A CHAPTER IN DARWINISM 



19 



The frog's egg first gives rise to a little aquatic 

 creature with external gills and a tail the tadpole 

 which gradually loses its gills and its tail and acquires 

 in their place lungs and four legs (Fig. 2), so as now 



FIG. 2. Tadpoles and young of the Common Frog. 1, Eecently hatched (twice 

 natural size) ; 2 and 2a, same enlarged to show the external gills ; 3 and 4, 

 later stages with gill-slits covered by a membrane leaving only the spiracle 

 (see Fig. 16) as an exit for the respired water ; 5, with hind legs appearing ; 

 6, with both fore and hind legs ; 7, atrophy of the tail ; 8, young frog. 



to be fitted for life on dry land. From what we other- 

 wise know of the structure of the frog and the animals 

 to which it is allied, we are justified in concluding that 

 the tadpole is a recapitulative phase of development, 



