FIG. 20. STAGES IN THE DEVELOPMENT OF THE FROG. 



i. Embryo from the right side, showing the ventral gland, the hyo 

 cleft and of three gill clefts : a rounded swelling anteriorly marks the s 

 showing the rudiments of the external gills. 3. Larva from the right 

 below, showing the mouth and horny jaws, the ventral gland split int 

 5. From below : the operculum has covered the gills except on the left 

 opercular cavity, and rudiment of hind limb just above the rectum, 

 anus. 8. From the left side, at the commencement of metamorphosis 

 parent operculum, the elbow projecting. 9. Young tailed frog. 



