SPERM-EGG INTERACTING SUBSTANCES, I 29 



bine with univalent fertilizin and therefore sustain a loss in fertiliz- 

 ing capacity because a certain number of combining groups on 

 their surfaces, which would otherwise be used during the union of 

 the spermatozoa with homologous eggs, are covered by fertilizin 

 molecules. No agglutination occurs because the fertilizin molecules, 

 being univalent, only have one combining group per molecule. 

 The univalent fertilizin concept provides an explanation of the 

 apparent absence of fertilizin in many organisms. The egg water 

 of Cumingia tellinoides (Sampson, 1922), of Urechis caupo (Tyler, 

 i94i«) and of the starfish Patiria miniata (Brandt) (Metz, 

 1945) does not cause agglutination of homologous spermatozoa. 

 Metz was able to make these starfish spermatozoa agglutinate in 

 the presence of egg water by the addition of an adjuvant, hen's 

 egg-white, which, in the absence of starfish egg water, did not 

 cause sperm agglutination. Again, there is an analogy in the field 

 of Rh antibodies. These are quite often found in a non-agglutinat- 

 ing, univalent form and can be made to agglutinate Rh-positive 

 cells by such substances as serum albumin (Race, 1944; de Burgh, 

 et al., 1946). Furthermore, multivalent immune antibodies can be 

 converted into univalent forms by treatments similar to those 

 which have been used on fertilizin (Tyler, 1945). 



Zone phenomenon. The resemblance between the behaviour of 

 spermatozoa in the presence of fertilizin and serological reactions 

 is strengthened by the occurrence of the zone phenomenon (Tyler, 

 1940a). In serological reactions the zone phenomenon refers to 

 the fact that maximum or most rapid agglutination or precipita- 

 tion only occurs when antigens and antibodies are mixed in par- 

 ticular proportions. The zone phenomenon provides an interpre- 

 tation of the conditions in which feeble sperm agglutination is 

 observed, for if fertilizin molecules are present in great excess, 

 there will be enough of them to saturate all the combining groups 

 on individual spermatozoa without the necessity for sharing of 

 fertilizin molecules by numbers of spermatozoa, with consequent 

 agglutination. Alternatively, the intensity of the agglutination re- 

 action may be reduced if univalent as well as multivalent fertilizin 

 molecules are present in egg water and the former are nearly able 

 to saturate the combining groups on the spermatozoa. Zone 

 phenomena have been observed and studied in the spermatozoa 

 of Lytechinus pictus by Spikes (1949a). 



Role of egg jelly in fertilization. Although the description of the 



