506 



It may be noted in Figs. 3 and 4 that in these stages the centro- 

 some is present, lying in the sphere substance, and that, in fact, it 

 has divided and the two halves are ready to migrate and mark the 

 poles of the spindle. 



In the early prophase preparatory to the division of the primary 

 spermatocyte, as regards the early conditions of the chromosomes, 

 there seemed to be few regular features. One large ring, and one 

 filament taking on something the form of the frame of a tennis racquet 

 appeared with a fair degree of constancy, but the remaining chromatin 

 structures seemed to be grouped into indescribable masses in which 

 nothing definite could be determined relative to conjugation of chromo- 

 somes. Although nine is the number of chromosomes that ultimately 

 appear at the equator of the spindle for division, in the early pro- 

 phases there were at times more than nine separate chromatic areas. 

 Moreover, certain of these individual areas seemed occasionally to be 

 made up of a cluster of denser separate chromatin masses of such an 

 appearance as to incline one to suppose that possibly the univalent 

 components of the ordinary bivalent chromosome may in themselves 

 be compound in nature. This suspicion is farther strengthened by 

 the fact that instead of the two or three typically large round chromo- 

 somes of the equatorial plate stage, in both primary and secondary 

 spermatocytes some cases were observed in which these larger chromo- 

 somes were lobed or bore some two or three bud-like outgrowths and 

 were themselves appreciably reduced in bulk. Although careful search 

 was made, too few cases of these irregular forms were found to con- 

 stitute conclusive evidence of any kind. 



Whatever may be the nature of the changes in the early pro- 

 phase, the fact remains that nine chromosomes ultimately make their 

 appearance in late prophase and at the equator of the spindle of the 

 primary spermatocyte. Fig. 5 is a late prophase drawn from a smear 

 preparation which showed the individual chromosomes with great 

 distinctness. The elongated and curved odd chromosome is evident 

 at first glance. The remaining eight grade down with more or less 

 regularity from one large one to a noticeably small one; or one 

 might say there are three or four large ones, three comparatively 

 small ones and one (or two) of intermediate size (compare Figs. 5, 6, 

 7 and 8). 



When finally ready for division the chromosomes are grouped into 

 a band around the equator of a very heavy-fibred spindle from a side 

 view of which the odd chromosome may sometimes be seen side by 

 side with the other chromosomes, usually recognizable by its long 



