218, 219 peusylvauica 222 striata 187. 188, 222 tigrina 188, 222 townsendi 221 Tigorsii 221 virens 188. 221 Dickcissel 312 Dicrurua 198 Dippers 332 Directive colors, definition of, 194, 201 ; classification of by Todd, 201; new classification of, 202. Discriminative colors, defined 204, 205 Dolichonyx 290 oryzivorus.. .142, 152, 181, 182, 185, 218 Doves, mourning 205 white-fronted 205 wbite.winged 205 Drongo cuckoo 198 Dryobates . . 179, 224, 244, 252, 280 arizonfe 254 pubeecens 175,181.211, 254 gairduerii 254 Bcalaris 254, 282 bairdi 254 stricklandi 254 villosus 252 , 282 harrisli 254 jardinil 253 leucomelas , 254 maynardi 252 Dyer, objections to physiological selec- tion, 123; objections to the term segregation of the fit, 123.' Eagles 270 Ectopistes 236 migratorius 205 Eimer, on continuity of body cells, 20; instances of observed cases of transmission of mutilations, 32 ; on pigmentation, 162; on general pat- terns of bird colors, 179; on en- vironment in evolution of colors, 226. INDEX. 353 Elauoides 267 f orficatus 152 Elanus , 267 leucurus 152 Elliot, address en Inheritance of ac- quired characters, 88-40. Embernagra 308 Embryogenesis, definition of by Weis- mann 16 Empidias 236 Empidonax 215 Engyptila alblfrons 205 Environmental influences, first recog- nized by Hilaire, 2, Morgan's in- stances of, 35; discussed by Cun- ningham, 37; direct influences of on colors of birds and insects, 238 et seq. Environment in evolution of colors, direct inflaence of, 226; Eimer on, 226. Epigamic colors defined 194, 211 Episematic colors defined 194, 200 Ergaticus 330 ruber 153, 157 Euetheia 312 bicolor 146, 149 Euphoniaelegantissima 158 Euspiza 236 Evolution, history of the doctrine of, 2; laws governing, 64-66; relation of to species, 106. Falco 271 colurabarius 243 suckleyi 147, 271 islandus 152 peregrinus 243 sparverioides 271 sparverius 206, 271 FalconidsB 267 Falcons 271 Fecundity, segregate, definition of 131 Finch, pine 145, 801 purple 297 scarlet rose 297 Flickers 156 red-shafted 173, 176, 203 Flute bird 152 Flycatchers, crested 266 fork-tailed 155 scissor- tailed 165 shiny-crested 152, 196, 204 tyrant 285 vermilion 157, 177 Fringillidse 296 Galeoscoptes carollnensis 182, 187 23 Gallinae 257 Galton, on the continuity of the germ plasm and the inheritance of ac- quired characters, 5; on physiolog- ical selection, 115. Garman, on the influence of light upon the colors of animals 231 Geddes and Thomson on katabolism and anabolism 68 Genealogical table of Spinus and ]its allies, 300; of Helminthophila,324. Geococcyx 215, 276 Geothlypis 243. 329 agilis 221, 329 beldingi 329 f ormoda 329 macgillivrayi 221, 329 melanops 329 Philadelphia 221, 329 trichas 167,182,218, 329 occidentaUs 135 Geratology, definition of, 78; example of, 227. Germ-plasm, continuity of, criticized Vines, 13-14; "Weismann's reply to Vines, 15; Ryder on, 18. Gnatcatchers 334 blue-gray 168 Goatsuckers 283 Gold-finches 145, 195, 300 green-backed 150, 195 pine 299 Goose. Upland 90 Goshawks 268 Mexican 270 Grackles 229, 296 Grassquit 149, 312 Greenjay 168 Grosbeaks 311 blackheaded 155 cardinal , 157 evening 296 pine 296 rosebreaBted.148, 155, 176, 184, 191, 222 Grouse 204, 259 Canada 204 dusky 204 Franklin's 204 Eichardson's 204 ruffed 260 sage 262 sharp-tailed 262 sooty 204 Guiraca csrulea 158, 218 Gulick, criticism of Brooks' laws of variation, 72; on isolation, 125-128. 