EMBRYOLOGY OF CRYPTOBRANCHUS 529 



those taken from their natural habitat indicates that the meta- 

 morphosis occurs at the end of the second year. 



At the time of hatching, the embryo retains a supply of yolk 

 sufficient to last it for several months; the mouth is still quite 

 ventrally situated. So far as its method of nutrition is concerned, 

 during this period the young Cryptobranchus is an embryo rather 

 than a larva. Gradually the yolk disappears, and the mouth 

 assumes a terminal position. Specimens reared in the laboratory 

 begin to take food about two to four months after hatching ; they 

 must be fed individually with bits of scraped beef. No notice 

 is ordinarily taken of the food unless it is moved about imme- 

 diately in front of the animal and preferably a little to one side of 

 the mouth. Some of the specimens take food more readily, and 

 grow more rapidly, than others. One lot of larvae, reared in 

 the laboratory, ate young frog tadpoles. A 12 cm. specimen 

 taken from its natural habitat ate a large Corydalis larva; another 

 newly captured 12 cm. specimen regurgitated a partly digested 

 6 cm. larva of its own kind. 



During the first month after hatching, the vitelline veins of 

 one side of the yolk sac degenerate, while those of the other side 

 shift to a more nearly median position (fig. 197). Degeneration 

 of the right or the left vitelline vein takes place in about an equal 

 number of cases. It has already been noted that in those stages 

 when the embryo lies continuously on one side the vitelline veins 

 are best developed on the uppermost side; furthermore that 

 the embryo falls on the right or the left side in about an equal 

 number of cases. The facts strongly suggest 'that the position 

 of the embryo during the period when the vitelline veins are 

 developing is the factor that determines on which side the vitel- 

 line vein shall persist; but since making these observations I 

 have had no opportunity to put the matter to a rigid test. 



With the reduction of the yolk sac, the vitelline circulation 

 suffers a corresponding diminution in extent; during the late 

 stages of this process, through the increasing thickness and opac- 

 ity of the ventral body wall the vitelline veins are somewhat 

 obscured. 



