On Sexual Differentiation In The Infusoria

Abstract

ABSTRACT The object of this preliminary note is to describe a very curious type of conjugation which may throw light 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),x with good reason, points out that in cases of typical conjugation both the conjugants are to be looked on as hermaphrodites which are performing cross-fertilization. Only in Vorticellids 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 Chilo don 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 sexuality ‘in Paramecium proved to be erroneous (Jennings and Lashley), and need no further mention. But in this paper I propose to describe a case of conjugation in the Ciliata where the members of a pair show very marked differences, which may have a relation to sex.