232 KATHARINE FOOT AND E. C. STROBELL. 



the sex-chromosomes any closer than we have shown by experi- 

 ment is the case between these chromosomes and the genital 

 spot and intromittent organ. Those who would place these 

 factors in the chromosomes must concede that they must be in 

 at least a pair of autosomes; there seems indeed no reason for 

 assuming a different mode of transmission for the testes than for 

 the other exclusively male characters the genital spot and the 

 intromittent organ. We feel we are therefore justified in our 

 claim that the mode of transmission of the genital spot and 

 intromittent organ is an index of the mode of transmission of the 

 reproductive glands themselves, and that our cross-breeding 

 experiments offer direct evidence against the chromosome theory 

 of sex-determination. 



If we reconsider Morgan's suggestion that "the factors for 

 producing a male must be located in some other chromosome" 

 than the X-chromosome, and we interpret "some other chromo- 

 some" as a pair of autosomes (as Morgan does in his formula) this 

 would locate the factors for the testes in this pair of autosomes 

 and be quite in harmony with our conclusions, that factors for 

 exclusively male organs, if carried by chromosomes, cannot be 

 in less than a pair of chromosomes and it supports our claim 

 that the method of transmission of the genital spot and intro- 

 mittent organ is an index of the method of transmission of the 

 testes. 



Morgan's formula 



Gametes of female X M X M 

 Gametes of male X M M. 



gives the female zygotes (X M + X M) just as many factors for 

 "producing a male" (MM) as it gives for producing a female 

 (X X) but he does not tell us what determines that the X gametes 

 shall predominate. 



According to Morgan's formula the term "female-producing 

 spermatozoon" (X M) would appear to be a misnomer, for it 

 carries "the factors for producing a male" as well as the factors 

 for producing a female. The male-producing spermatozoon, 

 on the contrary, carries the factors for producing a male only (M). 

 The female-producing spermatozoon therefore can transmit 

 exclusively male characters, as we have shown is the case, but 



