222 V. A. DOGIEL 



morphological features — differing in several points not only from 

 one another but also from the neuters. Let us call them micro- 

 and macroconjugants, without giving to these names 

 the significance of sexual differentiation. The macroconjugant 

 (PI. 17, fig. 2, left-hand individual) differs less than the micro- 

 conjugant from the neuter individuals. The macroconjugants 

 are individuals 82-112 /x long and 42-55 ij. broad (at the level 

 of the macronucleus), the great bulk of them measuring from 

 90 fx to 100 iJL. The posterior part of the body is somewhat 

 shortened and inflated in comparison with the neuters. The 

 most prominent differences from the neuter individuals, 

 however, consist in the lack of the hind contractile vacuole 

 and in the character of the terminal spine. Long and slender 

 in neuters, the spine is short and thick in the macroconjugants, 

 being about one-third as long as in the neuter specimens. 



The microconjugants are even more strongly modified 

 (PI. 17, fig. 2, right-hand individual). They are 60-75 /x long 

 and 20-5 // broad. It is easy to see (PI. 17, figs, 2 and 12) that 

 the general aspect of the body becomes quite different from 

 that of the macroconjugants, the body being long, slender, 

 and somewhat vermiform. The difference will appear still 

 greater if we compare the respective volumes of both types of 

 individual. Thus for a microconjugant of 75 /x x 25 /^ we shall 

 have an approximate volume of 34,000 cubic microns, while 

 a macroconjugant of 90/xx45;u will give a total of 137,000 

 cubic microns — that is, about four times the volume of a micro- 

 conjugant. 



Notwithstanding its small size the microconjugant possesses 

 a long and slender terminal spine, of just the same length as 

 that of the neuter specimens. The skeletal plate, so charac- 

 teristic of 0. janus, is wholly lacking. This absence of the 

 endoskeletal plate does not remain without influence on several 

 other internal characters of the microconjugant. The outline 

 of the anterior half of the body becomes folded and wrinkled, 

 while in the macroconjugant it appears smooth and even. 

 The pharyngeal myonemes, having lost their line of insertion, 

 hang loosely back and form a sort of long muscular cone 



