126 INTRODUCTION TO THE CLASS OF AMPHIBIANS 



cation, and by the latest authorities the term Am-pJiib'i-a 

 has been adopted instead. 



In the transition from the water-habiting Fishes, with 

 gills and fins, to the land-going Reptiles, with lungs and legs, 

 Nature has made some strange combinations. In some in- 

 stances fins, legs, lungs and gills have become so mixed that 

 several notable misfits have resulted. In some cases we see 

 legs going with gills, and in others fins and lungs are associ- 

 ated. Many of the Amphibians will serve teachers as very 

 striking object lessons in the evolution of animal forms. 



The Class Amphibia contains the cold-blooded verte- 

 brates known as frogs, toads, salamanders, newts, proteans 

 and sirens. 



In the insect world we are familiar with the three stages 

 of existence by which the larva passes into the chrysalis stage, 

 and later on emerges as a perfect insect. Here, among the 

 vertebrates, we find creatures which also pass through two 

 very distinct and sharply defined stages. 



An Amphibian, if literally translated from the Greek, is a 

 creature of "two lives." A typical amphibian begins life as 

 a legless, fish-like creature, possessed of perfect gills, an eel- 

 like tail, and living wholly in water. This is the larval stage 

 of the animal. Later on, four legs make their appearance, the 

 tail disappears by absorption into the body, the digestive 

 organs change from simple to complex form and lungs take 

 the place of gills. In this adult stage the creature (usually) 

 is fitted for life on land if it so elects. 



Owing to the bewildering variations of form and anatomy 

 that are exhibited by various species, it is almost impossible 



