14 bulletin: museum of compaeative zoology. 



parently by linin strands, where no chromatin occurs, and the filament 

 is often bent at this point into a V-shaped figure. 



The accessory chromosome apparently takes no part "whatever in this 

 process, but retains all of the characteristics previously noted for it. It 

 is included within the mass of chromatin filaments, or is in very close 

 approximation to this, but undoubtedly receives no addition to its sub- 

 stance except that obtained by ordinary growth. From the foregoing 

 it is evident that the total number of chromosomes is not reduced exactly 

 one half, since the reduction does not affect the accessory chromosome. 



The next change in the condition of the chromatin is represented in 

 Figures 10, 11. Here the synapsis is completed. The chromosomes 

 have withdrawn from the side of the nucleus and have become irreg- 

 ularly arranged throughout the nuclear space, and the accessory chromo- 

 some has assumed the peripheral position which is characteristic of it in 

 all arthropod spermatocytes. It is now readily seen that the chromatic 

 segments are fewer than in the spermatogonia, and by careful counting it 

 is ascertained that they are present in the reduced or spermatocyte num- 

 ber. This stage is as near the spireme stage as any that I have observed 

 in Scolopendra. As I have shown in a previous paper (Blackmail, : 03), 

 however, there is no continuous spireme at this stage, but the chromatin 

 is present in the form of a number of segments equal to the spermatocyte 

 number of chromosomes. 



At this time begins a change which has rarely been observed in male 

 cells. The chromatin segments begin slowly to break down, and their 

 substance becomes aggregated about the accessory chromosome, thus ap- 

 parently increasing the size of this body enormously. The disintegration 

 of the chromatin threads is very gradual, as is shown by comparing Fig- 

 ures 1 1-14. In Figures 12, 13, the process is well begun, and the remain- 

 ing chromatin segments are very diffuse and flaky, although they still 

 stain like ordinary chromatin, the only difference apparently being that 

 the granules are farther apart. From this fact it is, I believe, impos- 

 sible to argue that the chromatin is actually dissolved and the solution 

 deposited in or about the accessory chromosome. On the contrary, the 

 mass of granules is merely rearranged and aggregated without change in 

 chemical state about this element. It is merely a mechanical rearrange- 

 ment of the chromomeres, not a chemical change, which takes place. Some 

 idea of the time required to accomplish the complete rearrangement of 

 the elements of the nucleus may be gathered by comparing the size of 

 the cells in the different stages of disintegration (Figs. 11-15). 



As the rearrangement of the chi'omatin proceeds, the framework of the 



