GENERAL PROPERTIES OF THE ECTOPLASM 



off the &gg, the ectoplasm again builds a new surface-struc- 

 ture, the hyaline plasma-layer. 



Before the actual separation of the vitelline membrane, 

 an ectoplasmic change beginning at the point of sperm- 

 entry sweeps over the egg which immunizes it to other 

 spermatozoa, the pole opposite the site of sperm-entry 

 being the last point affected. The site of sperm-entry 

 becomes a "point of injury" and is "negative" to the entry 

 of spermatozoa arriving at this point, all other points around 

 the egg for a brief moment being "positive." Especially 

 in slowly reacting eggs it can be noted that this "wave of 

 negativity" moves over the egg, at a rate which varies 

 with that at which the sperm-head disappears within the 

 ectoplasm. When only the tip of the sperm-head has 

 entered the ectoplasm, the immediate vicinity of the site 

 of penetration can not engulf another spermatozoon. As 

 more of the sperm-head disappears within the ectoplasm, 

 the "negativity" to sperm-entry progresses still farther 

 around the egg; when the head has disappeared, the egg 

 can engulf sperm only at one point — the pole opposite 

 that at which the spermatozoon entered the egg. The 

 "wave of negativity" thus precedes the actual beginning of 

 membrane-separation. Before the membrane begins to 

 separate at the site of sperm-entry, other spermatozoa can 

 no longer enter at any point on the egg. From the point of 

 sperm-entry a definite gradient of membrane-separation is 

 established. This gradient, therefore, follows that of loss 

 of susceptibility to sperm-penetration. 



When a spermatozoon becomes attached not only the 

 penetration of other spermatozoa but also their fixation to 

 the egg depends upon the degree of penetration of the effec- 

 tive spermatozoon, that is, on the rate at which the "wave 

 of negativity" is propagated around the egg. Thus, at the 

 beginning of penetration, other spermatozoa can not become 

 attached to the egg in the immediate neighborhood of the 



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