6 E. E. JUST. 



point of sperm entry the membrane thoroughly glued to the egg 

 surface is pushed off; the material continuing throughout the 

 cortex to escape progressively lifts off the membrane around the 

 egg. 1 The droplets are squeezed out of the cortex into the per- 

 ivitelline space and may reach the membrane as discrete bodies 



5 



FIG. 5. About two seconds later than Fig. 4. 



FIG. 6. Two to three seconds later than Fig. 5. Note vesicles forming. 



before they fade from view. Often they go into solution more 

 quickly. The membrane thickens slightly after formed. 



As the membrane lifts off, it carries away any supernumerary 

 sperm whose activity is in contrast to immobilized sperm pre- 

 viously engulfed by the egg. Not only is it true that at no 



7 8 



FIG. 7. About two seconds later than Fig. 6. Membrane incomplete at pole 

 opposite entrance-point of the sperm. 



FIG. 8. Twelve seconds after beginning of membrane lifting. The membrane 

 is fully formed but still wrinkled, especially at point at which it lifted last. 



point at which the membrane has elevated can sperm enter, but 

 also that membrane elevation at a given point though not com- 

 plete for the whole egg is a bar to sperm entrance at any point 

 on the egg surface. And th's is the most significant point in 

 the reaction. Before the actual elevation of the membrane, some 

 cortical change beginning at the point of sperm entry sweeps over 



1 This does not mean, however, that the eggs decrease in size after fertilization. 



