C. B. METZ 37 



binding capacity is increased by a factor of at least 128 in the 

 presence of an adjuvant (Metz, 1945). 



Role of Fertilizin in Fertilization 



The highly specific and dramatic sperm agglutinating action of 

 fertilizin suggests that this agent may play an important if not 

 essential role in fertiHzation. The effect of egg water on sperm 

 motility, respiration, and the sperm acrosome ( see effects of egg 

 water) may result from action of fertilizin. These effects may be 

 aids to or essential for fertilization. 



Evidence concerning a more direct role of fertilizin in fertiliza- 

 tion and especially a direct role in the activation of the egg has 

 centered about the following considerations : (a) the universality 

 of occurrence of fertilizin among metazoa, (b) the source of 

 fertilizin, (c) the effect of removal and addition of fertilizin on 

 the fertilizability of the egg, and ( d ) the effect of fertilizin on the 

 fertilizing capacity of sperm. 



The evidence with regard to these points has been reviewed 

 in detail by Tyler (1941, 1948a, 1955). Therefore it will suffice 

 here to summarize this information and emphasize the most 

 recent work. 



Occurrence of Fei'tilizin. If fertilizin has a fundamental role 

 in fertilization, it might be expected to occur widely if not uni- 

 versally. Lillie (1919) and Just (1930) believed this to be the 

 true, although they demonstrated agglutination of sperm by egg 

 water in only a limited number of forms. Subsequently, others 

 have added to the Hst (Tyler, 1948a; Bielig and von Medem, 

 1949) so that positive cases are now known in four of the major 

 phyla (molluscs, annelids, echinoderms, chordates). However, 

 the fact remains that the number of species included is small. 



Nevertheless, the list is being extended. This extension involves 

 both the discovery of orthodox egg water agglutination of sperm 

 as new species are examined and the development of special 

 methods for detecting fertilizin in egg waters that ordinarily fail 

 to agglutinate homologous sperm. Two such methods have been 

 employed successfully. The first is based on the premise that fer- 



