CLASS AMPHIBIA. FROGS, TOADS, SALAMANDERS, AND OTHERS 



399 



Figure 269. Leopard frogs. Dark color phase on 

 the left, and hght color phase on the right. When 

 the animal is in darkness, the hormone intermedin 

 is secreted into the blood stream; the pigment is 

 then dispersed, causing the dark color phase. But 

 when the retina of the eye is stimulated by light, 

 nerve impulses pass to the intermediate lobe of the 

 pituitary gland, causing the production of intermedin 

 to be suppressed, which results in the light color 

 phase. (Photo courtesy of Douglas Eastwood.) 



Regeneration 



The power of regenerating lost parts is 

 remarkably well developed in many Am- 

 phibia. For example, the foot of a two-year- 

 old axolotl was cut off, and in 12 weeks a 

 complete foot was regenerated in its place. 

 The newt (Fig. 270 A) has been observed to 

 regenerate both limbs and tail. The tailless 

 amphibians are apparently unable to regen- 

 erate lost parts to any considerable extent, 

 except in the early stages. As a general rule, 

 the younger tadpoles regenerate limbs or a 

 tail more readily than older specimens. 

 There is a distinct advantage in this posses- 

 sion of the power of regeneration, since am- 

 phibians often escape from their enemies 

 with mutilated limbs or tails; but they are 

 not permanently inconvenienced by the loss, 

 since new parts rapidly grow out. 



Breeding habits 



Most Amphibia are oviparous; and their 

 eggs, as in the leopard frog, are fertilized 

 by the male after extrusion. In some of the 

 tailed forms, however, the eggs are fertilized 

 before they are laid. A few species bring 

 forth their young alive; for example, the al- 

 pine salamander, Saiamaijdra. 



Several curious breeding habits are ex- 

 hibited by certain species. The male obstet- 

 rical toad (Fig. 267), carries the egg strings 

 with him, wound about his hindlimbs; and 

 when the tadpoles are ready to emerge, he 

 takes to the water and allows them to escape. 



The eggs of the Surinam toad (Fig. 267) 

 are placed on the back of the female during 

 copulation, are held there by a sticky secre- 

 tion, and are gradually enveloped by the 

 skin. Within these epidermal pouches, the 

 eggs develop and the tadpole stage is passed; 

 then the young toads escape as air-breathing 

 aquatic animals. 



The American bell toad (Fig. 267) found 

 in California is unique in that fertilization is 

 internal. The male grasps the female around 

 the pelvis, and by use of an external taillike 

 copulatory organ the sperms are deposited 

 in the cloaca of the female. 



The brooding or marsupial tree frogs of 

 Venezuela, Gastrotheca, have a pouch with 

 an opening in the posterior part of the trunk 

 in which the eggs are placed and the young 

 are reared. The female of another species 

 of tree frog carries her eggs in a depression 

 on her back until they are almost ready for 

 metamorphosis. 



Hibernation 



Many amphibians bury themselves in the 

 mud at the bottom of ponds in the autumn 

 and remain there in a dormant condition 

 until the following spring. During this 

 period of hibernation, the vital processes 

 are reduced; no air is taken into the lungs, 

 since all necessary respiration occurs through 

 the skin; no food is eaten, but the physio- 



