EMBRYOLOGY OF CRYPTOBRANCHUS 519 



most amphibian eggs the blastopore is very late in closing. In 

 late stages the blastopore has the form of an anchor or an inverted 

 T; the posterior transverse portion remains longest as an open 

 slit, and the center of this transverse portion never completely 

 closes but persists as the anal or cloacal apertme. 



The posterior end of the embryo forms approximately at the 

 vegetal pole. At the time when the neural folds are first formed 

 the embryo has a total length of about 148 degrees, hence its 

 anterior end does not reach the animal pole. About 72 degrees 

 of the anterior end of the embryo (nearly half its total length) 

 is formed in situ; about 60 degrees posterior to this is formed by 

 overgrowth with the possibility of concrescence. Only a very 

 small part at the posterior end, perhaps 16 degrees, is formed by 

 the meeting of the lateral and ventral lips of the blastopore; this 

 part is undoubtedly formed by concrescence. 



From the time of its first appearance the neural groove is con- 

 tinuous with a median notch in the dorsal lip of the blastopore. 

 There is evidence that the neural groove early acquires a segmented 

 structure. 



Transverse grooves, definite in number and location, cross 

 the neural plate, dividing it into true segments or neuromeres. 

 In the region- of the mesoblastic somites the transverse grooves 

 of the neural plate are in line with the intersomitic grooves, and 

 the neuromeres are in line with the somites. Segmental flexures 

 of the neural folds sometimes occur; in these cases the outward 

 flexures of the neural folds are in line with the transverse grooves, 

 and the inward flexures are in line with the neuromeres. 



At the time of the closure of the neural folds, the embryo has 

 increased in length so that it extends over about one-half of the 

 circumference of the egg. 



IX. DEVELOPMENT AFTER THE CLOSURE OF THE NEURAL FOLDS 

 A . Description by stages, to the time of hatching 



Most of the important features of the later external develop- 

 ment are sufficiently illustrated by the photographs. Only a 

 brief account is here necessary and this will deal principally with 



