CHAPTER XXDC 

 THE AMPHIBIA, LIFE HISTORY AND HABITS 



Vocabulary 



Caudal, pertaining to the tail. 



Cellular, composed of cells. 



Obscured, hidden. 



Hibernate, to remain inactive over winter. 



Eject, throw out. 



Vicissitudes, changes and accidents of life. 



Life History. The life history of a frog is a true metamorphosis 

 and illustrates perfectly the development of an air-breathing land 

 animal from a gill-using aquatic form. 



The female lays the eggs in the water, early in the spring, and 

 they are fertilized immediately, thus assuring more certain develop- 

 ment than in the case of fish. Each egg is surrounded by a jelly- 

 like coat which swells in the water until all are joined in a gelatinous 

 mass. In this, dark-colored eggs about as large as peas can be 

 seen, each surrounded by a transparent covering. The rate of 

 embryo growth depends somewhat upon temperature and food 

 conditions but usually the parts can be distinguished within each 

 egg in less than ten days. The little tadpoles themselves leave 

 the mass within two weeks. 



At this stage they fasten themselves to stones by means of 

 sucking discs and live by absorbing the attached egg yolk, no 

 mouth being developed. There are three external gills, a narrow 

 fish-like body, well developed, and a caudal fin. 



Next they become free swimmers. The mouth now appears, 

 and a very long coiled digestive tract begins work on the vegetable 

 scums which are their food. Gradually a fold of skin grows back- 

 ward over the gills, like an operculum, leaving only a small opening 



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