300 AMPHIBIA 



Habitat. — As stated before, amphibia hibernate and aestivate. 

 That they are able to live in cavities in solid rock has often been 

 reported. But Buckland, after experiments with frogs and toads 

 enclosed in cavities of stone and excluded from air and food, found 

 that none lived over two years and most succumbed inside of a year. 



Fossil Relatives. — The Stegocephalia are extinct, tailed forms 

 which lived in fresh water. Their teeth were complexly infolding 

 (Labryinthodonts). One form known as Mastodonsaurus had a 

 skull over four feet long and nearly as wide. They were abundant 

 in the lower Permian and Upper Pennsylvanian. Traces of gills in 

 certain fossil forms indicate that the Stegocephalian larvae were 

 aquatic. They were armored, some of them having overlapping 

 scales like fishes. 



The Urodela have very few fossil remains. One, found in Ger- 

 many, in Miocene rocks, was called " homo diluvii testis," or " the 

 man who witnessed the flood." Anuran fossils are rare, and found 

 only from the Comanchian to the present, while Apodan {Gymno- 

 phionan) fossils are unknown. 



The connecting links between the lobe-finned fishes (Cros- 

 sopterygii) and the amphibians have not yet been discovered, but 

 comparison of the skulls, labyrinthine teeth and fishlike shoulder 

 girdles of land-living amphibia with these fishes indicates their close 

 relationship. 



The Stegocephalia are apparently related to certain of the extinct 

 Reptiles, the Theromorpha (Therapsida), which appear to have 

 affinities with the Mammals. Huxley, comparing amphibians with 

 mammals, brought out the fact that both have two occipital condyles, 

 and that the carpal bones resemble each other. But Theromorpha 

 (see page 331) also have two occipital condyles. 



Economic Importance of Amphibia. Positive. — i. As food, we 

 find that frogs (legs) are in considerable demand. 



2. Frogs and toads are important enemies of injurious insects. 



3. As experimental animals for use in Physiology and Embry- 

 ology the Amphibia are unexcelled. 



4. Savages secure arrow poison from the skins of some Anura. 

 Poisonous Amphibians. — The poisons from the skin glands of 



toads, salamanders and newts, when injected can kill mammals, 

 birds, reptiles, and even fishes, provided the dose is proportionate 

 to the size of the animal. Small birds and lizards succumb in a few 

 minutes while guinea-pigs, rabbits and dogs succumb in an hour. 



