88 bulletin: museum of comparative zoology. 



of the division process and concern ourselves chiefly with the fate of 

 the chromosomes after their division and separation has been accom- 

 phshed. 



In my account of the accessory chromosome, I have already men- 

 tioned the formation of sacs or vesicles in the telophases of the sperma- 

 togonia. In an early telophase, such as is shown in figure 5 (Plate 1), 

 the chromosomes are clumped together in a rather compact mass at 

 the pole of the spindle. But the distal tips of the larger chromosomes 

 may be seen projecting in various directions. Following the clumped 

 condition, stages occur during which the chromosomes begin to ex- 

 pand and to separate from one another. iVt the same time there is 

 developed about each chromosome a hyaline area, at first small in 

 extent, but gradually enlarging as the chromosomes continue to ex- 

 pand. These conditions are shown in figures 6-9. Figure 6 is a side 

 view and figure 7 a transverse (optical) section of the same stage. 

 Figures 8 and 9 are likewise side view and optical section, respectively, 

 of a later stage. At this later stage it will be seen that a membrane 

 has been formed at the boundary between the hyaline area and the 

 cytoplasm. We are therefore probably dealing with sacs or vesicles 

 similar to those described by Sutton ('00) for Brachystola. 



What is the origin of these sacs? Does the hyaline region as it 

 first appears represent material from the cytoplasm, or from the chro- 

 mosomes, or is it an artifact resulting from the contraction of the 

 chromatin under the influence of the fixative? That it is not an arti- 

 fact, will be apparent, I believe, from the following considerations: — 



(1) The chromosomes themselves, at the stages shown in figures 6 and 

 7, are larger than in the earlier stages represented in figures 3 and 4. 



(2) The chromosomes continue to expand and the vesicles expand still 

 more rapidly, as will be seen from the later stages (fig. 8 and 9). (3) 

 The hyaline region as seen in figures 6 and 7 appears more highly 

 refractive than the cytoplasm which would not be the case if it were a 

 space produced by shrinkage of the chromatin. 



A comparison of the conditions shown in figures G and 7 with those 

 shown in figures 10 and 12 will, I believe, show that the expansion of 

 the vesicles has been at the expense of the cytoplasm. The relative 

 volume of the space within the vesicle as compared with the volume of 

 the cytoplasm, is much less in these earlier stages (fig. 6 and 7) than 

 in the later stages (fig. 10 and 11). Further, it will be seen that the 

 expansion of the vesicles is accompanied by: — (1) an increase in the 

 size of the cell-body, (2) a diffusion of the chromatin into a kind of 

 reticulum within the space of each sac, (3) the breaking down of the 



