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Comparative Morphology of Chordates 



flying pterosaurs. Among Mammalia, chiefly terrestrial, are ceta- 

 ceans, sirenians, seals, and other aquatic animals, flying bats, and 

 such gliders as the "flying" squirrel, "flying" phalanger, and colugo. 



Fig. 605. Gobies, Periophlhalmus. (Courtesy, 

 Brehm: "Tierleben," Leipzig, Bibliographisches 

 Institut.) 



Among Aves are numerous flightless terrestrial birds and many aquatic 

 birds, some of them incapable of flight. 



As one vertebrate Class succeeds another, this radiating pattern of 



Fig. 606. Flying lizard, Draco volans, of the Indo-Malayan region. Like the 

 "flying" squirrel, this lizard is merely a glider. The gliding planes are extensive 

 lateral outfoldings of skin supported by elongated ribs. (After Nicholson. Courtesy, 

 Galloway and Welch: "Text-Book of Zoology," Philadelphia, The Blakiston 

 Company.) 



