64 APPLIED BIOLOGY 



bills of Australia ; in some snakes ; in some salamanders ; 

 in some fishes ; in some insects ; and in other kinds of lower 

 animals. 



There is a great advantage in viviparous over oviparous 

 development in the protection afforded the eggs and em- 

 bryos. Hence relatively few eggs need be produced. It is 

 well known that many fishes and other oviparous animals 

 produce an astounding number of eggs, and that vast numbers 

 of the eggs and young are destroyed. Sharks illustrate 

 the advantage of viviparous development for fishes. Few 

 eggs are formed, and these are retained in the oviducts, 

 not only until the young animals are fully formed, but foi; 

 many months, until they have grown to be several inches 

 long. They are then born (expelled by muscular contraction 

 of the oviducts), and are well able to shift for themselves. 

 Thus a few sharks' eggs well protected during development 

 will perpetuate the species as successfully as would hundreds 

 of eggs forced to develop oviparously and exposed to attacks 

 of numerous enemies. 



A similar case is found among salamanders, which are 

 near relatives of the frogs and toads. Our common 

 salamanders lay each spring large masses of eggs. In a 

 species which lives in the mountains in Europe, each female 

 forms but two eggs in a year, and these are retained in the 

 oviducts until developed into young salamanders ready to 

 care for themselves. 



RELATION OF FROG TO OTHER ANIMALS: CLASSIFI- 

 CATION 



64. Classification of the Frog. By this phrase is meant 

 the position of the frog in the scientific list of the animals 

 of the animal kingdom. In a dictionary or encyclopedia 

 we find frogs placed according to alphabetical order, but in 

 a book of zoology they are grouped with the other animals 



