On Sexual Differentiation in the Infusoria. 



By 

 Prof. V. A. Dogiel, 



Zootomical Laboratory, University of Petrograd. 



With Plate 17 and 1 Text-figure. 



The object of this preliminary note is to describe a very 

 curious type of conjugation which may throw hght on the 

 process of sexual differentiation in the Infusoria — a type leading 

 from conjugation between two hermaphrodite individuals to 

 copulation between male and female specimens. In his very 

 lucid account of the genetics of the Ciliata, C. Dobell (1914),^ 

 with good reason, points out that in cases of typical conjuga- 

 tion both the conjugants are to be looked on as herma- 

 phrodites which are performing cross-fertilization. Only in 

 VorticelUds there are males and females, and the sexual process 

 changes to copulation, while the dwarf-like male perishes after 

 fertilizing the larger female. In other Ciliata there are no well- 

 proved cases of sexual differentiation of the conjugants, although 

 some hints at it are to be found in the works of Cull, Doflein, 

 and Enriques. Doflein states that the conjugants of the same 

 pair in Paramecium putrinum differ very much in size, 

 a feature which he is ready to attribute to sexual differentiation. 

 Enriques relates of Chilodon that the conjugants, which 

 are very much alike at the beginning of conjugation, become 

 differentiated into a longer and a shorter one during the process 

 of conjugation. The meaning of such conjugants — termed by 

 Enriques ' male and female hemisexes ' — remains obscure, as 

 also the extensive discussion of the author on the subject of 

 sexual differentiation. The observations of Cull on ' incipient 



^ ' Journ. of Genetics,' vol. iv, p. 131, 1914. 



