l6o GRACE MEDES. 



mosomes and the astral rays have disappeared. As the telo- 

 phase advances, the chromosomes become more granular, stain 

 less deeply, and appear in the next stage (Fig. 3), as a mass of 

 dense granular threads. Already the growth period has begun, 

 and a slight increase in the size of the cell may be observed. 

 At this period one other important feature may be mentioned. 

 This has to do with that peculiar structure, first clearly recog- 

 nized by McClung ('99) as a chromosome, and described by him 

 under the name of accessory chromosome. This element may 

 be distinguished from the other chromosomes at this period by 

 certain peculiarities in its form and behavior. During the telo- 

 phase, while the other chromosomes have been lengthening into 

 diffuse, flaky segments, this structure has remained unaltered 

 and still retains the stain with the tenacity of a chromosome 

 during the metaphase. As is to be expected from its composi- 

 tion, its reaction to stains is quite different from that of the ordi- 

 nary chromosomes. When stained by Flemming's three-color- 

 method, this element takes the saffranin, whereas the others 

 retain the gentian violet. 



During the period immediately following, the cell gradually 

 increases in size, and the reconstruction of the nuclear membrane 

 takes place. By this time (Fig. 4), the cell has increased about 

 one half and the nucleus is considerably larger in proportion 

 than at any other period. The cytoplasm, moreover, stains more 

 lightly and shows scarcely any structure. The chromosomes, 

 immediately after assuming their thread-like shape, lie tangled 

 together in a close heavy mass (Fig. 3), but by the time the 

 nuclear membrane has formed, they begin to spread out through 

 this vesicle and the separate threads may be distinguished (Fig. 

 4). While this is taking place, these threads of chromatin have 

 gradually become more granular and diffuse, and very evidently 

 fewer in number, \vhile the small black body, above pointed out 

 as the accessory chromosome, has apparently become larger. 

 Into the composite structure, hereafter to be called the karyo- 

 sphere (Blackman, '03), the diffuse masses of chromatin gradually 

 accumulate (Figs. 5-6) until the nucleus outside of the karyo- 

 sphere is entirely free of chromatin, and only the linin net-work 

 is to be seen. 



