REPTILIAN SPERMATOGENESIS 289 



that has been seen in the earher spireme stages, and so it has 

 been marked X in all cases. 



In this place it should be emphasized that this early migration 

 of the X-chromosome is not seen in all side views of the spindles. 

 One may examine several dozen cells without finding the X-ele- 

 ment lying far out of the division plane, although, after a little 

 experience, it can usually be recognized. But again one may 

 find a patch of dividing cells in which the X-element will show 

 up conspicuously, as in figures 9 to 14. This probably 

 means either that the X-element goes to one pole a little in 

 advance of the other chromosomes or that typically it moves 

 at the same time the other elements divide, but occasionally 

 may go early to one pole. In either case the infrequency of the 

 phenomenon would be explained. 



Aside from the fact that the X-element does not divide, the 

 first maturation division proceeds normally. Late anaphases 

 show five macro-chromosomes at one pole and six at the other 

 (figs. 15 to 17), the extra chromosome being the bipartite X- 

 chromosome.^ Thus the study of anaphase stages bears out 

 the observations that the bipartite element passes to one pole 

 of the cell undivided. Hence half of the second spermatocytes 

 will carry, and half will lack the X-element. 



Second maturation division. Following the first spermotocyte 

 division, the chromosomes of the young second spermatocyte 

 enter into a spireme condition. No conspicuous nucleoli have 

 been observed in such resting nuclei. When the chromosomes 

 of the second division condense out of this resting nucleus, 

 they are generally already split in the plane in which they are 

 destined to divide. This precocious splitting (fig, 18) makes it 

 somewhat difficult to make accurate counts in the equatorial 

 plate view, because one does not know whether a given chromatin 

 mass is one chromosome already split or two chromosomes 

 lying side by side. Figures 19 to 21 show three cells in which 

 there are five macro-chromosomes. Figures 19 and 20 are 



^ In figures 17 and 21 the cell was viewed from one pole, so that in order to 

 show all the chromosomes, one pole was drawn, and then the cell shifted with 

 the mechanical stage until the other pole was clear of the first. 



