396 



METAZOAN PHYLA 



mum of quickness and accuracy in accommodation. Birds possess a 

 nictitating membrane, which is drawn across the eyeball from the inner 

 angle of the eye outward. 



425. Classification. — The classification of birds is a question about 

 which there has been much difference of opinion. All classifications 

 agree, however, in distinguishing between the ancient, reptile-like, 

 fossil birds forming the subclass Archaeornithes (ar ke or' ni thez; G., 



Fig. 271. — Fossil remains of Archaeopteryx siemensi Dames, representing a specimen in the 

 Berlin Museum. {From Steinmann-Doderlein, " Elemente der Palaeontologie.") X /^. 



archaios, ancient, and orni'thes, birds) and represented by a single genus, 

 Archaeopteryx, and a second subclass, the Neornithes (ne or' ni thez; G., 

 neos, new, and ornithes, birds), or modern birds, containing only a few 

 extinct forms. Archaeopteryx (Fig. 271) was a bird about the size of 

 the common crow, had teeth, three free fingers on the wing, flight feathers 

 on the legs, and a long, lizard-like tail (Fig. 272). The caudal vertebrae 

 were separate and the tail had flight feathers on both sides for its full 

 length. The largest living bird is the African ostrich, which is 8 feet in 

 height, but the aepyornis, a bird which lived in Madagascar until about 

 five centuries ago, attained a height of 10 feet. On the other hand, a 



