280 THE UNIVERSITY SCIENCE BULLETIN. 



a deficient chromosome, Bridges' discovery has demonstrated, 

 in the first place, that deficiencies may occur in X-chromo- 

 somes ; in the second place, that the sex differentiators are lim- 

 ited to a part of the X-chromosome, for they did not occur in 

 that portion as least of the chromosome which has to do with 

 the above genes and which lies between the loci of the genes 

 for "rudimentary wing" and "fused." Now if such be the case 

 in Drosophila, then in Tettigidea we are justified in concluding 

 that the sex determinants may likewise be limited to a portion 

 of the chromosome, and since the animal which has here been 

 described as possessing one normal and one short X is a male 

 instead of a female, it seems safe to conclude that possibly the 

 missing portion of this chromosome contains the determiners 

 for sex, and further that in the genus Tettigidea at least these 

 determiners lie near one end, probably the distal end, of the 

 chromosome. 



TIME OF APPEARANCE OF THE LONGITUDINAL SPLIT IN 

 SOMATIC CHROMOSOMES 



This discussion can not be closed without reference to the 

 evidence afforded in figures 2 to 5 upon the question of the time 

 at which division of the chromosomes in somatic mitoses takes 

 place. In figures 2 and 3, late prophases of cells from the 

 follicular wall, any portion of a chromosome which happens to 

 run at all vertically shows distinctly in cross-section a second- 

 ary split at right angles to the very wide and apparent pri- 

 mary split. In figure 3, at the arrow point, such a portion of 

 chromosome No. 4 is drawn. Most of the chromosomes here 

 show the same. These cells have not yet entered upon the 

 metaphase stage of division. Division, when it comes, will 

 take place in the plane of the very apparent primary split. The 

 secondary split here present can only be for the next again 

 metaphase. This is shown much more conclusively in ana- 

 phases (figs. 4 and 5) from the same tissues. Here it is cer- 

 tain that division along the primary plane has taken place. 

 The daughter chromosomes in traveling to the poles of the 

 spindle show clearly the secondary split (fig. 5). It must be 

 remembered that these chromosomes are entering upon the 

 telophase stage of division, and go from that to the "resting" 

 condition of the cell. Such a split is likely the forerunner of 



