288 SEX IN MICROORGANISMS 



the hypotrich Eiiplotes patella. In this form Kimball (1942) has 

 shown that the fluid from certain clones will induce animals of certain 

 other clones to conjugate. The most intensively studied agent of this 

 sort from metazoan gametes is the fertilizin obtained from eggs. In 

 its most spectacular form such fertilizin specifically agglutinates the 

 sperm of the species. 



Although freely diffusible, water-soluble sex substances of this 

 sort occur in the most diverse animal groups (Protozoa and Verta- 

 brata), they have not been demonstrated universally in either pro- 

 tozoa or metazoa (see Tyler, 1948, concerning metazoa). In the 

 demonstrable absence of such agents, specific sexual reactions, either 

 between protozoa or metazoan gametes, may be attributed again to 

 specific sex substances. However, in such cases the agents must be in- 

 soluble in the fluid medium, firmly bound to the cell, or both. It will 

 be seen in the account to follow that sex substances in Faramecium 

 are exclusively of this type, and on proper analysis this condition may 

 be expected to be found widely among metazoa and protozoa alike. 



FERTILIZATION IN PARAMECIUM 



Normal Sexual Phenomena 



Two sexual processes occur normally in Farameciwn: conjuga- 

 tion and autogamy. The essentials of these are presented here as back- 

 ground for the analysis to follow. For a more detailed account of 

 normal conjugation and autogamy and a thorough treatment of the 

 literature, the reader should consult Sonneborn's (1947) excellent 

 review. 



Conjugation. Conjugation in Paramecium involves several types 

 of union between mates and a variety of internal changes in these 

 animals. The first step in conjugation is the initial adhesion. Under 

 suitable conditions this takes the form of the striking mating reaction 

 described first by Sonneborn (1937). Dozens, even hundreds, of 

 animals stick together to form large masses or agglutinates. After 

 some time these mating reaction clumps break down, releasing mating 

 pairs and single animals. Animals in mating pairs are united at first 

 only at the holdfast region (Jennings, 1911; Wichterman, 1940; Hert- 

 wig, 1889; Metz, 1947) near their anterior ends (Fig. la). This hold- 

 fast union is firmer and more intimate than the mating reaction union. 



