The Development of the Frog 3 



lower side of the head, by means of which it 

 attaches itself to any solid body that may be in 

 the water. 



As the mouth is being formed, the digestive 

 tract becomes greatly elongated, so that the 

 abdominal region of the body becomes rounded 

 and swollen by the coiled mass of the intestine 

 lying within. Being now provided with horny 

 jaws, the young tadpole feeds actively upon 

 the plants of its habitat, and is, therefore, no 

 longer dependent upon the yolk for growth. 



The gill-clefts make their appearance, at 

 about this time, as four pairs of slit-like open- 

 ings which connect the pharynx with the ex- 

 terior. The edges of these slits become folded 

 to form the internal gills, and as the internal 

 gills increase in size, the external gills gradu- 

 ally diminish and are covered by two folds 

 of skin which grow back over them from in 

 front. These two opercular folds fuse to- 

 gether along the mid-ventral line, and their 

 posterior edges fuse with the body-wall behind 

 the gills, so that the latter are completely en- 

 closed except for a sort of spout on the left 

 side, through which water, taken into the gill- 

 chamber through the mouth, to bathe the gills, 

 passes again to the exterior. 



