194 KATHARINE FOOT AND E. C. STROBELL. 



chance discarded the other A in her polar body, she also would 

 have the spot, and further, half the male producing spermatozoa 

 have the A chromosome and therefore they must not function or 

 the spot would be absent in half the variolarius males. 



If we place the inhibitor in the three X chromosomes, the 

 assumption obviously would not work, for the male has one of 

 the three X chromosomes and the spot would therefore be 

 inhibited in the male as well as in the female. It would therefore 

 be necessary to assume that in E. variolarius two doses of in- 

 hibitor are necessary to cancel the spot. This assumption, 

 which apparently would hold for E. variolarius, is, however, 

 found to be untenable if used to explain the results of the cross 

 between E. variolarius and E. servus, for the female hybrid can- 

 not receive a double dose unless we assume that E. servus carries 

 an inhibitor for inhibiting in the female a male character which 

 is never present in the male. If, however, we feel justified in 

 assuming that the female hybrid has a double dose of inhibitor, 

 this would fail to explain the absence of the spot in those male 

 hybrids, which do not have it, for they have only one X chromo- 

 some and therefore only one dose of inhibitor. We might avoid 

 this by assuming that one dose only would be necessary for the 

 female hybrid, as she presumably has only one dose of spot 

 factors; but this would involve inhibiting the spot in all the FI 

 males also, which is opposed to the facts, as the spot is not in- 

 hibited in all the Fj hybrids. The facts show that the spot 

 factors whatever they are are latent in the female and if they 

 are suppressed by an inhibiting factor, it would seem that this 

 cannot logically be located in a definite chromosome. 



Our results demonstrate that the spot is by no means a unit 

 character. If we speak of it in terms of Mendelism we must 

 say that it is the result of a large number of unit factors, for in the 

 107 males of the F 2 generation in which a spot can be identified, 

 it is present in every degree of intensity, from a mere indication 

 of a spot to those which are nearly, if not quite, as conspicuous 

 as the spot of a pure variolarius (Photos 2-4). 



If we assume that each member of one diploid pair of chromo- 

 somes contains all or half the factors for the genital spot, in 

 addition to the factors for maleness, then the ripe egg of E. 



