246 



BERTRAM G. SMITH. 



There remains a more problematical phase of concrescence 

 which has been studied in various vertebrates, and which I have 

 recently investigated in the amphibian embryo. The question 

 involved is this: during the process of overgrowth of the yolk 

 by the dorsal lip of the blastopore, is material dorsal to the 

 blastopore carried from both sides toward the median line? In 

 other words, is there a confluence of material in the median 

 line of that part of the embryo that is formed by overgrowth 



blp. 



1 2 



FIG. i. Diagram showing in lateral view successive positions of the blastopore 

 in the gastrula of Cryptobranchus allegheniensis. blp. and blp'. respectively indi- 

 cate early and late positions of the dorsal lip of the blastopore; m is the morpho- 

 logical axis of the egg, and v the vertical axis determined by gravity. The cross 

 indicates the position of the anterior end of the neural groove. 



FIG. 2. Diagram showing in lateral view the position of the embryonic body, 

 and illustrating some features of embryo-formation, in the egg of Cryptobranchus 

 allegheniensis. a to b (72), the portion of the embryo formed in situ; b to c 

 (60), the portion of the embryo formed by overgrowth of the dorsal lip of the blasto- 

 pore; c to d (about 16), portion formed by convergence of the lateral and ventral 

 lips of the blastopore; d to e (60), distance travelled by the ventral lip of the 

 blastopore. Other lettering as in the preceding figure. 



and in-turning of the dorsal lip of the blastopore? The problem 

 as concerns the egg of Cryptobranchus may be more clearly 

 pointed out with the aid of the accompanying figures (Figs. I 

 and 2). In Fig. I the transverse lines indicate successive posi- 

 tions of the blastopore, viewed from the lateral aspect. In 

 Fig. 2 the relative amounts of the embryo formed in different 

 ways are represented : about 72 of the anterior end of the embryo 



