354 MISSES K. FOOT AND E. C. STEOBELL : RESULTS OF 



proved by the fact that it is transmitted through the female, and the female 

 does not have the Y chromosome, as this chromosome is an exclusively 

 mnle character. Photographs 7-57 show the males of the Fj and the Fg 

 generations. All these males are the hybrid descendants of one pure 

 vanolarius female, that was fertilized by servus—i\\e species that has no 

 genital spot ; and these hybrids show beyond question that the spot can be 

 transmitted through the female, some of the Fo males having as pronounced a 

 spot on the genital segment as that of the variolarivs males : e. g.. one or more 

 of the speciniens of photos 15, 23, 2&, 28, 32, 34, 35, 36, 40, 41, 46, 48, 55. 



Second. The results demonstrate that the genital spot can be inherited 

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

 is transmitted through the male, and the male-producing spermatozoon 

 does not have an X chromosome. Photos 62 to 06 show the males from an 

 Fi hybrid ? x a pure variolarius ^^ , and a comparison of these photo- 

 o-raphs with those of the F2 hybrid generation (photos 15 to 57) shows that 

 the oenital spot is inherited much more strongly from the pure variolarivs 

 male than through the Fj hybrid males ; this fact demonstrating that the 

 male variolarius, as well as the female variolarius, can directly transmit the 

 spot to the males. As, according to the hypothesis, these can be inherited 

 directly from the male, only through the male-producing spermatozoon, which 

 has no X chromosome : it follows tliat the spot can be inherited without the 

 aid of the X chromosome. This back cross further demonstrates, not only 

 the direct inheritance of the spot from the male, but also the inheritance of 

 the serms character, absence of spot. This was transmitted to the Fj 9 

 by the pure variolaiius ? of the first cross, and therefore ew Jiypothesi it 

 must have come from the female-producing spermatozoon of servus. This 

 back cross therefore demonstrates that an exclueively male character — the 

 genital spot — can be transmitted by the male-producing sp( rmatozoon, and 

 an exclusively male character — the absence of spot — can be transmitted by 

 the female-[)roducing spermatozoon, and that therefore these so-called sex- 

 determining spermatozoa do not differ functionally in their transmission of 

 an exclusively male character. In making thfse deductions, it is, of course, 

 necessary to accept, for the sake of the argument, the assumption of male- 

 and female-producing spermatozoa, an assum})tion which, we believe, is far 

 from being proved. 



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

 the production of the genital spot are located in any of the ordinary 

 chromosomes, they must be in at least both members of a pair of ordinary 

 chromosomes, for the spot 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 are carried by both members of a pair 

 of chromosomes, we must assume that the female carries an inhibitor for the 



