YOUNG BIRDS AND RECORDS OF THE PAST 155 



Now what is the meaning of these early feather genera- 

 tions — the protoptyles and mesoptyles ? All the evidence 

 seems to show conclusively that they answer to ancestral 

 plumages ; and if we may judge by what obtains in some 

 of the tinamous, the megapodes, and the tawny owl, for 

 example, and the sequence of plumages in later stages, 

 already discussed in our chapter on coloration, it is by 

 their successive development and decline that new phases 

 of plumage, that is to say of coloration, are developed. 

 In other words, as old, ancestral phases are shed, making 

 their last appearance in the young, new ones are developed 

 by the adults : thus what are the acquirements of the birds 

 of to-day will be the characteristic features of the nestlings 

 to-morrow. 



The gradual degeneration, and in many cases even 

 the suppression, of the nestling down of the helpless or 

 nidicolous types has possibly a special significance. In 

 the young of the lyre bird alone have I found evidence of 

 two generations — ^proto- and mesoptyle — and we may 

 perhaps conclude that in all the other species the mesoptyle 

 alone remains, weak and sparse in most, and suppressed 

 altogether in many. This process of degeneration we may 

 regard as the direct result of the nidicolous condition. 

 Young birds crowded together in a nest keep one another 

 warm when they are not brooded by the mother, and 

 the fact that no down is ever developed on the under 

 surface of the body in such nestlings goes far to confirm 

 this view. 



Surely this story of the nestling down is one of the 

 most striking, one of the most interesting of all the things 

 that the nestling bird has yet revealed to us. As an 

 object-lesson in evolution it would be hard to beat. 



