208 



THE FROG 



CHAP. 



on the left side the spout-like aperture remains open for 

 some time longer, and the water from both sides passes 

 out through it (D). All this time the tadpole is to all 

 intents and purposes a fish ; apart from the possession 



FIG. 66. Stages in the later development of the Tadpole, (x 7|.) 

 A, stage with external gills ; B, stage showing the formation of the operculum ; 

 C, later stage, in which the external gills are disappearing ; D, stage with in- 

 ternal gills and budding limbs ; D 1 , dissection of same stage to show the heart, 

 gills, and lungs. E, later stage, in which the limbs are further differentiated. 

 (After Howes.) 



of gills and a tail-fin, in the structure of the circulatory 

 organs and various other parts it is more like a fish 

 than a frog. 



The lungs (D 1 ) become functional, and the tadpole is 

 now truly amphibious, rising periodically to the surface, 

 to breathe air. At a later stage, however, the gills 



