132 



GENERAL GROWTH. 



the unsegmented posterior region of the embryo. The hind end 

 of the embryo grows out 

 into a rounded prominence, 

 which rapidly elongates, and 

 becomes a well-marked tail 

 entirely formed by the elon- 

 gation of the post-anal sec- 

 tion of the body. The whole 

 body has a very decided dor- 

 sal flexure, the ventral sur- 

 face being convex. Fig. 78 

 represents an embryo of 

 Bombinator in side view, 

 with the tail commencing to 

 project. The longitudinal 

 section (fig. 76) is taken 

 through an embryo of about 

 the same age. In the cephalic region important changes have 

 taken place. The cranial flexure has become more marked, but 



FIG. 77. EMBRYOS OF THE COMMON FROG. 

 (After Remak.) 



A. Young stage represented enclosed in 

 the egg-membrane. The medullary plate is 

 distinctly formed, but no part of the medullary 

 canal is closed, bl. blastopore. 



B. Older embryo after the closure of the 

 medullary canal, oc. optic vesicle. Behind 

 the optic vesicle are seen two visceral arches. 



FIG. 78. LATERAL VIEW OF AN ADVANCED EMBRYO OF BOMBINATOR. 



(After Gotte.) 



a. mid-brain , a', eye ; b. hind-brain ; d. mandibular arch ; d ' . Gasserian ganglion ; 

 e. hyoid arch; e'. first branchial arch; /. seventh nerve; /'. glossopharyngeal and 

 vagus nerve ; g. auditory vesicle ; *. boundary between liver and yolk-sack ; k, suctorial 

 disc; /. pericardial prominence; m. prominence formed by the pronephros. 



is not so conspicuous a feature in the Amphibia as in most other 

 types, owing to the small size of the cerebral rudiment. The 

 mid-brain is shewn at fig. 78 a forming the termination of the 



