EMBRYOLOGY OF CRYPTOBRANCHUS 107 



first cleavage. About the time of the appearance of the pit 

 at the animal pole, the egg becomes capable of fertilization. 



The point of entrance of a spermatozoon (the 'sperm pit') is 

 easily recognizable in both living and preserved eggs. In pre- 

 served material, the influence of the spermatozoon on the egg sub- 

 stance is indicated in surface views by the differentiation of a 

 large circular area (the 'sperm area') surrounding the sperm pit. 

 This area is recognizable by a slight difference in color and by the 

 presence of a bounding dark line; it increases in size until it covers 

 nearly a hemisphere of the egg, then disappears. 



In artificially fertilized eggs, and presumably in eggs fertilized 

 in nature, polyspermy usually occurs. 



There is no evidence of attraction of the spermatozoon by the 



egg. 



The spermatozoon may enter the egg at any point, but sperm 

 areas are best developed about those sperm pits that occur near 

 the margin of the blastodisc. 



V. THE INTERNAL HISTORY OF THE EGG BEFORE CLEAVAGE 



The present section deals with a few features concerned in 

 ovogenesis and maturation, and gives a more detailed account of 

 the fertilization phenomena. 



A. OVOGENESIS 



The material for this study consists as follows: 



(a). For the early stages it was found best to use larval and 

 immature post-larval females, with a body-length ranging from 

 9 to 38 cm. (two years old and upward). Females with a body 

 Length of more than 38 cm. are almost always sexually mature. 



(b). The residual eggs of spent females taken in September 

 furnished ovocytes sHghtly older than those of the largest imma- 

 ture females taken in August and September. 



(c) . Mature females -taken during July and August furnished 

 material for the late stages of ovogenesis. 



There remains a period during the last year of development, 

 extending from October to June inclusive, which is not represented 



