Epilogue: What Comes of Studying Vertebrates 



199 



lebe 



Leipzig, 



Fig. 604. Flying fish, Exocoelws volitans. (Courtesy, Breh 

 Bibliographisches Institut.) 



worthy, the fish will literally "drown" if compelled to remain in water. 

 Coming out for an occasional airing is necessary for survival. The ter- 

 restrial locomotion of Anabas is unique. The chief locomotor organs 

 are the gill-covers (opercula), whose edges are spiny. By moving an 

 operculum alternately inward and outward, its spiny edge engaging 

 the substratum, the fish is able to execute an obliquely side wise hitch- 

 ing progress along the beach. Movements of fins and tail may assist. 

 By the same method of progress, it even clambers to a height of 6 feet 

 or more up the rough surface of the trunk of a palm tree. Pursuit of 

 insects as food is the alleged incentive for these aerial excursions. 

 Other notably amphibious fishes are the gobies of the coastal regions 

 of southern Asia and of Africa, which stay out of water for hours during 

 low tide. The "mud goby" (Periophthalmus), a fish about 6 inches long, 

 has short stout pectoral fins by use of which it hops nimbly along the 

 beach foraging for small crustaceans, mollusks, and insects. It is said 

 to leap several inches into the air and, by means of the fins, grasp a 

 mangrove root (exposed at low tide). Having thus gained "foothold" 

 on a mangrove, it may clamber up to a height of 2 or 3 feet (Fig. 605). 



Even the Amphibia can claim an aerial animal, a "flying frog.'* 

 This tropical frog has long digits with webs of skin between them. It 

 makes long sailing leaps, the digits being spread apart so that the 

 webs facilitate gliding through the air. In the evolution of flight, such 

 gliding was probably the initial stage. In reptilian pterosaurs and 

 mammalian bats, webs of skin stretched between digits are an im- 

 portant part of the wing. 



Finally, among Reptilia, chiefly terrestrial animals, are (or were) 

 aquatic ichthyosaurs, plesiosaurs, crocodilians and sea turtles, and 



