422 



ZOOLOGY 



feathered, to the long-legged Storks and Cranes, in which the distal 

 part of the tibio-tarsus is covered with scales as well as the foot. 

 In aquatic forms a fold of skin or web is stretched between the 

 toes, sometimes including all four digits, as in the Cormorants; 

 sometimes leaving the hallux free, sometimes forming a separate 

 fringe to each digit, as in the Coots and Grebes. As to the toes 

 themselves, the commonest arrangement is for the hallux to be 

 directed backwards, and Nos. 2, 3, and 4, forwards ; but in the Owls 

 No. 4 is reversible, i.e., can be turned in either direction, and 

 in the Parrots, Woodpeckers, &c., it, as well as the hallux, is 

 permanently turned backwards. In the Swifts, on the other hand, 

 all four toes turn forwards. The hallux is frequently vestigial 

 or absent, arid in the Ostrich No. 4 has also atrophied, producing 

 the characteristic two-toed foot of that Bird. 



Pterylosis. With the exception of the Penguins, most Car- 

 inatee have the feathers arranged in distinct feather-tracts or 



cd.pl 



FIG. 1060. A, pterylosis of GypaetUS (Bearded Vulture); B, of Ardea (Heron), al. pt. wing- 

 tract ; c. pt, head-tract ; cd. pt, caudal tract ; cr. pt, crural tract ; cv.apt. cervical apterinm ; 

 hu. pt, humeral tract : Uil. apt, lateral apterium ; p. d. p., p. d. p'. powder-down patches ; sp. pt, 

 spinal tract ; v. apt, ventral apterium ; v. pt, ventral tract. (After Nitsch.) 



pterylse, separated by apteria or featherless spaces. These are 

 commonly much more distinct than in the Pigeon (Fig. 1060), and 

 their form and arrangement are of importance in classification. In 

 the Ratitae, apteria are usually found only in the young, the adult 



