GENERAL PROPERTIES OF THE ECTOPLASM 



have made observations on thousands of eggs and have yet 

 to see an egg exposed during membrane-separation break in 

 those regions from which the membrane is not lifting. This 

 is especially well brought out by exposing eggs during the 

 early stages of membrane-separation; for then only that 

 part of the egg from which the membrane is just lifting, at or 

 near sperm-entry, is susceptible to dilute sea-water. 

 Similarly, any part of the egg from which the membrane has 

 fully lifted is resistant, as is strikingly shown by exposing eggs 

 just at the moment when the membrane is being lifted from 

 the last point on the egg-surface. Then the break-down is 

 only at this point; the zones from which the membrane is 

 already off are resistant. When the membrane is fully off, 

 the egg leaves the period of susceptibility. We may say, 

 therefore, that a wave of resistance to dilute sea-water 

 follows in the wake of the wave of susceptibility. There 

 is an exceedingly rapid restitution-process in the ectoplasm 

 following a momentary loss of resistance through the normal 

 break-down of material in the ectoplasm which pushes off 

 the vitelline membrane. 



If we attempt to come to some conclusion as to the mean- 

 ing of this susceptibility, we must take into account the 

 following facts: First, the resistance of the ectoplasm in 

 those regions from which the membrane has not yet sepa- 

 rated; second, the very rapid recovery of the ectoplasm 

 after membrane separation; third, the apparent failure of ^ 

 the ectoplasm at the site of sperm-entry to show any greater 

 susceptibility than the remainder of the egg-surface. In 

 brief, we must keep in mind that this susceptibility is, 

 clearly localized; or, what is more correct, that the break 

 in the t^g which is the expression of decreased resistance 

 to the hypotonic sea-water is only at the site, and in the 

 moment, of membrane-separation. Now this does not 

 mean that only at this point water enters the egg. Rather, 

 it indicates that the point at which the membrane is sepa- 



III 



