THE PHYSIOLOGY OF FERTILIZATION 161 



to sea- water of normal temperature and composition, 

 the eggs develop normally to the formation of larvae. 

 If, however, the process is interrupted too soon, the egg 

 is able only to begin the first processes; but within a 

 suitable period of time renewal of the action to the 

 optimum extent will bring about complete activation. 

 The activation process can thus be arbitrarily inter- 

 rupted and resumed, and this with either high tempera- 

 ture or butyric acid alone, or with combination of the 

 two in either order. The optimum time of exposure 

 to high temperature shows a very high temperature 

 coefficient (Q IO = 200-400) , but the quantitative details 

 do not concern us here (see chap. vii). 



V. POLYSPERMY AND MEROGONY THE PROBLEM OF 



REVERSIBILITY 



The fertilized egg does not react to fresh spermat- 

 ozoa, and these do not enter it. The change which 

 produces this condition takes place so rapidly that only 

 one spermatozoon normally enters, though hundreds 

 may be present in the immediate neighborhood of the 

 egg, and many may reach it apparently simultaneously. 

 The fact of monospermy has been known since the time 

 of the classic researches of Hertwig and of Fol. As is 

 well known, Fol proposed the theory that the fertili- 

 zation membrane prevented entrance of supernumerary 

 spermatozoa and constituted the mechanism for pre- 

 vention of polyspermy. Its formation is, however, 

 much too slow to account for the facts; and it has been 

 repeatedly shown that removal of the fertilization mem- 

 brane does not render the egg more susceptible to 

 superimposed insemination. 



