CLASS AMPHIBIA 



525 



ensues if the heart is frozen. In warm countries many Amphibia 

 seek a moist place of concealment in which to pass the hotter 

 part of the year. They are said to asstivate. 



Poisonous Amphibia. — The poison-glands of the leopard- 

 frog (p. 479) and of the common toad (p. 519) have already been 

 mentioned. Certain salamanders and newts are also provided 

 with poison-glands. The poison acts upon the heart and the 

 central nervous system. It has no effect upon the skin of in- 

 dividuals of the same species, but if inoculated into the blood 

 it poisons even the individual that produces it. As a means of 

 defense the poison is very effective, since an animal that has once 

 felt the effects of an encounter with a poisonous amphibian will 

 not soon repeat the 

 experiment. Some 

 of the most poison- 

 ous species, for ex- 

 ample, Salamandra 

 maculosa, are said 

 to be warningly 

 colored. 



Prehistoric Am- 

 phibia. — Two 

 orders of amphib- 

 ians, the Stego- 

 cephalia and Mi- 

 crosatjria are 

 known only from 

 fossils. The Stego- 

 Cephalia are sala- 

 mander-like extinct 

 animals (Fig. 438) 

 that lived in the 

 Carboniferous, Per- 

 mian, and Triassic periods. They were probably fresh-water 

 or terrestrial creatures. They possessed large, bony dermal 



\#€r 



Fig. 438. — Stegocephalia. Branchiosaurus am- 

 blvstomus. A, skeLton of adult. B, restoration of 

 larva with branchial arches. (From Sedgwick's 

 Zoology, after Credner.) 



