208 



THE FROG 



pharynx passes is much reduced. After some time, a com- 

 plete union of the operculum with the flank takes place on 

 the right side, the opercular aperture becoming closed : on the 

 left side the spout-like aperture remains open for some time 



FIG. 66. Stages in the later development of the tadpole. 

 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- 

 j 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.) 



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 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. 



