14 STEUCTURE AND CLASSIFICATION OF BIRDS 



derived from an examination of other structures ; for 

 while Phalacrocorax is quite accipitrine the other Stega- 

 nopodes are quite different. Herons agree with the 

 Accipitres, while the ciconiine pattern leads towards that 

 of the Tubinares, and is identical in some cases with that of 

 the American vultures. The cuckoos should be, when 

 judged by the feathering of their wings, placed in the 

 immediate neighbourhood of the Columbse, from which group 

 Goura ought to be separated. Chauna is practically a 

 pigeon in these characters, while the Limicolse are not far 

 off. The Crypturi are gallinaceous.^ 



Pterylosis 



As a general rule the feathers of birds are not distribubed 

 uniformly over the surface of the body, but are set in the 

 skin in definite tracts, between which are spaces that are 

 entirely bare or covered only with down plumage. The 

 feathered tracts are termed pterylae, the interspaces apteria. 

 A few birds, such as the struthious, the penguins, and th« 

 screamers, have an uninterrupted plumage ; but this state 

 of affairs, though corresponding with what one supposes 

 to be the original condition, is not necessarily so in the 

 birds under consideration. Thus, although the ostrich has 

 an uninterrupted plumage in the adult state, the young 

 embryo, as first figured by Miss Lindsay, has definite 

 pterylae, thus proving that the continuous feathering is here 

 purely secondary. There is a ' very great variety in the 

 arrangement of the pterylae among birds, and for the details 



1 De Meijeke has devoted some pains to the arrangement of the feathers 

 ■with reference to each other, a subject which, as he says, has been hitherto 

 treated of only in a stepmotherly fashion. It appears from his investigations 

 that the feathers are arranged in groups, as are the hairs of mammals. For 

 example, upon the naked region of the head of Numida the feathers are 

 grouped in fours, a stronger feather with two hair-like feathers, one on one side 

 and one on the other. This is what is generally found, a central stronger 

 feather with hair feathers surrounding it. There is here a remarkable analogy 

 with the grouping of mammalian hairs, where a stronger hair is often sur- 

 rounded by three or four more slender hairs. Moseley also in the case of the 

 dodo (q.v.) has found the feathers to be grouped in threes. 



