37 



acoompanles the sperm-vesicle into the egg» Is "best explained 

 "by supposing that the first vesicle that comes in contact 

 with the cytoplasm initiates a flowing movement of the latter 

 along the inner surface of the shell, from all sides towards 

 the newly entered vesicle. The cytoplasm moving thus along 

 the inner surface of the shell towards one point would he de- 

 flected in towards the center of the Qggt and would tend to 

 carry the vesicle in with it. We may suppose further that 

 when the cytoplasm has once responded to such a stimulus its 

 physiological state is so changed that it will not respond 

 to another. As a result only one vesicle becomes imbedded 

 In the cytoplasm of the egg where it is to be treuasformed in- 

 to the male pronucleus. 



The vitelline membrane (Pig. 104, v.) is formed just after 

 the entrance of the sperm-vesicle into the cytoplasm and 

 the vesicles that failed to enter lie between it and the 

 shell of the egg» The first polar body (Pig. 114) which is 

 cast off while the eggs are passing through the oviduct is 

 also found between the vitelline membreme and the shell. 



The first step in the transformation of the sperm-vesi- 

 cle into the male pronucleus is a thickening of its lateral 

 walls. This may be observed in Pigs, 105 to 111. Accompany- 

 ing this there is an increase of affinity for the stains used 

 (thionln and Delafield's haematoxylin) . Uext there seams to 

 be an extrusion of the old capsular wall which, if we recall 

 the method of the eversion of the sperm, we know, forms the 

 inner lining of the sperm-vesicle. The discarding of this 

 capsular wall was not clearly made out, bnt Pigs. 109 and 110 



