STUDIES OF FERTILIZATION 525 



reacting with the sperm which I call the ' spermophile side-chain' 

 or group and the other reacting with the egg which I call the 

 'ovophile side-chain' or group. The chemical group of the sperm 

 which reacts with the fertilizin is named the sperm receptor and 

 that of the egg the egg receptor. 



We are thus furnished with a concrete conception which 

 answers very well for purposes of description; It need not>however, 

 be taken too literally. The theoretical aspect of the results is 

 discussed in section IV. 



The present paper presents in some detail the evidences on 

 which this general conception of fertilization rests; it deals ex- 

 clusively with Arbacia; in a later paper I shall present some 

 confirmatory evidence from the study of Nereis. We shall con- 

 sider first the action of the spermophile side-chain of the fertilizin 

 and the evidence that the latter is a necessary link in the 

 fertilization process. Second, we shall consider the nature of 

 the ovophile side-chain of the. fertilizin, the means of inhibiting 

 its action and of neutralizing such inhibition. 



The terminology has been largely adopted from immunology, 

 because it seemed best suited to express the facts. If it seems 

 rather bizarre to the zoological reader I must ask him not to 

 conceive prejudice for this reason against the facts themselves, 

 which stand on their own feet quite apart from any terminology 

 or theory. The terminology and the theory are significant only 

 to the extent that they give a brief description of the facts, and 

 serve as a working hypothesis. 



II. THE SPERMOPHILE SIDE-CHAIN 



I. A QUANTITATIVE METHOD OF STUDYING THE PRODUCTION OF 



FERTILIZIN BY OVA 



The fundamental fact which forms our point of departure is 

 that fertilizable eggs of Arbacia suspended in sea-water secrete 

 a substance (fertilizin) for which only the spermatozoa of the 

 same species constitute an efficient indicator. Similarly the 

 only cells that produce the substance are the egg-cells of the same 

 species; it is not found in the blood or in extracts of other tissues. 



