THE OPALIXID CILIATE INFUSORIAXS. 13 



one observes that the chromatin fibres of both sets^^ soon become 

 emphasized in the direction of the elongating axis of the nucleus 

 (see fig. 37, /, p. 64), while their lateral branches seem to be drawn 

 in, at least they become fainter and less numerous, finally almost or 

 wholly disappearing, though their disappearance is in a later mitotic 

 stage, just as the equatorial plate stage is passing into the anaphase. 

 The chromatin masses move toward the equator of the nucleus. 

 The number of the chromatin masses may have been either more or 

 less than eight in the reticulate nucleus according to the degree of 

 concentration of the chromatin into these subcaryothecal chromatin 

 placques. There is no clear equatorial plate but, as the period corre- 

 sponding to this stage approaches, some of these chromatin masses 

 may fuse, others may divide. One or more of them may delay di- 

 viding until the others have passed through the "equatorial plate" 

 and have begun migrating toward the poles of the nucleus. This 

 renders it difficult to count the chromosomes in the "equatorial plate" 

 stage. The chromatin masses then divide, after becoming eight in 

 number, apparently' pinching apart transverseh', and the daughter 

 masses migrate slowly toAvard the poles of the nucleus. This migra- 

 tion is evidently deliberate, for one finds a goodlj' number of the di- 

 viding nuclei in the anaphase condition (fig. 4, d^ e). Just before 

 the daughter chromatin masses reach the poles of the nucleus they 

 may divide, often into unequal moieties. The favorable time, there- 

 fore, for counting the chromosomes is in the middle anaphase period 

 (fig. 4, d), when all the daughter chromosomes, even the laggards, 

 have left the equator and before they ha^ e begun their polar divi- 

 sion. Many dozens of counts of nuclei in this favorable stage have 

 shown the chromatin masses in each daughter group to be eight in 

 number, in the species we are describing. In the telophase (fig 4, e) 

 the chromatin masses lying near the pole of the nucleus send out 

 laterally wide bands of chromatin (shown only in outline in the 

 figure) and thus each one fuses with its two neighboring daughter 

 masses. In this way an irregular ring of chromatin is formed, with 

 irregular protrusions corresponding to the ends of the formerly 

 distinct chromatin masses. Some of the chromatin masses may al- 

 ready have divided and the fragments so formed may or may not be 

 fused into the common ring-shaped group. In Protoopalina satur- 

 nalis (fig. 37, «, p. 64) the polar chromatin ring is less irregular 

 than in P. intestinalis. Later the massive chromatin becomes broken 

 up into more or less numerous bodies of larger or smaller size and 

 by the time the two daughter nuclei have completely separated they 

 may have assumed the reticulate condition. But the daughter nuclei 

 are very slow in completing this process. They remain for a long 



"Those connected with the large, flat chromatin masses and with the chromatin 

 graiiuk's. 



