268 LIBBIE H. HYMAN. 



well marked and occurs very suddenly, at the moment before 

 membrane elevation is initiated. At this moment, the cytoplasm 

 flows less readily than before and cuts and gashes made with the 

 needle close up more slowly. The viscosity increases during the 

 elevation of the membrane but appears to reach a maximum in 

 a very short time. 



We may therefore speak of an increased viscosity or gelation 

 of the egg cytoplasm as one of the changes included in the fer- 

 tilization reaction. I believe this gelation to be responsible for the 

 roughening of the egg surface at fertilization. As Rhumbler 

 ('05) has recognized, a rough and crenated surface is causally 

 related to a solidified condition of protoplasm. As the roughen- 

 ing of the egg begins at the point of contact of egg and sperm and 

 spreads from there over the egg, it follows that the gelation 

 process must likewise originate at the site of sperm entry and 

 progress from this point in all directions. It seems probable that 

 the gelation process is confined to the cortex of the egg since in 

 egg fragments only the original surface roughens at fertilization. 



The interpretation of the rounding up of egg fragments re- 

 mains to be considered. 1 I at first thought this to be another 

 indication of increased viscosity, of the increased tension accom- 

 panying the change from a more fluid to a more viscous state. 

 But obviously gelation cannot cause both a rounding up and a 

 roughening. Although the surface tension of gels is higher than 

 that of sols, still surface tension is not great enough to induce 

 sphericity in fragments of gels. It therefore seems necessary to 

 conclude that the rounding of egg fragments indicates a decreased 

 viscosity or increased fluidity. As my observations show that 

 this process precedes the roughening by a quite perceptible time 

 interval, it seems that the cortex of the egg at fertilization first 

 becomes more fluid and then undergoes gelation. Just ('22) 

 emphasizes a liquefaction of the cortex as part of the fertilization 

 reaction. 



The gelation of the egg at fertilization serves at least two 

 purposes: (a) the vitelline membrane is split from the egg cyto- 



1 Harvey ('10) has also emphasized the rounding up of eggs at fertilization and 

 attributes it to an increase in tension. However, the same tension will induce 

 sphericity if the cytoplasm becomes more fluid. My observations on egg fragments 

 indicate that this change in tension is in the cortex, not in the membrane. 



