EMBRYOLOGY OF CRYPTOBRANCHUS 105 



area and blastodisc there is left a crescentic area which retains the 

 usual color of the heavily yolk-laden portions of the egg; this 

 region often shows numerous fissures in the yolk, running parallel 

 to the margin of the sperm area. These fissures separate the 

 layers previously mentioned. In position and outline this area 

 corresponds very nearly to the 'gray crescent' of the frog's egg 

 (Roux, '83, '85, '87 and '03; Schultze, '00; see also Jenkinson, '09, 

 p. 80 and fig. 43). 



Within eight to twelve hours after fertilization the sperm 

 pits have become indistinct and, as a rule, they all disappear 

 before the first cleavage, though cases have been found as late as 

 the fifth cleavage stage. Meanwhile the sperm areas also become 

 indistinct, losing the dark line which serves as a boundary and 

 gradually blending with the surrounding surface of the egg. Fif- 

 teen or twenty hours after fertilization, it is usually impossible 

 to orient the egg with respect to the point of entrance of a sperma- 

 tozoon; before the egg is ready for first cleavage it has resumed 

 the general appearance of radial symmetry which it had before 

 fertilization. 



The sperm areas have not been observed in living material, but 

 the examination was made without the aid of a binocular micro- 

 scope, an instrument which has proved of great value in the sur- 

 face study of the fertilization stage with preserved material. 



In preserved material a space sometimes appears between the 

 blastodisc and the vitelline membrane which elsewhere closely 

 invests the egg. An examination of living eggs at intervals from 

 fertilization to first cleavage shows that normally the vitelline mem- 

 brane fits closely about the entire egg. The condition noted in 

 preserved material is due to the subsidence of the blastodisc; 

 the vitelline membrane does not spring away from the egg after 

 fertilization, as occurs in some lower forms. 



If one remove an unfertilized egg from its gelatinous envelope 

 and immerse it in water, and place almost in contact with it a drop 

 of seminal fluid, one observes that the spermatozoa by means of 

 slow writhing movements disperse gradually in all directions. 

 There is no evidence of attraction by the egg, but spermatozoa 

 coming in chance contact with it adhere to its surface, so that in 



