308 



INEZ WHIPPLE WILDER. 



and finally the gills entirely disappear, a process involving the 

 final closure of the gill slits. 



4. The whole gill region becomes shorter and narrower, the 

 latter change being due in part to the flattening down of the 

 prominent bulging supra-branchial regions so that this portion 

 of the head is no longer the widest one. 



df 



a 



FIG. 16. Cross sections at the level of the loth vertebra posterior to the cloaca 

 showing (a) the typical aquatic larval form of tail with the dorsal (df), and the 

 beginning of the ventral (vf) fin fold; (b) the change of form at the approach of 

 metamorphosis. Note that (b) is cut slightly obliquely. Drawn with Abbe 

 camera. X 60. 



5. Further striking changes in the appearance of the head are 

 due to the development of eyelids (eyl, Fig. 17) and of glandular 

 masses in the orbit ventral to the eye, so that the eye and its 

 surroundings come to possess the bulging appearance which is 

 so characteristic an adult feature. 



