14 BULLETIX 120, UNITED STATES NATIONAL MUSEUM. 



time, evidently usually for days, probably for many days, in a sort 

 of mctaphasc condition, the two daughter nuclei being still con- 

 nected by a long thread, and the reticulate condition of the chro- 

 matin being not yet fully assumed. This is the typical condition for 

 this species. 



Mention of a skein stage (fig 4, b) preceding the equatorial plate 

 stage was omitted. It is often found and is sometimes very clear, 

 but after prolonged study of thousands of dividing nuclei of this 

 and other species I have the impression that a definite skein^ is 

 sometimes not foraied and that the equatorial migration of cliro- 

 rnatin masses and their concomitant fusion or division to form the 

 proper number may occur directly after the reticulate condition with 

 no clear skein condition intervening. A good many nuclei are in a 

 condition which seems best explained l)y such a direct transition 

 from reticulum to equatorial plate. To determine this point the 

 sequence of mitotic phenomena should be observel in the living 

 nuclei, and this has not been done. Mitosis has been repeatedly 

 studied in the living nucleus and the number and something of tha 

 condition of the chromosomes observed, even the chromatin fibers 

 being quite visible, but the succession of events has not been ob- 

 served. The abnormal conditions outside the host, while apparently 

 stimulating the Opalinids to enter upon division, at the same time 

 usually prevent its completion. Either the mitotic phenomena nor- 

 mally proceed very gradually, or they do so as a result of the 

 abnormal environment outside the host. At any rate the phenomena 

 do not go forward with sufficient speed to allow observation of their 

 sequence when the animals are pressed by the cover glass and held 

 immovable for study with immersion objectives. 



Longitudinal splitting of the chromatin masses does not seem to 

 occur in the equatorial plate. The division there is a transverse 

 pinching apart into two portions. The resultant daughter masses 

 remain connected in pairs across the equator of the nucleus by means 

 of persistent chromatin threads (see figs. 28, d, p. 53, 49, h, p. 80, and 

 86, &, p. 121). One readily sees that the daughter masses of a single 

 pair are very closely similar. In any one anaphase group the several 

 daughter chromatin masses differ from one another with charac- 

 teristic differences of size, form, and behavior (see fig. 86, h, p. 121), 

 and these constant differences are observed in comparing different 

 nuclei in different animals. There is therefore a clear individuality 

 of these chromatin masses which is characteristic in detail of each of 

 the eight components of the group. But though longitudinal split- 

 ting of the chromosomes does not occur in the equatorial plate, one 

 finds often in the telophase stages that the chromatin masses show a 

 vague yet evident double appearance, two darker-stained lateral 



