70 bulletin: museum of comparative zoology. 



varying lengths (Figs. 7, 8). These rods at first have a ragged outline 

 and often show a more or less distinct longitudinal split. Frequently 

 the ends of the rods can be traced out into the sacculations of the 

 nuclear wall. In sections through one side of the nucleus (Figs. 9, 10) 

 the rods often appear to lie in distinct compartments separated from 

 each other by a thin membrane. This, however, is probably not the 

 case. Apparently these compartments are simply outpocketings or 

 sacculations of a common nuclear membrane which have been cut in 

 such a way as to give the appearance of distinct vesicles. The chro- 

 matic rods continue to shorten and thicken and become more compact, 

 each one forming a single rod-shaped chromosome. Shortly after 

 the chromatic rods appear in the nucleus, there can be distinguished 

 in the cytoplasm close to the nuclear membrane two small but well 

 defined asters (Figs. 7, 8). At the center of each aster there is usually 

 a very minute deeply staining granule, which is e\idently the centro- 

 some. It is, however, doubtful if these centrosomes are present 

 when the asters first appear, for, in a number of cases where the asters 

 were barely distinguishable, I have been unable to find any centro- 

 somes at the center. The centrosomes when they first appear are 

 very minute, but increase rapidly in size. The asters always make 

 their appearance on that side of the nucleus which is directed towards 

 the interzonal body, and is much flattened or even concave. Following 

 Montgomery (:00, p. 294) I shall call this the distal pole, the opposite 

 one being the central pole of the cell. 



Whether the centrosomes retain their individuality during the 

 resting stage, it is impossible to say, although the manner of their 

 appearance during the prophase would argue against such an inter- 

 pretation. If they do exist as morphological entities in the resting 

 cell, they must be so minute as to be indistinguishable. Since in the 

 prophase the centrosomes reappear at the distal pole while during the 

 telophase of the preceding division they were at the central pole, it is 

 obvious that their persistence during the resting stage involves their 

 migration from the central to the distal pole through, or around the 

 nucleus. 



When the two asters first appear they are always some distance 

 apart, and in no case have I been able to distinguish a central spindle 

 or centrodesmus between them at this stage. However, they may be 

 connected to each other by the astral rays which extend out for a 

 considerable distance in all directions. Surrounding the asters is a 

 mass of mitochondrion from which the astral rays appear to be formed, 

 but it is impossible to determine this with any certainty. As the 



