426 Lei and Griggs. 



Historical Review 



Research in the field of amphibian embryology has already 

 yielded results of considerable value. Neuromeres have been 

 observed not only in the neural plate but also in the neural crests 

 and the neural tube; the anlage of the lateral eyes has been 

 traced back to pigment spots, and the early origin of the ear 

 in relation to lateral line organs has been observed. 



Before reviewing these topics, however, it will first be neces- 

 sary to clear the way by considering two minor points, which 

 have been the cause of considerable confusion, the closing of 

 the blastopore and the formation of a series of grooves in front 

 of the blastopore. 



The closing of the blastopore has been made the subject of 

 extensive research. It is agreed that the circular form by a 

 more rapid inward lateral growth becomes an oval, then a nar- 

 row slit. The next change, however, is a matter of dispute. 



Jordan ('93) finds that in the newt Diemyctylus the next 

 step is a fusion of the walls of the slit for a very short distance 

 either at the posterior end or at the anterior end or, as is more 

 usual, at both ends at once. Next there is a fusion of the two 

 walls at the center of the slit. Thus there are formed two tem- 

 porary pores the distance between which is slightly less than 

 the original diameter of the circular blastopore. The anterior 

 of these two pores is the opening of the neurenteric canal and 

 the posterior one becomes the anus. 



Eycleshymer ('95) in his study of Ambly stoma and Rana 

 palustris confirms Jordan's statement of the origin of the anus 

 and of the neurenteric canal but he does not describe any pre- 

 liminary fusing at the ends of the slit-like blastopore. He finds 

 that there is occasionally "si pear-shaped opening with the 

 smaller end anterior instead of the usual dumb-bell outline." 

 He describes the position of the anus when first formed as lying 

 just outside the neural crest. 



Morgan ('97) finds that in the Urodeles the anus is formed 

 as described by Jordan and Eycleshymer but in the Anura here 

 is a concrescence o the slit-like blastopore posteriorly and 