354 CALIFORNIA ACADEMY OP SCIENCES. Gymnokitts 236 Habia 221, 311 ludoTicians 148,154, 165, 176,223 melanocephala 155 Haeckel, explanation of views of Ln- marck and Hilaire, 2-3; plastidule theory, 6; laws of heredity, 69, 79. Haliieetus 236,270 Harporhynchus 236 Hartog, difficulty iu Weismann's the- ory of variation 66, 57 Hawk , broad-wi nged 206 Harris's 269 marsh 268 Mexican black 270 red-tailed 206 sparrow 165, 206 Swainsou's 206 western red-tailed 179 white-tailed 206 Helinaia 320 Helmiutherus 236 Helminthophaga 236 Helminthophila 321 celata 322 lutescens 243 chrysoptera 188, 221,322 Iflwrencei 322 leucobronchialis 322 luciffi 217, 322 peregrina 321 pinUB 221, 322 ruflcapilla 221, 322 awainsoni 218 Helmitherus 320 Heredity, influence of, 25 ; laws of 79 Hepperocichla 336 nsBvia 182, 186, 203 Hilaire, originator of the doctrine of environmental influences 2 Hirundinida 314 Homology, explanation of by Cope 77 House-finch 86, 136, 166, 196, 229, 244 Humming-birds 221, 284 Hyatt on geratology 78 Hybrids, asymmetrical 174 lateral 174 symmetrical 174 Hybrid feathers, use of, 172; classifica- tion of, 174. Hylatomus 236 Hypercbromism, from environmental influences 241 Icteria 236, 329 virens 216 Icteridffi 290 Icterus 167, 221 buUocki 149. 294 cucuilatus 156, 292, 293, 295 igneus 156 nelsoni 133, 166, 291, 294 galbula 149 , 294 pariaorum 148, 295 spurius 148, 294, 296, 310, 319 Ictinla 267 Idioplasma, distinctions concerning made by Weismann 16 Immortality of protozoa, explanation of by Weismann, 8-9; admitted by Vines, 11. Isolation, Gulick on 126-128 Jackrabbit, black 71 Jay, blue 141,191,245, 260, 288 California 186 Johnson, on plumage changes in Ic- terus 133 Junoo 180, 204, 216, 217, 191, 236, 306 annectens 254 canicepa 264 cinereus dorsalia 254 hyemalis 147,148, 177, 191 Katabolism, definition of, 68; as factor in pigmentation, 163. Kingbird 143, 156, 199, 217, 265 gray 156 thick-billed 156 King-crow 198 Kingfishers 212, 278. 279 belted 176,192, 198, 210 Kinglets 334, 199 golden-crowned 156 ruby-crowned 143, 166 Kites 267 Ladder-backs 253 Lagopus 236, 260 lagopus allenl 134 leucurua 261 rupestris 261 atkensis 261 nelsoni 261 reinhardti 261 welchi 261 Lamarck, originator of the principle of use and disuse 2 Lanidee 317 Lanius 187, 216, 218, 236 Lark-finch 216, 217 Larka 287 hornedj 196, 260, 287 Leucoatiote 163, 218, 236. 298 atrata 147 Linota 236 INDEX. 355 Longspurs 303 cheatnut-colored 149 Lophophanea 236 Lophortyx 236 Loxia 218, 21 9, 236, 298 leucoptera 298 Lunda cirrhata 200 Macroohires 283 Macronyx amelisB 240 croceuB 240 Magpies 152, 216, 288 Melanerpes torquatus 216 Markings, olasgiflcation of patterns of, 169 ; Elmer on patterns of bird col- ore, 179. Martins 314 purple 149 Meadowlark..l56, 175, 178, 203, 211, 240, 293 Megoscops asio, 250; table of races of, showing relation of color, 250. asio maccallii 254 flammeolus 264 trichopsis 264 Melanerpes 280 aurifrons 223 carolinus 222 erythrocephalus..l45, 153, 216,217, 218 forraicivorua bairdi..l43, 170, 173, 175, 181, 191 Melanistlc plumage, methods of, as- suming, 161; theory of, suggested by Stejoeger, 226; Spinus psaltria as an instance of the assumption of, 241; instances of noted by Ridgway, 243. Meldola, criticism of Romanes theory of physiological selection, 115; Bo- manes' reply to, 115-116. Meleagris 236, 263, 264 Melopelia leucoptera 206 Melospiza 196,215,235,236,250, 308 cineria 249 fasciata 248 fallax 248 heermanni 248 moutana 248 rufina 248, 249 samuells — 248 Merriam, on plumage changes, 134; on geographical distribution and North American faunal areas, 234, 235. Merula. . . : 335, 336 confinis . 