BLACKMAN : THE SPERMATOGENESIS OF SCOLOPENDRA. 27 



seen that the nuclear wall forming this depression is in process of 

 disintegration, and the linin of the nuclear space is becoming arranged 

 into fibres which point toward the centrosome and are apparently con- 

 tinuous with the short astral rays upon the side of the centrosome near- 

 est the nucleus (Plate 4, Figs. 48, 49). 



While these phenomena have been taking place in the cytoplasmic 

 structures of the cell, the nucleus has also undergone some very marked 

 changes. At about the time the centrosomes begin their divergent 

 courses upon the nuclear membrane the appearance of the karyosphere 

 is considerably modified. It no longer preserves the sharp outline 

 which, as a general thing, is characteristic of it during the vesicle stage ; 

 but even in thick, darkly stained sections its contour appears irregular 

 and its periphery seems granular. Upon studying thin sections tin's 

 change in appearance is explained. The dense mass of chromatin 

 threads forming the karyosphere is becoming more loosely arranged. 

 The spireme is no longer so closely packed as formerly, but in favorable 

 sections appears as shown in Figure 19, e, or as in its tangential section 

 seen in Figure 22. Figure 19, e is a section through the centre of 

 the karyosphere, and shows upon one side a dense body (doubtless the 

 accessory chromosome), while the remainder of the chromatin is in the 

 form of a loose spireme. In Figure 22 the karyosphere is cut through 

 one side, showing at certain places denser aggregations of the chromatin 

 granules. These aggregations undoubtedly represent cross sections of 

 chromatin threads. 



This loosening of the spireme becomes moi-e and more marked, until 

 the regular contour of the karyosphere is entirely lost and chromatin 

 threads project at several points upon its surface. These projecting ends 

 rapidly lengthen by the uuwinding of the chromatin filaments, and when 

 they have attained a certain length, become detached, forming slender 

 segments, which ai'e equal in number to the number of chromosomes 

 in the succeeding metaphase. As the number of these chromatin seg- 

 ments present in the nuclear vesicle increases, the size of the karyosphere 

 is proportionately decreased, so that it would seem to follow that the 

 chromosomes are derived from this peculiar bod}-. Even if it were not 

 possible to give more definite evidence from actual observations of all 

 the stages incident to such an origin of the chromosomes, this would 

 probably be a just assumption, although there would still be room for 

 doubt.. But as these stages exist and are very numerous in my material, 

 I think it is impossible for the observer to escape the conclusions I have 

 drawn from them. 



