YOUNG BIRDS AND RECORDS OF THE PAST 153 



marks the pause, or rather slowing down of growth, 

 which followed the completion of the protoptyle. 



The nestling down of penguins and petrels admirably 

 displays these phenomena ; but they are no less distinct 

 in the nestling down of the young barn owl, which, 

 obviously, differs in a very striking manner from that of 

 the tawny owl, for example, wherein, as we have seen, the 

 mesoptyle down is of a complex character; and this com- 

 plexity is found to far greater perfection in young mega- 

 podes and young tinamous, wherein the mesoptyle feathers 

 have hitherto been mistaken for contour feathers. The 

 mesoptyle nestling down feathers of many gallinaceous 

 birds, and of the swans, geese, and ducks hold a half-way 

 position : being more degenerate than those of the tawny 

 owl, but far less so than in, say, the young barn owl ; 

 and this because they display a long shaft bearing a 

 double row of barbs. But the barbs are of a degenerate 

 character. In the gallinaceous birds every possible degree 

 in the degradation of the mesoptyle is to be met with. 

 In the young turkey, for instance, it is relatively well 

 developed, presenting a long shaft and an aftershaft ; in 

 the young grouse the shaft has disappeared, and the 

 down is umbelliform, though far less degenerate than is 

 the young owl or hawk. 



In all contour feathers save the remiges or quill-feathers 

 and rectrices or tail-feathers, there will be found at the 

 base of the shaft a second smaller shaft bearing a vane 

 of its own, and rather " downy " in texture. This 

 is known as the aftershaft. In the gaUinaceous birds 

 it is very large, in the owls it is absent ; between the two 

 every gradation in degeneration will be found. But 

 nowhere, among adult birds, will so large an aftershaft 

 be found as in the emus and cassowaries, in which, if 