336 migratorlapropinqua 217 *Metflbolism, explanation of, 67-68; as explanation of pigmentation, 163. Micrathene 236 Micropodldse 283 MicropuB 284 Milvulus 285 forficatus 163, 165 tyrannus 155, 286 Mimicry, Stejneger on, 198; Beddard on protective, 239. Mimus polyglottos 183 Mniotilta 236, 320 varia 151,162,221, 388 MniotiltidsB 157, 319 Mockingbird 183 Molothrus 290 seneus 146, 291 ater 146, 222 Morgan, criticism of hypothesis of pangenesis, 5-6; criticism of Weis- mann's explanation of death, 9; Weismann's theory of heredity op- posed by, 17; on cellular continu- ity, 19-20; criticism of panmixis, 22; on inheritance of acquired characters, 29-30; transmission of mutilations discussed by, 30; in- stances of environmental influ- ences, 35; suggests modification of Spencer's theory of physiological u,Qits,'58; explanation of preferen- tial mating, 81; opposed to Poul- ton's views of the aesthetic tastes of birds, 95-96. Motacilla melanope , 331 Motacillidfe 331 Musci vora mexicana 199 Mutilations, transmission of discussed by Morgan, 29-30; transmission of discussed by Weismann, 30-31 ; Eimer on observed instances of, 32. Myadestes 335 townsendii 204, 217 Myiarchus 256 cinerascens 256 crinitus 256 lawrenceii 243 mexicanus 256 nigricapillus 243 Myiodioctes 236 Myiodyuastes 285 Naegeli, on the existence of a nucleo- plasm first developing into body cells , then becoming simplified into reproductive cells, 10. 856 CALIFORNIA ACADEMY OF SCIENCES. Natural selection, discussion of by- Cunningham, 27-28; argued against as not creative, by Schurmann, 51; conditioned by variation, 62-53; further discuasiou of, 106-107, 110; Komanes on, as originator of spe- cies, 113-114; suggestions on as originator of species, by Belts , 114; as originator of species up- held by Meldola, 115. Nelson, E. W., on Plectrophenax ni- valis 301 Neocorys 236 Nighthawk. western.. .185,196, 207, 210, 254 Nuthatches 333 Nyctala 236 Nyctea nyctea 152, 198 Nyctidromus 207 Oporornis 236 f ormosa 187 Oreortyx 236, 258 Oriole 293 Arizona hooded 133, 156 fiery 156 hooded 156 Oroscoptes 236 Ortalia 265 Ortyx 236 Osborn, on laws of cusp growth, 47; criticised by Poulton, 17; reply to Poulton's criticisms, 48. Osprey 272 Otocoris 218, 250 Owl, barn 273 burrowing 197, 210 great horned 254 horned 273 screech 250 snowy 198 western horned 210 Pammixis, Weismann's explanation of, 22; criticism of by Morgan, 22; criticism of by Cunningham, 23; Romanes' explanation of, 23; Ro- manes' theories on, 24-25; Cope views in regard to, 26. Pandion 272 Pangenesis, Darwin's doctrine of, 3; explanation of by Romanes, 3-5; modification of by Brooks, Galton. Herdman, etc., 5; criticism of by Morgan, 6-6. Parabuteo 269 unicinctus harrisi 147 Parallelism, Cope on laws of 78 Parauque 207 P.aridffl 333 Parrots 212, 274 Partridges 237 Partridge, massena 259 mountain 258 Parula americana 221 Parus 236 atricapillus 188 budsouicus 188 PasserculuB 236 Passer domesticus 209 Passerella 196, 215, 236, 308 iliaca 308 megarhyncha 254 unalasohcensis 254, 3 J8 Passerina 222, 311 cyanea 157, 187, 222 versicolor 153 Peckham, Prof, and Mrs., description of sexual selection among the At- tidae 88 PediocEetes 236, 262 Perisoreus 215, 236, 289 Petrochelidon 314 lunifrons 216, 218 Peuceea 180, 196, 216, 307 cassini 254 mexicana 254 Phsenopepla 236 Phainopepla 317 nitens 146, 152, 204, 221 PhalasnoptiluB 207 Phalaropes 220 Phasianidfe 263 Pbylogenic extent and density, explan- ation of 66 Physiological units, Spencer's theory of 6-7 Physiological selection, 110; Romanes on, 110-112; Darwin on, 112; sug- gestions on by Galton. 