THE OPALIXID CILIATE INFUSORIANS. 15 



regions having a paler strip between them (fig. 4, /). The three 

 bands thus formed in each chromatin mass lie lengthwise in the mass. 

 I am not sure whether the appearance indicates a true double con- 

 dition of the chromatin masses at this stage, or is due to the presence 

 of an achromatic core in the axis of the chromatin mass. The latter 

 interpretation is suggested by the fact that usually all the chromatin 

 masses in a nucleus in this phase show this appearance of splitting 

 when seen from one point of view. If it were true splitting, some of 

 them would naturally be seen from such an angle as to obscure their 

 double character. Observation of mitoses of some other protozoa 

 shows that splitting of the chromosomes in the metaphase stages is 

 not exceptional. 



The telophase may be said to be passed when the thread between 

 the two nuclei .breaks and the nuclei become more spherical. There 

 follows at this time an apparently brief reticulate stage, with mostly 

 small chromatin masses scattered over the periphery of the nucleus, 

 beneath the caryotheca, these masses being connected by delicate 

 branching fibers of chromatin. Apparently the telophase passes into 

 the reticulate condition by the further fragmenting of the chromatin 

 masses and their sending out during the process numerous filose and 

 branching pseudopodia to form the fibers of the chromatin net. 



As the chromatin masses of the reticulate stage pass into the skein 

 of the following stage, some of the fibrillae of the reticulum decrease 

 in size and others become emphasized. This process continues until 

 the outer chromatin spindle is formed. Apparently the lateral 

 branches are drawn in, as filose pseudopodia might be withdrawn, and 

 the main threads, running longitudinally, are thus increased in size. 

 Even at the time when the outer chromatin spindle is most fully 

 developed as a spindle, its fibers still show some branching. 



In the absence of a centrosome during mitosis, as at all other times, 

 the fibers of the outer chromatin spindle are attached to the nuclear 

 membrane at its two poles. This seems to be a permanent attach- 

 ment. When the nucleus divides at the equator, its membrane pinches 

 down upon the persistent spindle fibers and holds them permanently 

 fastened (see Protoopalina mitotica, fig. 48, e, p. 78). The fibers 

 seem to be a part of the persistent chromatin complex, and the chro- 

 matin seems to be autonomous in its movements and not to be acted 

 upon by any outside agents, such as contractile fibrillae from centro- 

 somes, to pull the chromosomes through their quadrille. 



Thus far in our description of mitosis we have referred only to the 

 chromatin masses and their chromatin fibrillae, forming the outer 

 chromatin reticulum and the outer spindle. There is another set of 

 chromatin structures lying more internal than these (fig. 4, a. See 

 also fig. 85, b, p. 120) , There are chromatin granules, appearing some- 



