HABITS OF CRYPTOBRANCHUS ALLEGHEN1ENSIS. 



2 9 



until they reach the dorsal lip of the blastopore, which by this 

 time has narrowed to a very small circle. The development of 

 the neural folds proceeds rapidly until their closure a day or two 

 after their first appearance. 



Eighteenth Day Embryos. — In from two to three weeks after 



Fig. 7. Embryos of Cryptob ranch us allegheniensis, about 1 8 days old, within egg 

 capsules. Natural size. 



fertilization the embryos reach the condition represented in Fig. 

 7. At about this time the rudiments of the external gills appear. 

 A broad horizontal pink band along the left side of the yolk sac 

 indicates the beginning of the vitelline vein. The dorsal surface 

 becomes slightly pigmented, the pigment spots being grouped 

 metamerically (cf. McGregor, '97). The embryos squirm slightly 

 when placed in the fixing fluid. 