115; objec- tions by Wallace, 116-117; objec- tions by Wallace answered by Ro- manes, 118-119; further discussion of, 120; Seebohm's criticism of, 120-123; summary of, 124-125. Pica 215, 236 nuttalli 289 pica hudsonica 146 Pici 279 Picicorvus 215, 236 columblauus 289 PicidfB 279 Picoides 179, 223, 280 Pious pubescens gairdneri 243 villosus harrisii 243 INDEX. 357 Pigmentation^ definition of, 139; Elmer on, 162; Beddard on Influence of light on, .230; influence of light on, experiments by Cunningham, 230; experiments , hy Poulton on effect of light on, 230, 231. Pigment, definition of, 139; law of as- sortment of, 139-142, 145; law of growth force in regard to distribu- tion of , 159-160; Elmer on distri- bution of, 162; Dr. Harrison Allen on. 182; metabolism as factor iu distribution of, 163. Pigeons 204, 265 band-tailed 205 passenger 205 Pinicola 153, 236, 296 enucleator 154, 221 Pipilo 180, 216, 236, 309 chlorurus 309 erythrophthalmus 147, 148, 216 222, 250, 309 alleni 251 aberti 254 f uscus 309 crissalis 182, 203 maculatus 147, 148, 216, 250, 309 arcticus 251, 262 megalonyx 251 mesoleucus 254 oregonus 251 Pipit 240, 331 African 240 Piranga aestiva 221, 243 erythromelas 143, 160, 153, 180, 222 hepatica 163 ludoviciana 180, 222, 150, 157 rubra 153. 222 Pitangus , . ; 285 derbianus 188 Platypsaris, exceptions to correlative coloration 157 Plectrophenax 218, 301 hyperboreus 152, 302 nivalis 136, 152, 301 Plectrophanes 236 Plover, golden 133 Plumage changes, explained by Yar- rell, 132, 136; Merriam on, without moult, 134;. in breeding season, 136; classification of , 137. Polioptila 209 caerulea 158 californica 353 plumbea 187. 335 Polyborus ,272 cheri way 272 lutoaus 27,2 Poocsetes 303 Pocecetes 236 Poulton, criticism of Osborn's evi- dence of the inheritance of ac- quired characters, 47; Osborn's re- ply to Poulton, 48; criticism of Wallace on sexual selection, 84; on £6sthetic taste in birds, 93-95; crit- icized by Morgan, 96-96; on gen- eral principles of color, 137-138: classification of color marks, 194; on effect of light on pigmentation, 230-231. Praeger, instance of procryptic colors. 197 Prairie hens 261 Preferential mating, Darwin on 81, 82 Procryptic colors defined, 194, 195 ; Praeger's example of, 197. Procyon lotor 210 Progne 314 subis 146, 150, 221 Protonotarla 320 citrea 221 Psaltriparus 236, 334 melanotis 187 Pseudaposematic colors 194, 199 Pseudepisematic colors, 194-199 ; Beck- ham on, 199. Pseud ogryphus californianus 146 Pseudohybrids, definition of, 174, 177 Pseudosematic colors 194, 198 Pseudozoorubin 138 PsitacidEe 274 Ptarmigan 134, 195, 260 Puffin, tufted 200 Pyrocephalus rubineus 153, 222 mexicanus 141, 157, 177, 286 Pyrrhuloxia 236. 310 sinuata 154, 181 221 Quail, valley 258 Quiscalus 146, 221. 