The Frog. 



83 



vegetable diet; but there is no necessary association of the 

 kind, for the tadpoles of the Cape clawed frog (Xenopus lavis) 

 have an equally watch-spring-like intestine, but feed — chiefly, at 

 any rate — ^upon small crustaceans. The external gills presently 

 shrivel up, and are replaced functionally by the internal gills. 

 At the sides of the pharynx a series of slits appear, which put 

 the interior of the pharynx into communication with the 



Fig- 35 — The young Tadpole of the com- 

 mon Frog {Rana temfioraria), enlarged, 

 showing the external gills. 



Fig. 36. — The under side of the 

 Tadpole of the Frog, showing 

 the coiled digestive tuhe, the 

 suckers (not joined), the in- 

 ternal gills, and the respiratory 

 aperture, enlarged. 



medium in which the animal lives ; these gill-slits, or visceral 

 clefts, become fringed with vascular tags, which are the actual 

 respiratory organs. The intervals between the successive clefts 

 are occupied by cartilaginous bars, the gill-arches, or visceral 

 arches, the function of which is to keep open the clefts, and so 



