FERTILIZATION ON PARTHENOGENESIS. 



163 



TABLE II. 



It was to determine whether sperm entered eggs thus treated 

 that a number of series were preserved and sectioned. An 

 endeavor was made to obtain eggs just at the critical point (e. g., 

 at the shortest length) of exposure at which fertilization was 



prevented. 



i. Cytological Observations. 



Sections of such eggs reveal the fact that sperm have entered 

 them in great numbers. Fifteen minutes after insemination 

 sperm are found scattered diffusely at all levels throughout the 

 egg, at the periphery and in the center, some lying very near the 

 egg nucleus. So far as concerns any reaction characteristic of 

 fertilization, it is entirely absent; no asters have ever been found 

 in these eggs, as well as no indication of spindle formation or 

 copulation of pronuclei. 



The sperm heads have begun to lose their normal characteristic 

 shape and have begun to disintegrate; some appear swollen with 

 a tendency to become vacuolated, others appear to be falling 

 apart in fragments. Many dark-staining granules are found 

 through the cytoplasm evidently being derived from broken- 

 down sperm. 



The egg pronucleus has to a great extent lost its power of 

 holding the stain and appears only a shadow of the original 

 nucleus. It is still intact with little or no indication of destruc- 

 tive changes. 



Thirty minutes later (45 minutes after insemination) eggs 

 from the same lot present quite a different picture. The egg 

 nucleus remains intact but does not appear stained. The 

 spermatozoa appear to fall into two very general classes. 



1. Those in which the nucleus has a tendency to disintegrate, 

 scattering heavily staining granules throughout the cytoplasm. 



2. Those that have a tendency to become vacuolated and to 