229, 295 Raptores 266 Eaven, white- necked 152 Recognition marks, 193; classification of, 194; Wallace on, 200-201. Redpolls 299 Redstart 330 American 147 Regulus 236 calendula 153 335 182, 187, 335 olivacea 143 358 CALIFORNIA ACADEMY OF SCIENCES. Bepetitive marks 171 Reproductive cells, immortality of among matazoa, 10; simplicity of confirmed by Spencer, 17. Retardation, explanation of by Cope, 25-26; definition of, 73; instance of Cope's law of, 169, RhynchopLanes 303 Ridgway on relation between color and geographical distribution in North American birds, 2il ; in- stances of melanism 243. Roadrunners , 276 Robin varied 203, 217 Rock-thrush 81 Romanes, explanation of Darwin's ho- pothesis of pangenesis, 3-5; on cessation of selection, 23: theories on pammixis, 24-25; on inherltence of acquired characters, 28; exam- ples of instinct due to transmis- sion of acquired characters, 41; supports Darwin's theory of ac- quired habits, 41; criticises Spen- cer's 1st and 3d form in evidence of proof of acquired characters, 43-44; supports Darwin's theory of sexual selection, 88; criticises Wal- lace's ideas on sexual selection, 92-93; on aesthetic taste of animals, 97-98; on species, lOG-107; on phys- natural iological selection, 110-112; opposes selection as originator of species, 113-115; reply to Meldola, 115-116; reply to Galton, 115; phys- iological selection opposed by Wallace. 116-117; reply to Wallace's criticism on physiological selec- tion, 118-119; controversy with Dyer, 123-124. Rostrhamus 267 Ryder, theory of heredity opposed to Weismann, 17; on inheritance of ac- quired characters, 19; experiments on Japanese goldfish recorded by, 34. Salpinctes 236 Sandpipers 202 Sapsucker , 150, 165 yellow-breasted 154 Sauermann, experiments on the influ- ence of food on color 227 Saxicola 335 ienanthe 187 Sayornis 215 aquaticus 243 nigricans 147, 148, 152, 243 Schurmann, natural selection not cre- ative, 51; discussion of origin of variations, 63. Scolecophagus 146. 218,236, 295 carolinus, acraptotic feathers of . . . 136 Scotiaptex cinereum lappooicum 152 Scops asio 243 Seebohm, criticism of physiological selection, 120-123; glacial epoch as a factor in isolation, 249. 8eedeat«rs 3l2 Segregation, definition of environal, industrial, austentational, defen- sive, nidificational, chronal, cycli- cal, seasonal, spatial, geographi- cal, local, migrational, transporta- tional, geological, fertilizational, artifical, reflexive, conjugational, social, sexual, germinal, floral, im- pregnational, 128-130; institution- al, intensive, 131. Segregation of the fit, 116, 120; objec- tions to, by Dyer, 123. Segregation, potential and prepoten- tional 130 Seiurus 216 217, 328 aurocapillus 187, 328 noveboracensis 328 Sematic colors, definition of 194, 200 Setophaga 330 miniata 330 picta, distribution of black on. 147. 148 ruticilla, distribution of black on, 147-148; instance of correlative colors. 156, 221. Sexual Coloration, Beddard on 89, 90 Sexual intensification, explanation of. 68, 69 Sexual recognition, law of 209 Sexual selection, Darwin on, 80; criti- cized by Wallace, 82-83; discussed by Wallace, 85-86; Stolzmaun's view ol, 91; Peckham on, 88; Bed- dard opposed to, 88; Romanes sup- ports theory of, 88; Wallace's objec- tions criticised by Romanes, 92-93; Weismann on, 97; summary of 101, 102. Shrikes 218,317 Sialia 222,229, 236, 336 arctica 158 siilis 213, 222 Sitta 236, 334 canadensis 188 carolinensis 187 Siskin, pine 180 Size, segregate, definition of 180 INDEX. 359 Snow-bunting 136 Snowflake 301 McKay's 302 Socialistic colors, definition of 209 Solitaire 336 Townsencl's 204, 217 Sozuatoplasm, explanation of 11, 12, 13 Sparrow, Bell's 307 black- throated 307 chipping 217. 