o90 ZOOLOGY 



lies in the aqueous humor in front of the entrance of the optic 

 nerve — it has the form of a comlj (whence called pecten) and 

 is dcepl}' pigmented, but its function is quite unknown (Fig. 

 357). 



The class of Birds, or Aves, as they are technicaUy called, 

 is divided into eleven orders as follows : — 



1. The 7'iinning birds : Birds incapable of flight because 

 their wings are rudimentary, e.g. Ostriches. 



2. Tlie swimming bird.s. These are the web-toed birds like 

 the loons, gulls and terns, petrels, pelicans, ducks, geese, and 

 swans. 



.3. The shore birds. These possess long, stilt-like shanks 

 with slight web; such are the flamingoes, herons, storks, 

 cranes, snipes, and plovers. 



4. The ground birds, including the turkeys, grouse, fowl, and 

 quail. 



5. The pigeons, perchers on rocks, with all four toes on the 

 same level. 



6. The birds of prey, with hooked Ijeak and claws (talons), 

 including the vultures, hawks, and o'wls. 



7. The tcdkers, with beak shorter than high, including the 

 parrots, paroquets, etc. 



8. The cuckoos and kingfishers. 



9. The woodpeckers, witli long beaks fitted for drilling into 

 bark. 



10. The long-winged birds, or humming-birds, swifts, and 

 goat-suckers, of varied form, for the humming-birds have 

 slender bills, lint the other groups have short bills and large 

 mouths. The wings are generally long and pointed. 



11. The perchers, including most of the common migratory 

 birds. 



