302 T. H. MORGAN 



one nascent nucleus to the other. Practically the same rela- 

 tions are shown in figure 22, where however, the two X's appear 

 to be passing into the larger cell. In figure 23 the two X's stand 

 end to end as is also the case in figures 24 and 25. It is not pos- 

 sible to determine into which cell they might have passed— pre- 

 sumably, however, one to each cell. In figure 26 this result 

 seems to have been attained, since each cell contained four auto- 

 somes, and one X. In figures 27, 28, 29 and 30, the division 

 having been accomplished, only the larger cell is shown. In 

 each case there are two X chromosomes and four autosomes in 

 the cell. 



There are some questions here of theoretical interest. The 

 autosomes appear to have acted as pairs, if one may judge by 

 the equal distribution to the daughter cells, which seems to have 

 taken place in many cases, although it can not be established for 

 all cases. As there are four autosomes of each kind their copu- 

 lation in pairs does not seem unexpected. The behavior of the 

 X chromosomes is unique. In some cases they have passed to 

 opposite poles and in this sense have acted as a pair, but in most 

 cases they have passed into the larger cell. The first spermato- 

 cyte division in phylloxerans and aphids is of such a kind, that 

 the X chromosome passes into a particular cell, i.e., it does not 

 pass indifferently to either pole. But as a matter of fact we do 

 not know whether the larger cell into which it passes is prede- 

 termined (by some polar relations in the cell) and the X chromo- 

 some follows this preexisting condition, or whether that cell be- 

 comes the larger one, which happens at the time of division to 

 contain more of the X chromosome (owing, let us say, to its ac- 

 cidental excentric position). If one may judge from the appear- 

 ance of the early stages of the first spermatocyte division, the 

 former alternative may seem more plausible. If this be the cor- 

 rect interpretation then the more usual case of the two X's going 

 to the same pole in the abnormal cyst would be due to their rela- 

 tion to a particular pole of the dividing cell. The exceptional 

 passage into the other cell would be due to one of them getting 

 caught by the constriction, so that it was necessarily detained 

 in the smaller cell. But the more nearly equal sizes of the 



