334 GARY N. CALKINS 



The transition to the muUinucleate type is by no means abrupt. 

 In the genus Stentor, for example, Johnson ('93) shows that in 

 S.polymorpha the connecting strands (commissures) are relatively 

 thick and conspicuous, while i^i S. pyriformis and in S. igneus 

 no trace of such commissures could be found. In these two species, 

 therefore, the multinucleate condition results from a fragmen- 

 tation of the beaded rod form. A similar fragmentation of a 

 homogeneous rod results in the formation of ten to fourteen 

 nuclei of Uronychia transfuga, but in this case a very delicate 

 connecting membrane can be made out. An extreme case, 

 again, is the multiple fragmentation observed by Lebedew ('08) 

 in Trachelocerca. 



Balbiani, Butschli ('88), Maupas ('83), and others have main- 

 tained that, with few exceptions, in all multinucleate forms, the 

 separate nuclei, or fragments, are held together by similar com- 

 missures and are in effect, therefore, single nuclei. This conclu- 

 sion was based in part upon the obvious connecting strands in 

 many forms and in part upon the fusion, prior to division, of all 

 the parts, or fragments, to form a single homogeneous dividing 

 nucleus. The fact of fusion was regarded as proof of the fact of 

 invisible commissures. 



Against this view^, which is unquestionably too general, are 

 the facts associated with those forms in which the multinucleate 

 condition is a result, not of fragmentation, but of consecutive 

 nuclear division. In most of the binucleate Oxytrichidae the two 

 nuclei arise by equal division, the division taking place just prior 

 to cell division. Here there is, indeed, no fusion, and the effect is 

 that of a single nucleus which has divided precociously for the 

 following cell division. 



G ruber ('87) showed that a similar fusion of entirely discon- 

 nected small nuclei of Holosticha scutellum occurs during prep- 

 aration for division, and that these nuclei arise from the repeated 

 independent divisions of a single nucleus during and immediately 

 subsequent to cell division. Exactly the same phenomenon oc- 

 curs in Uroleptus mobilis; the disconnected nuclei, both after 

 division and after conjugation, arise by repeated consecutive 

 divisions of a single nucleus. 



