THE LIFE-HISTORY OF BIRDS 269 



Albatross would appear to retain this covering for nearly as 

 long a period, while the Secretary-bird does not leave the nest 

 till six months old. On the other hand, the Quails and Hemi- 

 podes are fully feathered in about three weeks, while some of the 

 smaller perching birds are sexually mature when six weeks old ! 

 In this procession from the cradle to the grave birds may 

 pa"ss through several phases of plumage. The first of these 

 is downy in texture, and differs in many ways from the later 

 covering of feathers. The precise significance of the downy 

 stage is not easy to grasp. Presumably it represents a some- 

 what degenerate ancestral plumage. In support of this there 

 is evidence to show that the body covering of Archaeopteryx — 

 which must always be taken as the standard in questions of this 

 kind — was of a loose, semiplumous character, only the wing- 

 quills and tail feathers having acquired the characteristic 

 feather-like structure. The absence of these last in nestlings 

 is easily explained by the supposition that development has 

 been retarded for safety's sake until the young birds had 

 acquired the necessary intelligence to fend for themselves, 

 flight being dangerous until then. The young of the Game- 

 birds alone represent such an ancestral stage, and it has already 

 been shown that in them the power of flight at this tender age 

 is a source of danger. But this comparison is not quite exact, 

 since it would appear that the downy covering of the body in 

 these birds really answers to a later plumage. And for this 

 reason : In the Penguins the typical feathers are preceded by 

 two distinct, successive plumages of nestling' down. The first 

 of these barely covers the skin, being almost hair-like in ap- 

 pearance — though microscopically indubitable down feathers — 

 while the second is longer and of a peculiarly " woolly " texture. 

 These last down feathers begin their growth before those of 

 the first plumage have ceased to grow, hence the bases thereof 

 are in direct, organic connection with the tips of the feathers 

 of the second plumage, and in course of time, when these 

 appear through the skin, it is found that each is surmounted 

 by the down feather which preceded it. Similarly, and for 

 the same reason, when; the typical or "definitive" contour 

 feathers appear, they are found to bear upon their tips the 

 down feathers of the second generation. Sometimes all these 

 feathers will be found in direct connection. Among one or 



