CLASS AMPHIBIA 479 



lungs and mouth over the vocal cords, causmg them to vibrate. 

 Vocal sacs, when present usually lying either in the floor or at each 

 corner of the mouth, puff out to make resonating chambers which 

 increase the volume of the call. Bullfrogs quite often call while 

 under water. A few frogs, such as Ascaphus, which lives in the cold 

 mountain streams of Washington and the northwestern United 

 States, have given up their voice and reduced their lungs. Appar- 

 ently voice would not be as useful to this species as to frogs living 

 in quieter places, for its sound would not carry above the noise of 

 the mountain streams. So far as is known, none of the salamanders 

 use voice in attracting mates, and most of them are silent through- 

 out their existence. 



Breeding and Egg-Laying Habits. — Frogs, toads, and salamanders 

 make periodic migrations to ponds and streams for the purpose of 

 egg-laying. These periods, called the breeding season, usually occur 

 during the spring months or, in tropical climates, during the rainy 

 season. Salamanders often come to the pools much earlier than do 

 the frogs and toads and may also begin their egg-laying earlier. 



Most amphibians are oviparous, and their eggs are fertilized by 

 the male after they leave the body of the female. Some salamanders 

 and caecilians, however, have the eggs fertilized before they are 

 laid. Among salamanders in many species, the males deposit sper- 

 matophores containing sperm which are picked up by the females 

 and provide internal fertilization. A few species of salamanders 

 such as the fire salamander of Europe, Salamandra salamandra, give 

 birth to living young. 



While the majority of amphibians lay their eggs in water, and 

 the young pass through tadpole or larval stages, there are many 

 exceptions. The eggs of the Texan cliff frog, Eleutherodactylus 

 latrans, are laid on land, as are the eggs of its relatives in Mexico, 

 and the tadpole stage is passed in the egg. Many salamanders lay 

 their eggs on land. Species in the Southwest, such as Plethodon 

 cinereus, usually lay their eggs in cracks and hollows in logs. The 

 slimy salamander, Plethodon glutinosus, lays its eggs in moist places, 

 often in the walls of caves. Some species of Oriental frogs are 

 reported to lay their eggs in trees high out of the water. There 

 is also reported a South African frog, Arthroleptella lightfooti, which 

 undergoes its entire development on land and cannot swim when 

 placed in water. 



