GENERATION, SEX AND ONTOGKN\ 



2:^7 



an aquatic animal. Soon it is apparent that altliougli tlie 

 tadj^ole is steadily and ra})idly growinj:; larger, its tail is grow- 

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

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

 and become functional. J^y the time tliat 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 metamorj)hosis of tlie 

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

 pole were inclosed in an unchanging opacpie V)ody 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 crrs; in w.i(cr. VBriou« t*d- 

 pole or larval stages; and on the bank, the adult t.mds. (Partly after Cage.) 



butterfly? But in the metamori^hosis of the toad wc can see 

 the gradual and continuous character of the change. 



Many other animals, besides insects and frogs and toad.-^, 

 undergo metamorphosis. The just-hatched .sea urchin (loes 

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



