92 GENERAL ORNITHOLOGY. 



parts where the new ones grow. A few birds, as Ptarmigan (Lagopus), regularly have a third 

 or triple moult, '' shedding their feathers as usual by annual moult iu summer, then soon chang- 

 ing by another (partial) moult to pure white for the winter, then in spring moulting again more 

 or less to assume their wedding dress." As a rule, feathers are moulted so gradually, particu- 

 larly those of wings and tail, and so simultaneously upon right and left sides of the body, that 

 birds are at no time deprived of power of flight : moreover, the first flight-feathers acquired by 

 youug birds are usually kept till the next season. But those that fly very early, before they 

 are half grown, as so many gallinaceous birds do, include their first weak wing-feathers in the 

 general moult which occurs to young and old in autumn. The Duck family (Anatidcc) and 

 some others ofier the remarkable case, that they drop their wing-quills so nearly all at once as 

 to be for some time deprived of power of flight ; and on regaining them the males acquire a 

 postnuptial plumage very difierent from that gay attire they last wore — a dingy dress like that 

 of the female. Numberless other birds, like our Tanagers, the males of which are brilliant in 

 breeding dress, moult into a postnuptial plumage in which they resemble their homely mates. 

 It is difficult to lay down any rules of moulting for particular groups of birds, since very closely 

 related species may diflFer greatly in respect to their changes of plumage, and the subject has 

 not yet received the attention its interest and importance should claim for it. 



The physiological processes involved in endysis and ecdysis are analogous to those con- 

 cerned in shedding of hair of mammals, casting of cuticle of reptiles ; for hair, cuticle, and 

 feather are alike cuticular or epidermal structures, as we have seen (p. 81). Therefore it 

 need surprise no one to learn that feathers are not the only tegumentary appendages subject to 

 moult. Some birds shed portions of the horny covering of the bill, feet, claws, even eyelids. 

 Thus in the Grouse family (Tetraonidce) the greatly overgrown claws of some species in the 

 winter season are reduced in size by moult or by mechanical wearing away (as is also the 

 case with some Lemmings among mammals) ; and some Grouse develop along the sides of 

 the toes a fringe of horny process which is regularly shed and renewed. The bill of Redpolls 

 of the genus ^giothus enlarges in summer, bulging out into a redundant growth of horn, which 

 in winter is mechanically worn down till the bill resumes its usual acutely conical shape. Our 

 White Pelican regularly sheds a curious horny outgrowth of the upper mandible. But the most 

 remarkable known cases of such ecdysis of horn are found in various species of the Auk family 

 (Alcidce) ; for a full account of which the reader is referred to my article in the body of this 

 book, where that family is treated at length. 



Aptosochromatism. — It is certain that many birds change the colors of their plumage 

 without losing or gaining any feathers, and thus independently of moult. This is what I call 

 aptosochromatism (Gr. a, privative ; nrSxris, ptosis, a falling off or away ; xP^H'^j chroma, color, 

 complexion). Though I coined this word many years ago, and some of the facts to which it 

 applies were known long before my time, certain writers have had the hardihood to deny the 

 facts and decry the term. It is asserted by such persons that a feather becomes a dry dead ap- 

 pendage as soon as it attains its growth ; which is not true. A feather, like a hair or a claw, 

 retains vitality for a time after it, ceases to grow ; and does not die until it is ready to be cast 

 like a foreign body. True, there is no blood circulation after the pin-feather stage is past, and 

 the " soul " of the feather has turned to dry pith ; but a certain degree of vascularity persists for 

 some time thereafter, maintaining vital connection with the body, and permitting certain molec- 

 ular changes of pigmentation in the substance of the feather. The full-grown hairs of a mam- 

 mal long retain a sort of circulation which in some cases is capable of altering their color ; 

 witness the bleacliing of black or brown human hair in a few hours under some strong mental 

 emotions of grief or terror. Feathers are in precisely the same case. Nay, more ; a different 

 degree of vitality can easily be shown to persist in different parts of the same feather. Thus, 

 the primaries of many Gulls acquire definite white tips ; and these wear away sooner than the 



