72 H. B. GOODRICH 



unknown. Thus it may be that the time of disjunction is de- 

 termined by the mere mechanical mode of association or non- 

 association of the members of the complex. In one case the 

 X-elements must necessarily follow the distribution of that part 

 of the bivalent group to which they are attached and in the 

 other they may be independent and free to divide equationally. 

 The occurrence of these curious compound X-groups at once 

 presents the question as to their significance. As pointed out 

 by Wilson ('11), Morgan ('10) and Gulick ('11) the behavior 

 and nature of the X-chromosome aside from its relation to sex 

 determination, also offers an interpretation of sex-linked in- 

 heritance, if we may assume that determinants other than those 

 influencing sex are also located in the X-chromosome. That 

 the X-chromosome may often be a compound element is shown 

 by Wilson ('12) in Lygaeus and a similar formation is here de- 

 scribed for the long component of the X-group. Here, however, 

 and in the various Hempitera that have been discussed, it is 

 by no means clear that the compound X-group behaves as a 

 unit at any time other than during the reduction division. The 

 separation of the elements in the Hemiptera has been mentioned. 

 In Ascaris incurva it has been noted that during the prophases 

 the X-components are widely distributed in the nucleus and 

 there is no evidence to show that there is any uniform behavior 

 during the second maturation division. Also the maturation 

 divisions in the female do not support this contention; the micro- 

 some, the most readily identifiable unit of the female sometimes 

 lies in the peripheral ring of chromosomes in which are also 

 often found the large cross-formed autosomes, indicating that 

 the X-components are not at least centrally located in the plate 

 and that they may be quite irregularly distributed throughout 

 the plate. Thus there is* no visible evidence to support the 

 contention that the X-elements may behave in the female as 

 a unit anS not undergo along with the autosomes the random 

 assortment of synaptic pairs which Sutton ('03) pointed out as 

 a probable basis of Mendelian inheritance. Therefore, while 

 the fact that the compound group is distributed exactly as a 

 single X-chromosome during the differential division in the 



