Chap. 34 



AMPHIBIANS 



685 



Fig. 34.4. Tiger salamander {Ambystoma tigrinum) . 1, adult and 2, larva, 

 adult 7 inches long. Under particular conditions and in certain parts of the 

 country the larva (axolotl) grows to full size and sexual maturity without trans- 

 forming. 



red spots along the sides, the adult coloration. These are the animals that will 

 reproduce the next spring. In some parts of their range, certain ponds on Long 

 Island and Cape Cod, spotted newts retain their gills and do not leave the 

 water for a long time, if at all. If such newts are kept in cages, with little water 

 except that in damp moss, their gills shrink away and their skin changes in 

 texture to the land type. This is an example of the easy adjustment of which 

 amphibians are capable. 



Order Anura — Frogs and Toads 



Frogs and toads hop and leap with an always ready kick-off by the mas- 

 sive muscles of the thighs and calves that snap the bent hindlegs into ac- 

 tion. When salamanders walk, their body muscles work, pull and swing the 

 body. When frogs hop, the leg muscles work, but the weak body muscles take 

 little part. Frogs have the shortest backs and smallest number of presacral 

 vertebrae of any land-living vertebrate. Correlating with this they have very 

 long hip bones (ilia) extended to meet the fanlike extensions of the sacral 

 vertebra. The meeting place is the conspicuous hump on a frog's back, the 

 outward sign of a peculiar evolution. 



Frogs and toads are more specialized than salamanders. Their metamor- 

 phosis includes not only the change from gills to lungs, but from the digestive 

 tube of a herbivore to that of a carnivore, and from a mouth fitted for scraping 