306 dusky seaside 151 fox 308 Gaicbel's 184 golden-crowned 176, 209 grasshopper 184 Harris's 183 house 209 lark 301 rufous-crowned 307 sage 307 savanna 233, 304 seaside S04 song 248,249, 260, 308 Texas 308 tree 305 vesper 303 white-crowned 209, 306 white- throated 183 western savanna 184 Specialized colors, classification of, 143-146 ; with or without loss of pro- tection, 145, Species, nature of, 103-106; Eomanes on, 106-107. Spencer, theory of physiological units, 6; on simplicity of reproductive cells, 17; three forms of evidence in proof of inheritance of acqxtired characters, 42 ; first and third form in proof of inheritance of acquired characters criticised by Ball and Bomanes, 43-44; discussion of use and disuse, 44-45. Speotyto cuniculariahypogsea.197, 210, 274 Sphyrapicus 236, 244,248, 280 ruber 243, 244 thyroideus 146, 150, 165, 223, 281 varius 164 , 192, 222, 244, 262 nuohalis 244, 245 Spinus 157, 218, 800 lawrencei 177, 222 plnus 145, 180, 215, 299 psaltria 160, 177, 195, 241, 246 arizonie 160,161, 242 mexicana 146, 242 tristis, specialization of without loss of protection i46 Spiza 321 americana 222 Spizella 180, 196, 216, 217, 236, 306 artigularis 306 breweri 254, 306 pallida 254, 306 Sporophila 312 morelletti 146 Squirrel, black headed ground 68 Stejneger on mimicry, 198 ; on albinism and melanism, 226. Stelgidopteryx 315 serripennis 215 Stolzmann, views on sexual selection. . 91 Stone on plumage changes without moult 134 Stonechats 335 StrigidsB 273 Strix 273 Structure, law of, 64; definition of, 77; by Cope, 77 ; segregate, definition of, 130. Sturnella 293 defilippii 166, 240 magna. 156, 167, 175, 178, 182, 203, 211, 239 Successional relation, definition of by Cope 77 Surniculus dicruroides 198 Swallow 314 bank 315 barn 218, 314 cliff 218, 314 rough-winged 315 ■ violet-green 210, 216, 216, 218 white-bellied 315 white-breasted 210, 218 Swifts 283 Sylvania 329 canadensis 221 mitrata 222 pusilla 157, 221 pileolata 243 Sylviidffi 334 Tachycineta 216, 316 bicolor 210, 218 tha lassina 210, 216. 218, 316 Tanager 160, 313 Louisiana 160, 180 scarlet 143,165, 180 summer 152, 222 western 165, 222 Tanagrldas 313 Taxology, successional 164 Teleology, explanation of by Cope 78 Terpsiphone cristata, as instance of plumage change from dark to light without moult 134 360 CALIFORNIA ACADEMY OF SCIENCES. Tetraonidje 257 Tetro 236 Thomson, explanation of anabolism and katabolism, 68; with Geddes places sexual intensification upon firm basis, 73. ThrasEeetus • 270 Thrashers 196, 332 Thrushes, water 328 Thrush, wood 185 varied 186 Thryothorus bewickii 254 ludovicianus 254 Titmice 196 Tits 333 Todd, J. E., on directive colors 201 Towhee 212, 230, 309 California 182, 203 Transmission, abridged or simplified, definition of 80 interrupted or latent, definition of. 79 mutual and amphigonous, defini- tion of 79 •sexual, definition of 79 uninterrupted or continuous, defi- nition of 79 Trochilidffl 284 Trochilus 221. 