226 



V. A. DOGIEL 



different from the normal one. The anterior end of one con- 

 jugant is sometimes engulfed by the introverted pharynx of 

 its partner (Text-fig. 1), while both the conjugants lie on the 

 same level without forming the characteristic angle of about 

 40 degrees. The long slender terminal spines of both the 

 conjugating individuals indicate that they are neuters. The 

 formation of such pairs might, however, l)e explained in a 

 different way. It might possibly be the result of a fortuitous 

 snapping of one individual at another in its endeavours to 

 engulf food particles ; but such an interpretation does not 

 appear to me very plausible. It might also represent an 

 abortive attempt to conjugate on the part of neuter individuals 



Text-fig. 1. 



A conjoined pair of neuters. 



which are unable to conjugate successfully. In all the 60 per 

 cent, of macroconjugants conjugating inter se with success, 

 the terminal spine is short and thick and the posterior con- 

 tractile vacuole is wanting ; and it is thus evident that these 

 specimens have gone through the preparatory process of 

 progamic fission. 



Such are the most important results of my investigation of 

 the conjugation of 0. j anus. A detailed general discussion 

 of many interesting questions arising therefrom will be given 

 in my full account of conjugation in the Ophryoscolecidae, 

 but I may now venture to draw some conclusions regarding the 

 more striking features of the processes described. 



First of all, the question arises as to which type of conjuga- 

 tion is i)rimary in . j a n u s — the isogamous or the aniso- 

 gamous ? Comparison with the other Ophryoscolecidae and 

 with the great majority of free-living Infusoria seems to 



