24 EGG AND SPERM SUBSTANCES 



recent of these (Felix, 1955) may meet a similar fate. Neverthe- 

 less, it should be recalled that paramecia killed by various agents 

 including formalin will specifically activate paramecia of oppo- 

 site mating type (Metz, 1947, 1954a). Therefore this direct ap- 

 proach to the problem may still hold promise even for the more 

 orthodox material. 



Although these efforts with metazoa appear to have failed in 

 their primary objective, they and related studies have shown that 

 a number of interesting substances may be obtained from both 

 eggs and sperm. Certain of these agents clearly perform a neces- 

 sary role in fertilization and the nature of some others suggests 

 that they too may eventually be assigned a definite if not essen- 

 tial function in fertilization. 



Serious study of such agents began with Frank R. Lillie's in- 

 vestigation of the sperm isoagglutinin, fertilizin, which he 

 obtained from the eggs of the sea urchin Arbacia and the annelid 

 Nereis. Lillie's (1912, 1913b, 1914, 1919) studies produced the 

 only comprehensive, though now outmoded, theory of fertiliza- 

 tion, namely the Fertilizin Theory. Publication of the Fertilizin 

 Theory stimulated a very considerable series of studies during 

 the following decade. Interest then lagged until the late nineteen 

 thirties when it was revived largely by Hartmann and his associ- 

 ates in Germany and by Tyler in America. This interest has stead- 

 ily increased but with it has come much conflicting data and 

 many divergent statements, owing in part at least to differences 

 in experimental material. Unfortunately, several of these areas of 

 disagreement have not been resolved satisfactorily in the litera- 

 ture. These will receive particular attention here. Some of the 

 well-established aspects of the subject will be treated in less de- 

 taij for they have been discussed in several reviews (Bielig and 

 von Medem, 1949; Tyler, 1948a, 1949, 1955; Runnstrom, 1949a,b, 

 1952; Rothschild, 1951a,b). 



Classification of Sex Substances 



Fertilization presupposes a ripening of the parent animals and 

 an appropriate release of the gametes. These processes have been 

 found to be controlled in many instances by environmental con- 



