loo TYPES OF ANIMAL LIFE 



There are a very large number of species of frogs and 

 toads. At least fourteen kinds inhabit Europe and 

 North Asia and Africa north of the Sahara; above 

 ninety are found in Africa south of the Sahara, some 

 hundred and sixty in the Indian region, more than 

 seventy-five in Australia, no less than three hundred 

 and five in tropical America, and fifty-three in the 

 North American region. 



The phenomena of the life-history of some species of 

 frogs and toads are very curious. The ordinary course 

 of a frog's development takes place thus : The approach 

 of spring calls them forth from their winter retreat, 

 which is generally in mud under water. Great numbers 

 of them are often dug up in the winter time, all clustered 

 together, in the mud at the bottom of a pond. In the 

 month of March their well-known croaking begins to be 

 heard in England, and though itself unmelodious, it 

 possesses a certain charm through its connection Avith 

 the vernal outburst of Nature. It is then that they 

 congregate for egg-laying. Their eggs are little dark, 

 round bodies, enclosed in no solid shell, but only in a 

 thin glutinous envelope. The latter quickly swells in 

 the water, so much so that the " spawn " in the case of 

 the common frog soon comes to have the appearance of 

 a great mass of jelly, through which dark specks (the 

 yolks of the eggs) are scattered. By degrees each little 

 dark mass assumes the form of a young tadpole, which 

 emerges from the egg towaid the end of April. At first 

 it has long filamentary processes of skin projecting from 

 either side of the neck, and these are the primitiv^e gills or 

 aquatic breathing organs. They soon become absorbed 

 and are replaced by other shorter gills, w^iich do not 

 project visibly from the neck. Little by little the limbs 

 bud forth and grow, and at the same time the tail is 



