SEX IN INFUSORIA 221 



A short tube-like rectum ends with a circular anal aperture 

 at the base of the terminal spine. As a characteristic feature 

 of 0. janus we can mention the very strong development of 

 the inner skeleton. It is represented by a thin plate (PI. 17, 

 fig. 1, shp) of alveolar structure, lying under the tough super- 

 ficial cuticle of the body. Anteriorly the skeletal plate surrounds 

 the body, forming under the cuticle a sort of stiff collar, whose 

 opposite ends meet on the dorsal side of the animal to form 

 a suture-line. In the posterior half of 0. janus the right 

 side of the plate retains its superficial subcuticular position, 

 while the left one separates from the cuticle and dips into the 

 interior, forming a wing-like outgrowth, which surrounds and 

 supports the hinder part of the pharynx. There are special 

 myonemes, described in other Ophryoscolecidae by Sharp 

 and Braune, closely connected with the pharynx. They 

 form a continuous thin layer on the sides of the pharynx 

 supported by the skeletal plate, to whose inner surface the 

 myonemes are attached. The myonemes begin at the posterior 

 end of the pharynx, pass forwards, and, after reaching the 

 anterior third of the body, detach themselves from the skeletal 

 plate and converge to the centre of the body, following the 

 wall of the pharynx. In so doing this muscular layer forms 

 a sort of oblique diaphragm (fig. 1, D) which is concerned with 

 the ingestion of food particles. 



The strong development of the skeletal collar removes the 

 nucleus and the contractile vacuoles far backwards. The 

 macronucleus is usually lemon-shaped and lies on the right 

 side of the animal, somewhat nearer to the ventral surface of 

 it than to the dorsal one ; in a cup-like depression of the macro- 

 nucleus the small ball-shaped micronucleus is situated (PI. 17, 

 fig. 1, Mi). A little dorsally from the macronucleus lie both 

 the contractile vacuoles (Fj, V2), the anterior being con- 

 siderably larger than the posterior one. 



Besides the neuter individuals I met (in both the antelopes 

 investigated) with conjugating pairs of 0. janus. The great 

 majority of pairs proved, to my great astonishment, to consist 

 of individuals widely different in dimensions and several other 



