SEVENTH ANNUAL MEETING 37 



fertilizin combine with the spermophile group of the adjacent fer- 

 tilizin (b and c) and thus block the way for supernumerary sperma- 

 tozoa. This is the postulated mechanism for prevention of poly- 

 spermy. 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 dif- 

 ferent 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-re- 

 ceptors. Purely hypothetical. 



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

 species. The ovophile group of the fertilizin is occupied by mole- 

 cule 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 nor- 

 mally arrive at the egg-membrane loaded with combined fertilizin. 

 This fact, however, makes no essential difference in the theory, and 

 its representation would complicate the diagram. 



We therefore came to the conclusion that the substance 

 which we have been calling - fertilizin is the active agent in 

 fertilization. That it possesses two side chains, one of which 

 is spermophile, combining with certain elements of the sperma- 

 tozoon (sperm receptors), the other of which (the ovophile) 

 combines with certain elements in the egg (egg receptors). 

 Fertilization is therefore not a two-body but a three-body re- 

 action. Of these one is carried by the spermatozoon, the sperm 

 receptors, and one by the egg, the egg receptors. The third, 

 (fertilizin) is produced by the egg and reacts with both the 

 others. The essential reaction in fertilization must be re- 

 garded as that of the fertilizin with the egg receptors ; and the 

 spermatozoon must be regarded as playing the secondary role 

 of activator. In parthenogenesis the active body is still the 

 fertilizin, and the various parthenogenetic agents, in this case 

 play the role of activators. Thus parthenogenesis and fer- 

 tilization may be regarded under one point of view. 



The diagram represents the foregoing theory with the aid 

 of symbols. Sector one illustrates the relation of the side 

 chains before fertilization. Sector two illustrates normal fer- 

 tilization. Some of the consequences of the theory are indi- 

 cated as follows : 



1. (Sector 3). If the egg loses its fertilizin it cannot be 

 fertilized. This we have already seen. 



