Chap. 34 AMPHIBIANS 687 



algae to one adapted to catching insects. They also change from fishlike swim- 

 mers to expert jumpers. A description of the essentials of the biology of frogs 

 is included later in this chapter. 



Order Apoda — Caecilians 



At first glance caecilians might be mistaken for earthworms instead of verte- 

 brates. Except for a few that are aquatic, they live underground, burrowing in 

 moist places in Mexico, South America, and other tropical countries. Their 

 amphibian characteristics are unmistakable. They have gilled larvae and go 

 through the typical metamorphosis. The adults have well-developed lungs and 

 their skin is smooth and glandular. 



The Frog — An Example of the Vertebrates 



Frogs are nature's gift to laboratory study and experiment. They are abun- 

 dant, widely distributed, and live well in captivity. Hundreds of papers and 

 books have been written about them and important facts have been discovered 

 by means of them. The frogs most frequently used are: the leopard frog, Rana 

 pipiens (Fig. 34.6), distributed from the east coast through the western states 

 except California; and the bullfrog, Rana catesbiana, the largest North Amer- 

 ican species, with a natural range through the eastern half of the United States 

 and an introduced range in the west. 



Ecology and Life History. Frogs are limited to lands where there is enough 

 moisture. They do not live in deserts, in frigid climates, or salt water. In tem- 

 perate climates, they commonly leave the water after their spring breeding 



Fig. 34.6. Leopard frog. Rana pipiens. the frog of the laboratories. It is also 

 the mainstay of the edible frog business that supplies hotels and markets for 

 which an average expert can dress 1000 frogs per hour. 



