119 



The next stage (Fig. 3) shows the filaments much short- 

 ened, and very evident. They color also much more uni- 

 formly and lie in the colorless nuclear cavity, which is still sepa- 

 rated from the cell-plasm by an evident membrane. The latter 

 soon disappears, however, leaving the short, thick segments free 

 in the center of the cell (Figs. 4, 5). Podophylliun is es- 

 pecially favorable for showing this stage and those immediately 

 following, on account of the small number (about ten) of the nu- 

 clear segments. These arrange themselves in the form of a disc 

 (nuclear-plate) across the center of the cell (Figs. 4-7K.), and each 

 segment splits longitudinally into two similar daughter-segments, 

 which are usually more or less distinctly bent, often being V- 

 shaped (Fig. 6). Sometimes this division of the segments 

 seems to begin before the disappearance of the nuclear membrane 



(See Fig. 3). 



When the nuclear-plate is complete there may be seen, though 

 this is often difficult in acetic acid preparations, fine hues 

 (Fig. 7F.) converging near the poles of the cell, so as to form a 

 spindle-shaped figure with the nuclear-plate at the equator. The 

 whole constitutes the " nuclear-spindle," and the fibers of which 

 it is composed, the " spindle-fibers " {Spindelfasern of the Ger- 

 man authors). The spindle-fibers probably correspond in num- 

 ber to the segments of the nuclear-plate, but this is difficult to 

 prove. For studying this point, alcoholic material is preferable. 

 . As soon as the nuclear-spindle is completed the daughter seg- 

 ments separate and travel along the spindle-fibers to the poles 

 of the spindle, (Figs. 8, 9). When viewed from the poles 

 they often show a very regular, stellate arrangement, the V- 

 shaped segments being arranged in a circle with the free ends 



outward. 



As the two sets of segments separate, fine lines may be de- 

 tected connecting the young nuclei (PI. CIII. Figs. 8- 1 2 V.) These 

 " connecting threads " ( Verbindungsfaden) are much more numer- 

 ous than the spindle-fibers. After reaching the poles, the daugh- 

 ter nuclei pass through much the same phases, but in reverse 

 order, that preceded the division of the primary nucleus (see 

 figs. 10-13). About the time that the nuclear membrane 

 becomes evident, or sometimes a little earlier, a plate composed 



