EUPLOTES WORCESTERI: II. 323 



It is difficult to determine the number of chromosomes accurately, in 

 spite of their small number. The usual number appears to be six or 

 seven, although I have counted eight on a few occasions; but at other 

 times I have been able to distingiiish only four, or five. When the 

 spindle is first fully formed the chromosomes are thickest at their 

 middles, tapering slightly toward the ends. As division progresses the 

 chromatin passes away from the middle of the chromosome toward the 

 end, until finally the central portion is reduced to an extremely fine fibril 

 connecting the considerably enlarged ends. (Plate VI, figaire 19.) This 

 still stains with chromatin stains, so does not seem to correspond exactly 

 to the ordinar}' linin fibril. After the chromatin has become massed at 

 the poles, the spindle elongates very considerably, the fibrils still joining 

 pole to pole. 



It will be seen by a comparison of figures 8, 10, 13, and 14, Plate V, 

 that metaphase and anaphase occur with great rapidity, since there is 

 almost no difference in the condition of the nieganuclei of figures 8, 10, 

 and 13. .Stages of the micronucleus like those shown in figures 13, Plate 

 V, and 31, Plate VI, are also extremely rare. These are the only 

 anaphase and telophase stages I have been able to find in an examination 

 of many hundreds of dividing individuals. The shape of each daughter 

 micronucleus in figure 13, Plate V, shows plainly that the final step in 

 division is a rapid separation of the jDoles of the spindle, while the sf)indle 

 fibers remain unbroken for a considerable time. A break finally occurs 

 at the center of the spindle and the fibers of each half of the spindle are 

 withdrawn into their respective nuclei. A clear space is found around 

 the micronucleus in nearly every preparation of dividing Euplotes. I 

 can not consider this as anything Imt an artifact, caused by slight shrink- 

 age of the distended and fluid-fUled micronucleus. 



The daughter micronuclei separate rapidly after division, quickly com- 

 ing to rest at the points which will be their permanent positions in the 

 daughter bodies. These positions are retained throughout the further 

 processes of division. 



The micronuclei rapidly assume the ordinary resting structure, and to 

 all appearances are perfectly passive during the succeeding, most active 

 phases of division. The short-lived activity of the micronucleus and its 

 succeeding ijassivity are in marked contrast to the activities of the 

 meganucleus and of the body as a whole. The meganucleus, supposedly 

 a vegetative organ, exhibits far more constructive and directive activity 

 than the micronucleus, which is usually considered to be the principal 

 directive agent in division. The formation of chromosomes and their 

 division in the micronucleus is a simple matter compared with the com- 

 plex ph3'sical and chemical changes occurring in the chromatin of the 

 meganucleus. The activities of the meganucleus begin with or before 

 the first intimation of other division processes, and continue imtil after 



