FERTILIZATION AFTER INITIATION OF DEVELOPMENT. 285 



Fig. 4 was made from lot III Y 1 (page 283) and perhaps can- 

 not be considered as representing the normal mode of entrance 

 of the spermatozoon of Arbacia but it at least indicates the 

 possible method of entrance. It may be necessary to attribute 

 the appearance of the phenomenon to the general retarded con- 

 dition of the egg protoplasm brought on as a result of the hyper- 

 tonic treatment before insemination, but it would not seem 

 impossible to discover a somewhat similar condition of sperm 





FIG. 4. X 3,000. Part of a section of an egg showing the entrance of the 

 spermatozoon; one has* practically completed its entrance and is rounding up, the 

 other in the process of entrance. From same lot as Fig. 2. 



activity under normal conditions if the right stages were pre- 

 served in a close enough series. Penetration, in Arbacia, is 

 effected much more readily than in Nereis, in which Professor 

 Lillie 1 has illustrated so clearly the entrance of the spermatozoon. 

 The most essential difference in the morphology of the process 

 in the two forms is the absence of the attraction cone in Arbacia 

 which in Nereis forms an attachment for the spermatozoon and 

 apparently pulls the spermatozoon through a small aperture in 

 the vitelline membrane as it recedes from the periphery of the 

 egg. Immediately after the spermatozoon is taken inside the 

 egg it assumes its normal appearance, for no elongated heads 

 have been observed that were not in the act of entering the egg. 



3. Insemination of Pure Cultures of Isolated Blastomeres. 



Since the experimental results of the writer did not agree 

 with the views of Loeb namely, that eggs whose development 



2 See Lillie, F. R., 'n and '12. 



