BLACKMAN. — SPERMATOGENESIS OF THE MYRIAPODS. 493 



the result of the union in pairs of the spermatogonia! chromosomes 

 during the telophase of the last mitosis of the division period. 



Evidences of the nature of this union are to be seen in many nuclei, 

 although, owing to the close grouping of the chromosomes in the telo- 

 phase, actual stages in the union are very difficult to find. In the two 

 species of Scolopendra (Blackman, :03, :05, :05'') it has been shown 

 that this union of the chromosomes is accomplished by an end to end 

 fusion of the elements, similar to that described by Montgomery (:00, 

 :0l) for Peripatus, and by Sutton (:02) for Brachystola. In the three 

 species of Lithobius studied, evidences of the origin of the spermatocyte 

 chromosomes by a similar union are seen in Figures 3 and 4. The 

 chromatin segments are often bent at a sharp angle at about their 

 middle point, the two equal limbs representing spermatogonia! chromo- 

 somes which have conjugated during the preceding telophase. Thus 

 in Lithobius, just as in Scolopendra and in Scutigera, there is no stage 

 in which all of the chromatin is arranged in a continuous spireme, and 

 at no time is the number of chromatin segments less than the number 

 of chromosomes characteristic of the succeeding metaphase. 



In the meantime, even before the reconstruction of the daughter 

 nuclei in the last spermatogonia! telophase, the cells have entered 

 upon that period of remarkable growth characteristic of the spermato- 

 cytes of chilopods. This growth is so marked that at the time of the 

 appearance of the nuclear membrane (Figures 3, 4) each of the daughter 

 cells has attained a size about equal to that of the parent cell. In 

 succeeding stages this increase in size continues (Figures 3-8), until 

 finally in the vesicle stage (Figure 10) the diameter of the spermato- 

 cytes is more than ten times that of cells in the spermatogonia! telo- 

 phase. Thus the ultimate size of the spermatocyte in the vesicle stage 

 is even greater than in Scolopendra. 



At the time of the reconstruction of the nuclear membrane, as has 

 already been mentioned, chromatin segments of the reduced number 

 become scattered throughout the entire nuclear cavity (Figure 3). As 

 the cell continues to grow these chromatin threads become more diffuse 

 and the granules composing them become finer, and are now in a con- 

 dition apparently similar in all respects to the segmented spireme stage 

 of the spermatocytes of other animals. Now, however, a rearrange- 

 ment of the chromatin begins to take place, which seems to be charac- 

 teristic of chilopod spermatocytes and is seldom met with in the male 

 cells of other animals. These changes have been studied in detail in 

 Scolopendra (Blackman, :03, :05, :05^) and in Scutigera (Medes, :05), 

 and while they are essentially similar in these two genera, they still 

 present several interesting minor differences. 



