1918] Yocum: The Neuromotor Apparatus of Euplotes Patella 367 



apparatus were connected with the nucleus, changes should be noted 

 in it comparable with those occurring in the nucleus. A consideration 

 of the behavior of the neuromotor apparatus during cell division will 

 be taken up later. 



BEHAVIOR OF ORGANS AT BINARY FISSION 

 Division of the Micronucleus 



The first indication of division in the micronucleus is its migration 

 from its position in the indentation of the macronucleus to the left 

 side of the macronucleus, where it enlarges (pi. 15, fig. 14) to two or 

 three times its original size. In the resting condition and prophase it 

 is very difficult to make out the arrangement of the chromatin in the 

 micronucleus due to its compact condition. Occasionally there is 

 some indication of a diffuse spireme formation. Griffin (1910) de- 

 scribes a spireme formation in E. worcesteri and in all probability 

 such a change occurs in the nucleus of E. patella. After enlarging 

 somewhat the nucleus assumes a spindle form with the chromatin 

 broken into chromosomes which lie lengthwise on the spindle. The 

 number of these chromatin bodies is small, and while I have not been 

 able to make many conclusively satisfactory counts, it seems that there 

 are six (pi. 15, fig. 15). This corresponds to the number given by 

 Griffin for E. worcesteri. As transverse division is completed the 

 daughter chromosomes become massed at the ends of the elongated 

 spindle. The two poles move apart but remain connected for a time 

 by a deeply staining thread. In such a condition it is almost impos- 

 sible to make out any definite nuclear structure, for the whole drawn- 

 out nucleus appears almost homogeneous and in haematoxylin prepara- 

 tions a dense black. Later the connected thread breaks (pi. 15, fig. 17) 

 and all indications of it are lost. It is probably drawn up into the 

 nucleus, for each daughter micronucleus becomes rounded and is to all 

 appearances like the original micronucleus, but only about two-thirds 

 the original diameter of the parent nucleus. 



The process of division of the micronucleus is evidently quite rapid, 

 for many eases of the beginning of migration can be found as well as 

 of the daughter nuclei, but the cases of actual division are very rarely 

 found. 



The mitotic changes occurring in the micronucleus are accompanied 

 by changes in the macronucleus. The reconstruction of this organelle 

 will be described next. 



