270 



ANIMAL BIOLOGY 



over the body surface. And soon thereafter the larva, or tadpole, 

 assumes a somewhat fish-like form, with a vertically flattened 

 tail edged by a fin which provides for locomotion during the 

 rest of the animal's purely aquatic life. (Fig. 175.) 



Pronephros 



Oral sucker 



t-"fc.ie*.»ri £dc.&- Harrison • <93l 



Fig. 175. — Development and metamorphosis of the Frog. A, B, stages 

 closely following K in Fig. 174. C-L, stages from egg to adult drawn to scale. 



Independent existence demands sense organs, and these are 

 already functioning in the head region. It also demands the in- 

 take of food which earlier was supplied by the yolk stored in the 

 egg, and so the mouth develops a hard rim for scraping food mate- 



