EMBRYOLOGY OF CRYPTOBRANCHUS 



505 



155 



156 



157 



158 



Figs. 151 to 158 Stage 13. A series of embryos of Cryptobranchus alleghe- 

 niensis showing early stages in the formation of the neural folds and the segmenta- 

 tion of the neural plate. Camera drawings, finished under the binocular, from 

 preserved material. I, II and III indicate the earliest transverse grooves; 1, 

 2, 3, grooves appearing a little later, numbered consecutively and not in the order 

 of appearance. X 6. 



tion that the surface just outside of the neural folds becomes 

 very much roughened and traversed by fissures parallel to the 

 folds, indicating stresses and the rapid shifting of material. 

 During the later part of this stage a pair of less conspicuous 

 transverse folds appear lateral to the anterior end of the neural 

 plate (fig. 158); the significance of these folds has not yet been 

 determined with certainty (but see Stage 15). 



The first transverse groove to cross the neural plate is shown 

 in figure 152. A little later, two transverse grooves appear in 

 rapid succession posterior to it. These first three transverse 



JOURNAL OF MOBPHOLOar, 70L. 23, NO. 3 



