A quatic A mphibians 209 



likewise drop when they have become 

 proficient swimmers and are old enough 

 to procure food. 



A small frog (Phrynixalus) spends its 

 nursery days enclosed in a transparent 

 sausage-shaped membrane which is aban- 

 doned in mountain streams. 



In Dendrobates, a small South American 

 frog living in districts where the pools 

 may dry up in a few days, the parents 

 carry the tadpoles on their backs, the 

 offspring adhering by their large sucker- 

 like lips. The young are thus carried 

 from one pool to another. 



The more animal food the tadpoles 

 obtain the quicker they develop. The 

 tadpole stage may persist in fact in most 

 frogs and toads for nine months or more 

 if the animals are fed on vegetable matter 

 only. Experiments have proved that if 

 tadpoles are kept under water con- 

 tinuously by placing a sheet of perforated 

 zinc between them and the surface of 



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