32 EGG AND SPERM SUBSTANCES 



tion between fertilizin and antifertilizin is further considered to 

 result from interaction of specific reactive groups or sites of fer- 

 tilizin with other reactive groups on the sperm surface (anti- 

 fertilizin). The reactive groups of fertilizin and antifertilizin are 

 endowed with a high order of configurational complementariness 

 and the specificity of fertilizin agglutination resides in the specific 

 "lock and key" nature of this complementary relationship. Finally, 



Fig. 1. (a) Agglutination of sperm by interaction of multivalent ferti- 

 lizin with antifertilizin of sperm surface, (b) Multivalent fertilizin split into 

 univalent fragments, (c) Failure of sperm to agglutinate with multivalent 

 fertilizin following saturation with univalent fertilizin. (From Rothschild, 

 1951b.) 



the agglutinating fertilizin molecule is considered to be multiva- 

 lent with respect to its specific reactive groups. Agglutination 

 results when several sperms are linked together by fertilizin 

 molecules. These relations are illustrated schematically in Fig. 1. 

 In most groups of organisms where it has been reported, fer- 

 tilizin agglutination presents an orthodox antigen-antibody type 

 reaction. In the echinoderms, however, certain interesting excep- 

 tional features have been reported. These include spontaneous 



