EMBRYOLOGY OF CRYPTOBRANCHUS 



515 



183 184 185 



Figs. 180 to 185 Antero-dorsal views of embryos of Cryptobranchus alleghe- 

 niensis in Stage 15. Camera drawings finished under binocular, from preserved 

 material. Figure 182 is drawn from the embryo photographed for figure 234; 

 figure 184 is drawn from the embryo photographed for figure 233. X 6. 



of the embryo involves a noticeable increase in the antero-poste- 

 rior dimension of some of the neuromeres. 



Stage 15: {figs. 180 to 189; 233 and 234). This stage is reached 

 about eighteen hours later than the beginning of the preceding 

 stage. 



In the following account, each neuromere is designated by 

 the number of the groove bounding it on the posterior side. 

 Neuromeres 1 and 2 have usually coalesced; neuromere 4 dis- 

 appears during this, if not in the preceding stage. More definite 

 swellings now occur in neuromeres 1, 2, 3 and 5; the region between 

 Grooves 5 and I is less clearly segmented and is usually somewhat 

 depressed. The outlines of the neural folds in the head region. 



