GENERATION, SEX AND ONTOGENY 



237 



an aquatic animal. Soon it is apparent that although the 

 tadpole is steadily and rapidly growing larger, its tail is grow- 

 ing shorter and smaller instead of longer and larger. At the 

 same time, fore and hind legs bud out and rapidly take form 

 and become functional. By the time that the tail gets very 

 short indeed, the young toad is ready to leave the water and 

 live as a land animal. On land the toad lives, as we know, 

 on insects and snails and worms. The metamorphosis of the 

 toad is not so striking as that of the butterfly, but if the tad- 

 pole were inclosed in an unchanging opaque body wall while 

 it was losing its tail and getting its legs, and this wall were 

 to be shed after these changes were made, would not the meta- 

 morphosis be nearly as extraordinary as in the case of the 



FIG. 140. Metamorphosis of the toad: At left, strings of eggs; in water, various tad- 

 pole or larval stages; and on the bank, the adult toads. (Partly after Gage.) 



butterfly? But in the metamorphosis of the toad we can see 

 the gradual and continuous character of the change. 



Many other animals, besides insects and frogs and toads, 

 undergo metamorphosis. The just-hatched sea urchin does 

 not resemble a fully developed sea urchin at all. It is a minute 



