578 FRANK R. LILLIE ' 



intimate nature of the reactions themselves is unknown. To 

 represent them in terms of the EhrUch hypothesis as definite 

 lock-and-key chemical combinations is of course to go beyond 

 the facts. But it is necessary in some way to gain definiteness 

 of formulation not only for purposes of description, but also to 

 obtain a definite working hypothesis. The method of formu- 

 lation which I have adopted has both of these advantages. In- 

 deed some of the experiments could hardly have been suggested 

 by any other hypothesis. 



1. THE MECHANISM OF FERTILIZATION 



In terms of such an hypothesis the mechanism of fertilization 

 may be summed up in a diagram (fig. 1, sector 1). The cortex 

 of the egg contains the fertilizin (see explanation . of symbols) 

 of which three molecules are represented each with a spermophile 



Fig. 1 In successive sectors of the egg there are represented the mechanism 

 of fertilization and the blocks to the mechanism, as follows : 



Sector 1 The arrangement of substances in the unfertilized egg and in the 

 spermatozoon that are active in fertilization. See explanation of symbols. 



Sector 2 The mechanism of normal fertilization. The sperm receptor unites 

 with the spermophile group of the fertilizin and the egg-receptors with the ovo- 

 phile group of the fertilizin owing to activation of the latter by the sperm (a). 

 Molecules of the anti-fertilizin combine with the spermophile group of the adja- 

 cent fertilizin (b and c) and thus block the way for supernumerary spermatozoa. 

 This is the postulated mechanism for prevention of polyspermy. At the same time 

 molecules b and c of the fertilizin have also united with the egg-receptors. 



Sector 3 Inhibition of fertilization by loss of the active body, fertilizin. 



Sector 4 Theory of antagonistic action of spermatozoa of different phyla. 

 The sperm receptors are occupied by combining groups cast off by the antagonistic 

 spermatozoa. 



Sector 5 Fertilization is blocked by occupancy of the egg-receptors. Purely 

 hypothetical. 



Sector 6 Theory of inhibitory action of blood of the same species. The 

 ovophile group of the fertilizin is occupied by molecules in the blood (inhibitor) 

 possessing the same combining group as the egg-receptors. Molecules of the 

 blood inhibitor also shown in the medium. 



The fertilizin is represented in the diagram as occurring only in the cortex of 

 the egg. But it also occurs in high concentration in the jelly surrounding the egg. 

 The spermatozoon must thus normally arrive at the egg-membrane loaded with 

 combined fertilizin. This fact, however, makes no essential difference in the 

 th#ory, and its representation would complicate the diagram. 



