EMBRYOLOGY OF CRYPTOBRANCHUS 



509 



At the close of Stage 13 the neural grove has reached a length 

 of about 124 degrees; its anterior end usually lies quite accurately 

 at the upper vertical pole, while the neural folds extend about 

 16 degrees in front of it. We have seen that the closing blasto- 

 pore marks the approximate position of the vegetal pole; this 

 pole has now rotated a total distance of 56 degrees from the ver- 

 tical axis. 



63 



64 



Fig. 163 Diagram of an embryo of Cryptobranchus allegheniensis at the close 

 of Stage 13, showing the position of the neural plate and neural folds with refer- 

 ence to the morphological and the vertical axes; m, morphological axis; v, vertical 

 axis. 



Fig. 164 Diagram showing the position of the embryonic body of Crypto- 

 branchus allegheniensis, and illustrating some features of embryo-formation; 

 a to b (72 degrees), portion of the embryo formed in situ; 6 to c (60 degrees), por- 

 tion formed by overgrowth of the dorsal lip of the blastopore, with the possibility 

 of concrescence; c to d (roughly estimated at 16 degrees), portion undoubtedly 

 formed by concrescence; d to e (60 degrees), distance traveled by the ventral lip 

 of the blastopore. Other lettering as in the preceding figure. 



We now have sufficient data for a statement of the position 

 of the embryonic body on the egg, and for pointing out certain 

 features of its mode of formation (figs. 163 and 164). About 

 72 degrees of the anterior end of the embryo is formed in situ. 

 About 60 degrees is formed in connection with the overgrowth 

 of the dorsal lip of the blastopore; in this case there is the possi- 

 bility of concrescence through the apposition of material on each 



