No. 574] 



INHERITANCE 



5S1 



suffices to call forth in some degree the spot in the hybrid. 

 Its intensity varies from a condition approaching that in 

 pure variolarius to a faint spot (possibly even to no spot 

 at all). The F x results show also that a single factor in 

 the female fails to cause the spot to develop in that sex. 

 In the F x male the failure of the spot to reach in most 

 cases its full development shows obviously that the same 

 conditions that produce a male that is perfect so far as 

 his sex gonad is concerned, do not suffice to cause the full 

 development of the spot, although the factor for the spot 

 is present in one dose at least. The only confusion that 

 is liable to arise is that in none of the F 2 females did the 

 spot appear, although in some of them there must have 

 been a double dose of spot. But the difficulty is imaginary 

 as a little thought will show. In the first place the female 

 of E. variolarius herself does not show the spot, yet this 

 female must have a double dose of spot if spot is in the 

 X chromosome or in- any other chromosome (except the Y). 

 Foot and Strobell by an elaborate analysis of the case 

 show that the factor can not be carried by either the X or 

 the Y chromosome. It is unnecessary to repeat their 

 argument ; for, if the factor were carried by the X chromo- 

 some, only half of tlic grajidx.li> >lwmld show it, while, in 



not be carried by the Y chromosome because the Y chromo- 

 some of variolarius is not present in the female, hence 

 could not have entered the cross as made. We are con- 

 cerned then only with a third possibility, viz., that there is 



