EMBRYOLOGY OF CRYPTOBRANCHUS 533 



median line. The vitelline veins develop more rapidly on that 

 side of the yolk sac which happens to be uppermost. Soon after 

 the hatching period, the vitelline veins of one side degenerate, 

 while those of the other side reach their fullest deveslopment ; 

 the veins of the right or the left side persist in about an equal 

 number of cases. Probably the position of the embryo during 

 the stages when it lies continuously on one side is the factor that 

 determines which set of vitelline veins shall gain the ascendancy. 



The newly hatched larva retains a supply of j^olk sufficient 

 to last it from two to four months. 



The tail of the early larva is proportionally much larger than 

 in the adult. 



Pulmonary respiration is established about five months after 

 the hatching period. 



The metamorphosis takes pUce at the end of the second year. 



Sexual maturity is attained, probably at the end of the fourth 

 year, with a body length of at least 30 cm. for the male and 35 

 cm. for the female. 



X. TIME RECORD 



For the characteristics of the different stages reference is niade 

 to the text and illustrations, especially the photographs. For 

 methods used in obtaining the time record, see the introduction 

 (Section VI). Table 1, page 534. 



XI. ABNORMALITIES 



The present section deals primarily with abnormalities found 

 in embryos taken from their natural environment, or kept under 

 conditions as nearly normal as possible. 



1. Large yolk plug 



In the early stages of development the most common abnormal- 

 ity is the presence of an unusually large yolk plug. Examples 

 are shown in figures 198 and 199, though these are far from rep- 

 resenting extreme cases. In well-marked examples the blasto- 

 pore forms a complete circle only a little below the equator, and 