236 TroglodytidfB 332 Trogon 277 TrogonidBB 277 Turdidse 335 Turdus musteliniis 185 Turkeys 263, 264 Tympanuchus 261 Tyrannidffi 285 TyrannuB 216, 217, 218, 285 crassirostris, instance of correla- tive colors 155 dominicensis, instance of correla- tive colors 155 melancholicua couchii 286 tyrannus 155, 182, 199, 286 verticalis 153, 254,255, 286 vociferans 254, 255 Urubitiaga 270 anthracina 146 Use and disuse, principle first sug- gested by Lamarck, 2; principle ac- cepted by Darwin, 3; explanation of, by Darwin, 25; discussion of, by Spencer, 44-45; criticized by Poul- ton, 47. Vines, an examination of some points in Prof. Weismann's theory of heredity, 11; admits the immortal- ity of protoza, 11; questions ex- planations of evolution of immor- tal protoza into mortal metazoa, 11; criticism of Weismann's theory of heredity, 12; criticism of Weis- mann's theory of continuity of germ-plasm, 13; Weismann's reply to, 15. VlreonidEB 317 Vigor, segregate definition of 131 Vultures, American 267 Vireo 157, 196. 215, 317 atricapillus 221 crassirostris 318 flavescens 318 flavifrons 157 flavoviridis 157 ochraceus 318 Variations, Weismann's theory of, 55, 56; Weismann's theory of, argued against by Hartog, 56-57; explana- tion of, 59-60; explanation of con- servative variations, 61; explana- tion of progressive, 61-62; second- ary laws of, Brooks, 62; Schnr- mann's discussion of the origin of, 63; further discussion of. 71; Gu- lick's criticism of Brooks' theory of, 72. Wag-tail 216, 217, 331 water.. 217 Wallace, criticized on account of argu- ment on v:\riations, 52-53; opposed to Darwin's theory of sexual selec- tion, 82-83 ; criticism of sexual selection opposed by PouUon. 84; on sexual selection, 85-86 ; Ro- manes' objections to his views on sexual selection, 92-93; objections to physiological selection, 116-117; Romanes' reply to criticism, 118- 119; on recognition markings, 200- 201; on geographical distribution, 234. Wax-wings 216, 217, 316 Bohemian 190 cedar 190 Japanese 316 Warbler, Audubon's 219 bay- breasted 185 INDEX. 361 Warbler, black 161 black and white 320 Blackburnlan 148 Brasber's 331 cfenilean 319 golden-winged 321 gray 217 hedge 212 hooded 329 Kentucky 329 Lncy'B 217 magnolia 118, 219 Nashville 217 palm ' 219 parula 324 prothonotary 320 red 157, 330 red-faced 330 Swaiuson's 218, 320 western 136 white 151 wood 319,325 worm-eating, 320 yellow-rumped 158, 182, 203, 219 yellow-throated 215 "Water-ouzel 219 Weismanu, value of his work, 8; on death, 8; immortality of protozoa, 9; against existence of neucleo- plasm as advocated by Naegeli, 10; reply to the objections of Vines, 13; on embryogenesis, 16; theory of heredity opposed by Ryder, 17; summary of arguments between Weismann and opponents, 21; ex- planation of pammixis, 22, on trans- mission of mutilations, 30; experi- ments on tails of white mice, 31 ; criticism of observations on feet of Chinese ladies by Cunningham, 31: inheritance of artificially induced epilepsy in guinea pigs, 33-34; theory of variation, 55 56; theory of variation criticized by Hartog, 56-57: on sexual selection, 97. Whip-poor-wills 196, 207 Woodpecker 203, 210, 213, 279, 280 Calif oruian . . 143,163,170,173,178, 191 downy 175, 211, 255 golden-fronted 222 hairy 255 red-headed U5, 217 three-toed 156, 222 Williamson's 222 Wrens 196, 332 Wrynecks 279, 280 Xanthocephalns 218, 236 291 xanthocephalus, instance of corre- lation between red and yellow, 155, 157 Xanthoura luxuosa 158, 243 guatemalenais 243 Xenopicus 224, 280 albolarvatus 146, 281 Yarrell, on changes of plumage. .132, 133, 136 Zenaidura macroura 205 Zouotrichia 180, 196, 305 albicollis 183, 305 coronata 187. 176, 209, 305 leucophrys 209, 254, 3U5 gambeli 184, 254 querula 183, 305 Zoorubin 138 PLATE I ^.„ ! < )# 6 i |,,g 8 /.