io6 THE INFANCY OF ANIMALS 



the birds this agreement between adult and early post- 

 embryonic stages is conspicuous by its absence. This 

 discrepancy, this lack of agreement, however, is not 

 without its significance. 



When we turn to the later, but still juvenile, stages 

 of growth we find a very close and peculiarly instructive 

 relationship between the coloration of the juvenile and 

 adult stages. Comment has been made already on the 

 fact that no hard-and-fast line can be drawn between 

 embryonic and post-embryonic characters, and the his- 

 tory of the development of antlers indeed shows that 

 neither can we draw a dividing line between young and 

 adult stages. The facts which are now to be reviewed 

 still further demonstrate this overlapping of the juvenile 

 and adult phases of growth. 



To begin with, it is not by any means easy to distinguish 

 between the last of the downy stages of development 

 and that which is marked by the assumption of the first 

 garment of typical contour feathers. But since the 

 determining factor is in this case a structural character, 

 we must return to this point later. 



For the moment, be it noted that the plumage which 

 answers to this first garment — as distinguished from the 

 characteristic downy feathers of the nestling stage — bears 

 a close resemblance to, or may be indistinguishable from 

 that of the adult, in so far as coloration is concerned. The 

 importance of this fact, in the present connection, turns 

 upon the character of the adult plumage, which commonly 

 displays a series of evolutionary phases such as leaves 

 no room for doubt as to the reasonableness of the re- 

 capitulation theory : which has been generally discredited 

 because allowance has not been made for disturbing factors 

 introduced by the necessities of development. 



