Chap. 34 AMPHIBIANS 689 



Frogs have little or no defense against predators. Diving beetles suck out the 

 body juices of the tadpoles and catfishes swallow a hundred of them at a gulp. 

 Turtles, snakes, herons, raccoons, and man all prey upon them. They are used 

 in hotels, markets, and laboratories, a total that goes into billions per year, 

 chiefly leopard frogs. 



Parasites and Diseases. Leeches clamp to their bodies and suck out their 

 blood; molds and bacteria invade their moist skin; flukes, roundworms, and 

 protozoans flourish within their bodies. One of the worst calamities is their 

 wholesale destruction due to the drying out of swamp lands by dams and 

 irrigation. 



Seasonal Life (Fig. 34.8). Frogs and toads are like rabbits: in front they 

 stand; behind, they sit in continual readiness for a take-off. In the ponds, frogs 

 lounge with their nostrils, valves open, just above the surface. The hippo- 

 potamus, also semi-aquatic, does the same thing. In winter, when they are 

 under water they depend upon skin breathing and the lungs are nearly emptied 

 of air. This is adequate for long periods when the metabolism of the body is 

 low and the demand for oxygen decreased. 



In temperate climates, frogs spend the winter in damp protected places, 

 mainly in the muddy bottoms of ponds and in swamps. About mid-winter, 

 preparation for the early breeding period begins in the reproductive organs, 

 supported by food stored in the fat bodies. As spring approaches, the former 

 increase in size and maturity. Secondary sex characters, the horny thumb pads 

 of the males and the vocal sacs, are prominent during the breeding season. At 

 its height, even the most solitary frogs become social as they gather in the 

 ponds in full croak. The male leopard frog and to a lesser degree the female 

 inflate the vocal sacs, one over each shoulder, swelling them larger and larger 

 by drawing air across the vocal cords as the croak is repeated. Then the air is 

 suddenly drawn into the lungs and the sacs collapse. The breeding season 

 reaches its climax in mating, and the release and fertilization of the eggs. A 

 leopard frog produces up to 5000 eggs per season deposited in the water in 

 masses of about 500 each. 



After the breeding period, great changes take place in these frogs that for 

 months have taken no food and for weeks have been congregated in their an- 

 cestral home in water. Promptly they leave the ponds and scatter, each a soli- 

 tary land animal. This is the beginning of the summer-feeding period when fat 

 is accumulated in the fat bodies and glycogen is stored in the liver and muscles. 

 With the chill nights of autumn they stop feeding, and seek winter quarters in 

 the swamps, crowded together by dozens, even hundreds. For the second 

 period of the year they are social animals, urged by sex at one time and by 

 cold weather at the other. 



Life History. For the development of the embryo, and the transformation 

 of the tadpole into the frog, see Figure 34.8 and Chapter 19. 



