250 University of California Publications in Zoologij [Vol. 16 



in size and continues to diminish until only the slender central spindle 

 is left (pi. 20, fig. 52). In the dumb-bell stage this connection between 

 the polar masses is quite evidently on the outside of the s[)iudle, but 

 in the later stages it is within the spindle in an axial position. The 

 stage at which this change of position takes place seems to be that in 

 which there is a separation of the two chromatic polar masses (pi. 18, 

 fig. 9 ; pi. 20, fig. 52) with only the central spindle connecting them. 



Part of the plastin of the karyosome may project out beyond the 

 chromatic portion to the nuclear membrane as a polar cap in the meta- 

 phase. This projection, conical in shape, with the base resting on the 

 chromatic polar mass and the point to the membrane, is variable in its 

 appearance and relative size. It is sometimes very evident (pi. 18, figs. 

 6, 7, 10), sometimes only barely visible (pi. 18, fig. 9: pi. 20. fig. 48) 

 and sometimes completely obscured, being entirely covered by the 

 chromatin of the polar mass (pi. 18, fig. 11). While this last condition 

 may be found occasionally in the early stages of division beginning 

 with late prophase, in which case the polar mass is conical in shape, 

 it is always found in the late anaphase and the telophase (pi. 18, figs. 8, 

 12-15; pi. 20, figs. 37, 51). Here the polar mass is flattened at the 

 end instead of coming to a point as it does in the earlier stages. Like- 

 wise, there are no polar caps in the reorganization stages of the nucleus 

 (pi. 19, figs. 17,25). 



The chromosomes, the formation of which will be discussed later, 

 behave in various ways after the metaphase. They may be pulled to 

 the pole as separate entities (pi. 18, fig. 13) gradually fusing in the 

 later stages, they may become separated into granules as they are 

 pulled apart (pi. 18, fig. 10), or they may early become more or less 

 fused (pi. 18, fig. 6). However, they finally fuse into a mass which is 

 more or less closely connected with the chromatic polar mass (pi. 18, 

 fig. 15). This connection becomes closer until fusion is finally com- 

 plete in the resting nucleus (pi. 19, fig. 19 ; pi. 20, fig. 43) . The region 

 between the chromosome mass and the polar ma.ss, made up of the 

 remains of the spindle fibers, becomes the plastin-like center of the 

 new karyosome (pi. 20, figs. 43, 53). 



In the karyosomes of preparations which have been nearly com- 

 pletely destained. a granule much darker than its surroundings may 

 be distinguished (pi. 20, fig. 59). Also, in some elongated karyosom&s, 

 which are not very deeply stained, may be foimd two granules, the 

 centrioles, with a slender connection, the central spindle (pi. 20. fig. 

 62). This last condition may also be di.stingui.shed in late prophase 