«i II del. C.A.K. 5 '^j-' '1 9 ■"°^: ■ '^^ 10 4 12 PLATE II. Melanerpes formicivorusbairdi Sphyrapicus vanus 14 15 Sphyrapicus thyroides rin!. C * 1^ '«%■' l-^t> ' I e" I rev iter, PLATE ill. PLATE IV. PLATE V. Xanthocephalus xanthocephalus Agelaius L 1 r Icterus cucullaius Habia melanocephala Habia ludoviciana Colaptes auratus Colaptes cafer Piranga ludoviciana Pirangaerythromelas Re^ulus satrapa Re^ulus calendula Icierus cucullatusnelsoni Setophaga ruticilla ? Setopha§a ruticillac? Sphyrapicus varius Sphyrapicus varius Agelaius phoeniceusjuv.t? A^elaius phceniceus ad.d* del.C.A.K. UT-H.tiRIT~ON « Pc; PLATE VI. Throat i Myiarchus cinerascens Myiarchus mexicanys Myiarchus crinitus Icterus cucullatus nelsoni C- '-* K UtL PLATE VII. Spinas psaliria Spinus psaltria an'zonae Spinus psaltria mexicana IJ-TH BfllTTCH 8. TREY £ F. C.A. K. DEL. PLATE VIII. (0 c a E ^^m'^^>».f>\-''^\^^ y M'^- 1 -an 0) E (0 U "a. , z", '"-■ ui a E o >>. I. « del. C.A.K. PLATE IX . PIPI LO. PLATE X. x; 7 ^'f?x SJ:> \6 )_ \^ r\ {t"\ / \5 1 vC I 1 •^ W ^^ ,--r Megascops asio. Cyanocitta. PLATE XI. DRYOBATES SCALARIS NUTTALI & BOREALIS. PLATE XII. Chordeiues. 1 Melospiza Pasciata 2 cinerea 3 fasciatd rufina 4 guttata 5 6 7 8 samuelis heermanni Fallax montana del.C.AK., ■Y.SF PLATE XIII. PLATE XIV. A^elaius phoeniceus J* A^elaius ^ubernalor J" Agelaius tricolor c? A|elaius phceniceus (? A^elaius ^ubernator^ winter summer Agelaius tricolor^ summer A^elaius ^ubernator ^ winter MC.A.K. .■;-■■''. e PIT rj;/ .t rffr- ■ ^. ** PLATE XV. I Sphyrapicus varius juv. 4 2 ■■ ' ^ ad. winter 3 •■ •• ? ad. breeding 4 " nuchalis?ail. 5 ■ cJ* ad. G " nuchalis(?ad. 7 ruberd*ad. del.C.A.K. in.tJH'im'i'v iW-X S.F. PLATE XVI. Icterus cucullalu5 nelsoni Icterus cucullatus nelsoni Icterus bullocki Icterus ^albula Icterus bullocki Icterus spur! us C.A K. OEL^ PLATE XVII. Icterus cucullatus Icterus cucullatus nelsoni Icterus parisorum Icterus spun US C A. ,'f. DEL Dendroica caerulea pensylvanica f M/(^l f> castanea ! ■, I % I' H 9, % Striata blackburniffi % "^i^-MM dominica gracias ni^rescens chrysoparia virens bwnsendi occidental is ill "Jf^Wi kirtlandi I vi|orsii palmarum discolor »f Ml *-.. .; ^v.-« aiitf PLATE XVIll. Coverts Throat Breast Sides Abdomen UnderTail Coverts * * ,M '■ m M^ ■^i^^r P^5 IHHHJi » '"'* .■' M «' t. ,, t)* i> ^ »' HUl.S mil i HH 1 ^.>i 51 ^uL ■ 1 u % i|i|* ,f* '•% 4 k'i « « tl#^^'/^ /" A .III II III A'* V h III! 1 ^SS^^^i£Mi ' -. *:;.:.' . v:-::'.^>i Dendroica Topof Heac 1 Back Rump UpperTail Coverts Ear tigrina : '^ fcLiiiMi A H*i« £■. olivacea wiisis P ^r-' :. .:::r>:i ■■ aestiva • .' \ ■' -K. . bryanti ■ ■ - ? .^.,.-- .-.,^ caerulescens :-^.€..i^L -yx corona ta lll^fl 1 ii|TfTii auduboni fZ\ ;^#JJL i^TTfi;...,^ maculosa ^^ caerulea YM^'^ |, -J ., r^g. ■■■■-"■ '■''■■.'.■- ;. -■ . ..vi VN PLATE XIX. ir Coverts Throat Breast Sides Abdomen UnderTail Coverts -*?*■#'■' T'"' ;V-,V, imiii mm} LJH nrf u W !U ' C j * ' , 1 : t f ' ^H HFrffw 1 riM>^/;f 1 %w^w ff '/ » f i i' .'It „ -. > // 1 1. r 11 1 WW ^^^1^ ^^1 ^^^iL A \\l\\\ mui r 1 4( >i miu ^^^pxi^^m , miH mm ^H ,;.::;;.. :;| mm ^H V ' ' -^ 1 1 JkM^ Ulit^ J^. wm /•','^ J '*'- ,. _ -1, M4 ** U V i* *, :'!^^« ■:3>3 >» tao ;2Pi: _>■•>- ■■;■ Sai8l ^-^iZ>S»!.5b3^^ a> :;3>jr>'i(a,' /<^^ '^y-'-^L^A' J ,: R-^ V>_>[ ■rP'i>'y_7J^ ■ "O ^> SMiiPf^ ,'1 j^ ■'"^3lh"i^ : ;'~> "-<' "^i^-'' f> j3l^ -• ..> " v^, ■;>£» >'~?> 33S>i" '^'"S '^ .,-t^O '^'-2!^^^- ""> '■'» -}j i>' '5^i>' "^ "i '.'' 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