FERTILIZATION REACTION IN ECHINARACHNIUS PARMA. Q 



minutes after insemination a thin film forms on the surface of 

 the cytoplasm (Fig. n) the hyaline plasma layer, or gelatinous 

 film of Loeb. 



Experiments are being made at present with the hope of ana- 

 lyzing farther these cortical responses of the Echinarachnius egg 

 to the sperm. We may, however, point out in conclusion to 

 these observations that in the progressive membrane lifting and 

 the cortical change that precedes it we have another of the numer- 

 ous examples of an activity gradient; this of course is distinct 

 from the primary axial (polar) gradient that exists in echinoderm 

 eggs (see Child). In following these waves of cortical change 

 we are actually viewing the propagation of the effect of a stimulus 

 in an irritable cell. One effect of this stimulus of sperm entrance 

 is to alter the plasma to such an extent that it prevents the 

 entrance of other sperm. It is not the membrane that is a block 

 to polyspermy; that block ex ; sts before the membrane lifts off. 

 The membrane is merely the sign and consequence of more 

 profound cortical changes. 1 In a way, it is of no significance 

 that the membrane rises sharply into visibility provided these 

 primary cortical changes take place. And indeed I have seen 

 any number of eggs fertilize and develop without throwing off 

 membranes. Such eggs are as incapable of reinsemination as 

 eggs that have formed membranes. In the Echinarachnius 

 egg, then, normal development has been already initiated by 

 the sperm when the membrane begins to form. 



1 Says Lillie: "The fundamental mechanism for the prevention of polyspermy is 

 the neutralization of the fertilizin by the anti-fertilizing present in the egg; i. e., 

 the occupancy of the spermophile side-chain of the fertilizin by the anti-fertilizin. 



"The question may be raised why such neutralization of the fertilizin is delayed 

 until the moment of fertilization? The answer to this difficulty is fairly clear. 

 The fertilizin is located in the cortex of the egg, and the anti-fertilizin is more deeply 

 situated; they therefore do not interact so long as the cell body as a whole is 

 quiescent. But as soon as the cortical fertilizin becomes activated by union with 

 the sperm it at once begins to attach certain substances in the egg, as demonstrated 

 in the third part of this paper; this sets up diffusion evidenced by escape of pig- 

 ment, and by cytoplasmic flowing, and the two substances are brought together 

 and interact. While this explanation is partly hypothetical, the spatial separation 

 of the fertilizin and anti-fertilizin and the quiescent character of the cell-body in 

 the unfertilized egg are facts; so also are the movements of diffusion and the cyto- 

 plasmic currents set up on fertilization." 



