18 Art. 6.— I. Ikeda and Y. Ozald : 



both the upper and the lower individuals become provided with a 

 mouth and a low oral ciliary spire. At this stage the meganucleus 

 is already constricted into two of equal size and of quite a similar 

 structure. The chromatin granules now leave the surface of tlie 

 central plasmosomic mass and adhere to the inner surface of the 

 nuclear membrane, exactly as they do in the individuals arising 

 from the first fission after conjugation (see fig. 17). 



From the foregoing, it will be clear that, in the present 

 species, there may be distinguished two types of meganuclear 

 division, namely, the trinal and the binary. The former takes 

 place in the two successive fissions following the conjugation, the 

 latter in the ordinary binary fission. We are of the opinion that 

 the first binary fissions of the ex-conjugant are but a modification 

 of trinal fission. This seems plain, not only from the trinal divison 

 actually undergone by the ex-conjugant meganucleus, but also from 

 the presence within the meganucleus of the three quarter-parts of 

 the synkarion chromatin. This mode of fission of the ex-conjugant 

 may be regarded as a process by which asexual reproduction, and 

 at the same time, a regulatory distribution of the meganuclear 

 and micronuclear substances are accomplished. In this sense th's 

 modified trinal fission in question may be called the regulatory 

 fission. 



We are inclined to think that similar sorts of the two types 

 of meganuclear division and of fission possibly exist also in the 

 species studied by Stevens, to which the present species is closely 

 related in many other respects. 



IV. Fragmentation of the meganucleus and its 

 physiological significance. 



In Boveria labialis, the occurrence of a single meganucleus 

 and a single raicronucleus is to be looked upon as the normal 



