5 8 McCLUNG. 



also by the fact that from this point to the following metaphase 

 the cavity of its vesicle remains distinct from that formed by all 

 the others. In these stages the vesicle of the accessory chromo- 

 some may lie on any portion of the nuclear membrane proper ; 

 in some cases occupying a position between the ' fingers ' or 

 sacculations of it (Fig. 34). This vesicular stage is of compara- 

 tively long duration, and is followed by a receding of the chro- 

 momeres from the membrane to form a chromatic rod, first loose, 

 rough, and granular, but gradually growing more slender, and 

 compact, and often becoming twisted (Fig. 16). It also betrays 

 a longitudinal split at a stage later than that at which a similar 

 occurrence is observable in the ordinary chromosomes, 



51. "From the middle prophases to the telophases, its con- 

 duct is so similar to that of the other chromosomes that it would 

 hardly be an error to speak of the cells of these stages as having 

 two nuclei, one having a single chromosome and the other a 

 large number, the small nucleus always lagging slightly behind 

 the large one. This lagging of the accessory chromosome is 

 nicely shown in Fig. 21, already alluded to, where in a stage 

 just before the metaphase the nuclear membrane is seen to be dis- 

 solved while that of the body in question is still intact. 



52. "In the last or transformation division of the secondary 

 spermatogonia, some differences are noticeable in the behavior of 

 the element under consideration. The vesicular stage seems to 

 be of slightly longer duration, and while, after its close, the same 

 condensation of the chromatin takes place, no longitudinal split 

 appears until the late prophases or ' ring stage ' of the sperma- 

 tocyte ; and in the course of the earlier prophases of the growth 

 period its vesicle gradually becomes fused with the nuclear mem- 

 brane, its outer half completing the smooth contour of the latter, 

 while its inner portion projects into the nuclear cavity. In this 

 stage it has the appearance of an irregular vesicle filled with a 

 homogeneous, darkly staining liquid or semi-liquid body, sus- 

 pended within the membrane of the nucleus. Later it again 

 becomes granular, and in the first spermatocyte division divides 

 as it did in the spermatogonia. 



53. " The resting stage of this element, as shown by its staining 

 violet with F lemming's three-color stain, is what I have called 



