482 MISSES K. FOOT AND E. C. STROBELL : 



We have briefly summarized these results in a recent paper (Foot and 

 Strobell, '14 a), and this summary will serve equally well for the second 

 exclusively male character — the intromittent organ . This can be demonstrated 

 by quoting the summary and changing it only enough to include the intro- 

 mittent organ with the genital spot, as follows : — 



First. Both the genital spot and the type of intromittent organ charac- 

 teristic of each species can be inherited without the aid of the Y chromosome. 

 This is proved by the fact that both are transmitted through the female, and 

 the female does not possess the Y chromosome, as this chromosome is an 

 exclusively male character. 



Second. Both the genital spot and the type of intromittent organ can be 

 inherited without the aid of the X chromosome. This is proved by the fact 

 (demonstrated by the backcross) that they are transmitted through the 

 male and ex Jiypothesi the male-producing spermatozoon does not have an 

 X chromosome*. 



We add, " In making these deductions it is, of course, necessary to accept, 

 for the sake of the argument, the assumption of male- and female-producing 

 spermatozoa, an assumption which, we believe, is far from proved.^^ (See 

 backcross p. 473.) 



xldvd. The results show that if we assume that the factors necessary for 

 the production of the genital spot and the intromittent organ are located in 

 any of the ordinary chromosomes, they must be in at least both members of 

 a pair of ordinary chromosomes, for the sj/ot is directly transmitted through 

 both the male and the female. 



Fourth. The results show that, if we assume that the factors necessary 

 for the production of the genital spot and the intromittent organ are carried 

 by both members of a pair of chromosomes, we must assume that the female 

 carries an inhibitor for the spot as well as for the intromittent organ, for 

 neither is present in any of the females, though both are transmitted by the 

 female, and therefore the factors for both are present, though not expressed. 



Fifth. The results show that, although it is necessary to assume an 

 inhibitor only in the females of the pure species, in the hybrids it becomes 

 necessary to assume an inhibitor in the mcdes also. 



In his recent criticism of our work, Morgan ('14) overlooks the fact that 

 the Fi hybrid males have the spot more or less suppressed. In these males 

 it is partly or wholly absent, and yet (like the females) they can directly 



* Morgan ('14) seems to think that this point could have been made solely from the evi- 

 dence of the Fo ratio. He says : " It is unnecessary to repeat their argument ; for if the 

 factors were carried by the X chromosome only half the grandsons should show it, while, 

 iu fact, many more than half of them show it." We do not feel that this evidence would be 

 conclusive, for it could be attacked by the assumption of an unequal death-rate— a con- 

 venient assumption which has been used more than once to excuse contradictory evidence. 



