26 



FERTILIZATION 



proved. It follows that the presence or absence of the necessary 

 number of sulphate groups may not be the only factor which 

 determines the agglutinating powers of fertilizin towards homo- 

 logous spermatozoa. 



Interesting studies have recently been made, notably by Vasseur, 

 on the specificity of the carbohydrate components in fertilizin ob- 

 tained from different sea-urchins. The results are summarised in 

 Table 3, from which it is unfortunately clear that one should not 



TABLE 3 

 Carbohydrates in the egg jelly of certain Echinoderms 



try to make any generalisations about the genus or species speci- 

 ficity of the carbohydrate components of sea-urchin egg jelly. 



Hetero- agglutination. The agglutination of spermatozoa by 

 homologous egg water has several features in common with 

 serological reactions. For example, the reaction is specific. It is 

 true that spermatozoa are also agglutinated by heterologous 

 fertilizin, but this occurs mainly with closely related organisms. 

 The reaction occasionally takes place between distantly related 

 organisms, as in the case of the agglutination of Nereis spermatozoa 

 by Arbacia egg water. F. R. Lillie believed that a distinction could 

 be made between hetero- and iso-agglutination on the grounds 

 that the former does not exhibit the phenomenon of spontaneous 

 reversibility. This view is now known to be incorrect because iso- 

 agglutination may be irreversible, as in the case of the spermatozoa 

 of Megathura cretiulata described by Ty^^^ i^94^^)- Hetero- 

 agglutination can, however, be distinguished from iso-agglutina- 

 tion in other ways. Tyler (1946, 1948) has studied the hetero- 

 agglutination of vertebrate and invertebrate spermatozoa by blood, 

 body fluids and sperm extracts. When fertilizin of one organism. 



