THE BIOLOGY OF THE CELL SURFACE 



point. Thus an electro-negative wave sweeps along the 

 nerve fibre as the impulse traverses it. 



During the transmission of the nerve-impulse there are 

 no visible structural changes in the nerve. The propaga- 

 tion of the effect of sperm-attachment over the surface of 

 the egg, however, is clearly visible. Thus, in the egg of 

 Arbacia a wave of turbidity followed by one of lightening 

 marks its course. In the egg of Echinarachniiis it reveals 

 itself: by the behavior of supernumerary spermatozoa that 

 are in contact with an egg and are brought to a standstill 

 progressively, the ones nearest the site of sperm-entry being 

 first quieted; by progressive dissolution of ectoplasmic 

 colloids; and by the break-down of pigment granules in the 

 jelly that encloses the egg. 



Also the response of the ectoplasm during the period of 

 membrane-separation to exposure to hypotonic sea-water 

 reminds us of the action-current in a stimulated nerve. 

 The high degree of susceptibility of the ectoplasm in the 

 zone of membrane-separation and the resistance in the 

 zones from which the membrane has not yet separated or 

 from which it is completely lifted again suggest the electro- 

 negative condition in the nerve fibre. ^ It may well be that 

 this is more than a superficial resemblance; and for this 

 reason these ectoplasmic responses would warrant further 

 investigation. 



Whilst the egg passes through the period of surface 

 changes under discussion, another property of the ectoplasm 

 rises to sharp visibility, its contractility. Of the eggs 

 described above, that of Nereis is the best in which to 

 observe the shrinking and expansion following insemination. 

 But this phenomenon can be followed in other eggs. Met- 

 schnikoff years ago called attention to the contractile power 



1 Lillie, R. S., 1922. 



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