94 GENERAL ORNITHOLOGY. 



would not be deciduous, nor drop before the whole feather was ready to fall. While it is not 

 probable, as some have claimed, that a worn feather can mend its ragged edges by a new growth 

 of barbs, barbules, or barbicels, it is certain that a fresh feather retains for a while after it is 

 full grown those molecular movements in its substance which may result in deposition of addi- 

 tional pigment, and in absorption or decomposition of pigment already laid down ; so that some 

 colored areas may be extended or restricted, and also change color to some degree, during the 

 lifetime of an individual feather — that is, without moult — that is, in a word, aptosochromatism. 

 Once more; if we turn from consideraticm of color-change in the webs of feathers to such as 

 may be readily observed in their shafts, we find the same thing again. The surface of a rha- 

 chis is smooth, firm, and solidly horny, quite like the corneous covering of the bill. Now the 

 beak of some birds, as of the genus Leucosticte for example, is black in summer and yellow in 

 winter, and this is aptosochromatism, for nobody imagines that the horny sheath of the bill is 

 shed in this genus; it is an actual alteration in color from black to yellow and back again. 

 The same thing occurs, for instance, in the shaft of a Gull's primary, which alters from blackish 

 to yellowish or white in a certain portion of its extent corresponding to the gradual extension 

 of white areas in the adjoining portions of each web of the same feather, and has nothing what- 

 ever to do with the moult of that feather. The notorious inconstancy of coloration of what are 

 called the " soft parts" of most water birds is another case in point. Such as these are " softer " 

 than feathers, indeed, but horny epidermis is only "soft" in comparison with harder horn, not 

 to the degree of what is commonly called vascularity, for it has no blood vessels. I adduce these 

 facts to bring all the epidermal structures of birds into proper correlation, showing that feathers 

 do not differ from beaks or claws so much as some have assumed in the degree of that kind of 

 vascularity which they retain for a while after they have ceased to grow, and that in the interval 

 between maturity and moult they may continue subject to color-changes (a) by pigmentary 

 vicissitudes, (b) by structural modifications ; both of which modes of alteration in coloration 

 come under the head of aptosochromatism, or change of plumage without loss or gain of any 

 feathers. 



Plumage-changes with Sex, Age, and Season. — Aside from any consideration of the 

 way in which plumage changes, whether by moult or otherwise, the fact remains that most 

 birds of the same species diS"er more or less from one another according to certain circumstances. 

 The dissimilarity is not only in coloration, though this is the usual and most pronounced differ- 

 ence, but also in the degree of development of plumes, — their size, form, and texture. Since 

 young birds are those which have not come to sexual vigor; since breeding recurs at regular 

 periods of adult life, annually or oftener; and since males and females usually differ in plu- 

 mage, — nearly all the various dresses worn by different individuals of the same species are cor- 

 related with conditions of the reproductive system. As the internal generative organs represent 

 of course the essential or primary sexual characters, all those of plumage just indicated may be 

 properly classed as secondary sexual characters. These are of great importance, not only in 

 practical ornithology, but as the basis of some of the soundest views that have been advanced 

 respecting the evolution of specific characters in this class of animals. The generalizations 

 may be made : that when the sexes are strikingly different in plumage, the young at first re- 

 semble the female ; when the adults are alike, the young are diff"erent from either ; when sea- 

 sonal changes are great, the young resemble the fall plumage of the parents ; and, further, that 

 when the adults of two related species of the same genus are nearly alike, the young are usu- 

 ally intermediate, their specific characters not being fully developed. Specific characters are 

 often to be found only in the male, the females of two related species being scarcely distinguish- 

 able, though the males may be told apart at a glance. Extraordinary developments of feathers, 

 as to size, shape, and color, are often confined to one sex, usually the male. The more richly, 

 extensively, or peculiarly tlic male is adorned, the simpler the female in comparison, as the 



