No. 3-] MORPHOLOGY OF THE STENTORS. 497 



writers that, except in a very few instances {e.g., Opalina), 

 multiplicity of meganuclei does not obtain in this group. Even 

 where the meganuclear substance has every appearance of being 

 broken up into an immense number of separate elements, as 

 in Urostyla (Bergh, '89), Holosticha (Gruber, '88), HolopJuya 

 (Maupas, '83), and other forms, it is maintained by Balbiani, 

 Biitschli, and others that the apparently separate elements are 

 all nodes of an immensely long and much-convoluted mega- 

 nucleus, the commissures of which are so exceedingly fine as to 

 escape observation. I am, however, of the opinion that 

 complete meganuclear division does occur among the Ciliata 

 independently of fission. Among the Stentors, commissures 

 are comparatively thick and conspicuous, so that there is never 

 the least difficulty in making them out. Furthermore, the node 

 is tapered more or less where it is produced into the commissure 

 (Fig. 19). But in S. pyrifonnis and 5. ignetts there is neither 

 any trace of commissures nor of a tapering of the meganuclei 

 (Figs. 3, 23). As long as the daughter-nuclei remain in 

 connection, the constricted part is perfectly distinct, (Fig. 24) 

 and absolutely no evidence has been found of its being drawn 

 out into an exceedingly slender commissure. 



Perhaps the strongest evidence that can be adduced in favor 

 of the presence of invisible commissures joining the mega- 

 nuclear elements, is the consolidation of all the nodes into a 

 single mass at time of fission. It appears to me extremely 

 doubtful whether this takes place when the nuclear elements 

 are wholly separate. As all observations on the condensation 

 of unquestionably moniliform nuclei show, the concentration 

 takes place by a widening out of the commissures ; and from 

 watching the changes in the living meganucleus of ^. cceruleiis, 

 I have been impressed by the fact that the nuclear membrane 

 effectually prevents coalescence of separate nuclei, even when 

 they are strongly pressed together (see p. 514). It would, 

 therefore, be very interesting to observe the behavior of the 

 meganuclei in S. igneiis or S. pyriformis at time of fission. 

 This unfortunately I have not been able to do, owing to the 

 great rarity of fission in these forms when kept in confine- 

 ment. 



