STUDIES OF FERTILIZATION 563 



phile combining group of the fertilizin which then seizes upon 

 egg receptors, and it is the latter union which results in membrane 

 formation. If this were so, it is obvious that the spermatozoon 

 is only secondarily a fertilizing agent, in the sense of initiating 

 development, and that the egg is in reality self-fertilizing, an 

 idea that agrees well with the facts of parthenogenesis and with 

 the amazing multiplicity of means by which parthenogenesis 

 may be effected. For the agents need only facilitate the union 

 of the fertilizin and egg receptor. 



The inhibiting action of the blood, from this point of view, is a 

 deviation effect due to occupancy of the ovophile group of th^ 

 fertilizin, either because the inhibitor in the blood is an anti- 

 body to the fertilizin or because it possesses the same combining 

 group as the egg receptor. In such a case, the ovophile group 

 of the fertilizin being already occupied by the inhibitor, fertili- 

 zation could not take place. 



This theory transfers the fertilizing power from some hypo- 

 thetical substance contained in the spermatozoon to a definite 

 substance contained in the egg itself, in relation to which the sperm 

 acts merely an as activator. It does not necessarily predicate 

 the precise mode of action of the fertilizing substance although 

 the assumption is here made that chemical union with certain 

 molecules in the egg, called egg receptors, is a necessary part of 

 its action. 



In the present section we shall proceed to examine the evidence 

 for the existence of an ovophile as well as a spermophile combin- 

 ing group of the fertilizin. 



1. THE INHIBITING EFFECT OF BLOOD OF THE SEA-URCHIN UPON 

 FERTILIZATION OF EGGS OF THE SAME SPEClES 



It is a common practice of embryologists to wash the eggs of 

 marine invertebrates, which they propose to fertilize, twice or 

 several times with sea-water, because it is a matter of experience 

 that this procedure very greatly increases the proportion of eggs 

 that fertilize. However, I know of no study of this really very 

 striking phenomenon. The eggs are usually obtained for fertili- 



