556 FRANK R. LILLIE 



undergone some 'physiological' change which prevents union with 

 the sperm. The first theory is an old one based on conditions 

 in the sea-urchins; it is inapplicable to the ova of most animals, 

 which do not form special membranes after f ertilizaftion ; what- 

 ever value the fertilization membrane may have in special cases 

 as guarding against polyspermy, it has been shown for some cases 

 at least that the real cause of failure of refertilization is more 

 deeply seated. Thus Wilson ('03) shows for Cerebratulus that 

 after the germinal vesicle has faded, cytoplasmic fragments 

 devoid of nucleus may be fertilized and undergo typical mero- 

 gonic development; but enucleated fragments of fertilized eggs 

 are incapable of refertilization: "Even when such fragments 

 are placed in water containing sperm immediately after the sec- 

 tion before they have assumed a spherical form, they fail to 

 fertilize, though spermatozoa may be observed adhering to their 

 periphery." Wilson rightly attributes the sterility of such frag- 

 ments to a physiological change of the cytoplasm. 



The theory of a physiological change of the cytoplasm follow- 

 ing fertilization has been generally accepted, but there has been 

 no idea of the nature of the change involved. Wilson directs 

 attention to the similar sterility of egg fragments prior to fading 

 of the germinal vesicle and suggests that the cytoplasmic change 

 following fertilization is physiologically the opposite of that 

 following the fading of the germinal vesicle. Now, as I have 

 shown the probability that the agglutinating substance is not 

 present in an active form in Arbacia prior to fading of the germinal 

 vesicle, and that it becomes neutralized by union with anti- 

 fertilizin following fertilization, it is clear that this mechanism 

 answers the requirements of the problem. The fundamental 

 mechanism for the prevention of polyspermy is the neutralization 

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

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

 anti-fertilizin.^ 



^Noto: Delage ('01) determined for Asterias glacialis that fragments of the 

 ovocyte with intact germinal vesicle are sterile, so that merogony cannot be 

 produced. As soon as the germinal vesicle fades fragments are fertilizable and 

 merogonic development may follow. Wilson's observations are in accord with 



