484 Alice M. Boring 



behind the others in going toward the spindle pole (Figs. 25 

 and 27). The chromosomes mass together in the anaphase, so 

 that as soon as the odd chromosome joins the others, it is no longer 

 possible to distinguish it (Fig. 28). 



The spindle fibers stand out very clearly, especially in the mate- 

 rial fixed in Flemming or Hermann, and it is noticeable that the 

 odd univalent chromosome is joined to only one pole by its mantle 

 fibers, while the bivalent chromosomes are attached to both. 



During the telophase the granules of a "Zwischenkorper" can 

 be seen on some (Fig. 25) or all (Fig. 26) the spindle fibers. These 

 show only in iron haematoxylin preparations which have not been 

 extracted very thoroughly. In such preparations the centrosomes 

 of the first spermatocyte division can also be seen (Fig. 23). They 

 divide during the anaphase of the first division (Figs. 25 and 27) 

 in readiness for the second division which succeeds the first without 

 any reconstruction of the nucleus. 



The chromosomes rearrange themselves (Fig. 29) into a plane 

 at right angles to the plane of the first division, and soon form a 

 regular equatorial plate. Half of the second spermatocytes con- 

 tain 10 chromosomes (Fig. 31) and the other half 11 (Fig. 30), that 

 is, 10 plus the odd chromosome. In the cells containing 11 chro- 

 mosomes, the odd one does not difi^er enough in size to make it 

 any longer distinguishable. In this division, all the chromosomes 

 in all of the cells divide. The reasons for this conclusion are: (i) 

 the lateral views of the metaphase (Fig. 32) never show one undi- 

 vided chromosome among the other dividing ones, (2) all the chro- 

 mosomes are attached by mantle fibers to both spindle poles, and 

 (3) in the anaphase, there is never a lagging chromosome near one 

 pole without a mate at the other pole (Fig. 33). That this division 

 of chromosomes is at right angles to the first, that is, longitudinal 

 and equational, is certainly conditioned by the formation of the 

 spindle w^hich is derived directly from that of the first division. 

 The same fibers between the chromosomes and centrosomes 

 remain intact, and as the centrosome divides, the chromosomes are 

 pulled into an equatorial plate at right angles to the equatorial 

 plate of the first spermatocyte division. This second division 

 therefore corresponds to the preliminary longitudinal splitting of 



