106 BERTRAM G. SMITH 



time there are more spermatozoa at the surface of the egg than at 

 a httle distance from it. As previously noted, spermatozoa are 

 found in capsules that do not contain eggs; in this case there is 

 no possibility of attraction by the egg. 



In Cryptobranchus, as in other amphibian eggs, there is no 

 preformed micropyle. In eggs fertilized in a natural manner, the 

 spermatozoon may enter the egg at any point. More sperm 

 pits have been found in the marginal region of the blastodisc, 

 about midway between the equator and the animal pole, than 

 elsewhere, indicating that this zone may be especially favorable 

 to the entrance of the spermatozoon ; but if any selective influence 

 is at work, it cannot be a strong one, for spermatozoa have been 

 found penetrating the egg close to the second polar spindle, and 

 at various points in the lower hemisphere, even at the vegetal 

 pole. Sperm areas are best developed about those sperm pits that 

 occur near the margin of the blastodisc. In only one case has a 

 sperm pit at the vegetal pole been found surrounded by a sperm 

 area. Sperm pits are often more numerous on one side of the egg 

 than on the opposite side, indicating a chance inequality in the 

 exposure of the egg to the seminal fluid. 



All the statements in this section regarding penetration of the 

 egg by the spermatozoa have been confirmed by sectioning eggs 

 which have first been carefully described externally. 



D. SUMMARY 



A germinal area is first visible in the ovarian egg taken about 

 the middle of August. The germinal area is usually situated on the 

 more exposed side of the egg, toward the periphery of the ovary; 

 it has at first a diameter of about 60°, and increases gradually in 

 size until about the time of first cleavage ; it has then a diameter of 

 about 145°. 



In ovarian eggs examined about the first of September, the 

 germinal vesicle is usually visible at the surface, in the center of 

 the blastodisc; it disappears shortly before the egg leaves the 

 ovary. 



Soon after the eggs have reached the uterus, a sharply-defined 

 pit appears at the animal pole; this pit persists up to the time of 



