220 V. A. DOGIEL 



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 Cihata where 

 the members of a pair show very marked differences, which may 

 have a relation to sex. 



The species of ciliate which I have studied belongs to the 

 genus Ophryoscolex (order, Oligotricha : family, Ophryo- 

 scolecidae). The representatives of this family lead a parasitic 

 mode of life in the stomach or the intestine of different 

 Ungulata. Ophryoscolex janus, the form described, is 

 a new species, found in the stomach of African antelopes, 

 Bub a lis cokei and Madoqua sp. The antelopes were 

 shot by me during my expedition to British East Africa in 

 1914, on the shores of Lake Naivasha. 



In order to make my description more comprehensible 

 I am obliged to describe in some detail the morphology of 

 0. janus. The ordinary or, as we shall call them, neuter 

 individuals of 0. janus have the following structure. 

 The body (PI. 17, fig. 1) is oblong, and approximately cylindrical, 

 its posterior half being a little wider than the anterior one. 

 The anterior end of the body bears the mouth, lying on the 

 top of the oral cone : the posterior end is provided with a long 

 and slender terminal spine. The ciliary apparatus consists of 

 an adoral zone (Adz) and a dorsal crescent (Dz) of mem- 

 branellae. This crescent in 0. janus is removed very far 

 backwards, lying a little behind the middle of the body. The 

 mouth leads into a long pharynx, with a very complicated 

 structure. It begins with a rather narrow oral cavity, which 

 farther backwards widens into the pharynx proper ; the 

 pharynx follows the right side of the body to its hinder end, 

 growing gradually narrower backwards. Close to the posterior 

 end of the body the pharynx communicates with the endoplasm. 

 This latter is so well defined by a thin continuous membrane that 

 we can term it (in agreement with other authors) the mid-gut. 

 The mid-gut sends out anteriorly a long conjugation outgrowth, 

 which lies parallel to the pharynx and during conjugation 

 serves as a bridge for the migration of the male pronucleus. 



