CROSSING TWO HEMIPTEROUS SPECIES. 2IQ 



We concluded that if one assumes (for the sake of the argu- 

 ment) that the spot factors are in a diploid pair of chromosomes, 

 it becomes necessary to assume other factors outside the chromo- 

 somes. We called such hypothetical factors "inhibiting factors" 

 and we said of them: "We are forced to admit that inhibiting 

 factors whatever they are must be located outside the chro- 

 mosomes, in the region of pure hypothesis." 



Morgan appears to accept this, calling such hypothetical 

 factors ''things in the cell" and symbolizing them as A. B. C. 

 He says "the result (or character) that a factor produces depends 

 on its relation to other things in the cell (here A. B. C.)," and he 

 adds, "We are dealing, then, not with the relation of X to S 

 alone, but this relation in turn depends on the proportion of both 

 X and S to A. B. C." 



In the above-quoted paragraph he includes in his explanation 

 the assumption of a relation between the spot factors and the X- 

 chromosome, and this we believe is a part of his explanation 

 which is not sustained by the facts. The spot can be transmitted 

 directly from the male to his male offspring and therefore this 

 must be by the male-producing spermatozoon (if there is such 

 a thing) and the so-called male-producing spermatozoon has no 

 X-chromosome. It is impossible to believe that in such cases the 

 inheritance of the spot is dependent upon the relation of the spot 

 factors of the sperm to the X-chromosome in the egg, especially 

 if the cross is made with a pure servus egg. Morgan evidently 

 thinks this is possible, however, for in his explanatory diagram 

 he illustrates a cross between E. servus 9 X E. variolarius cf , 

 a cross which we explained we were unable to attempt on account 

 of scarcity of material. 



His diagram, if assumed to be an explanation based on the 

 facts of our experiments, is further in error in its illustration of 

 the FI hybrids. In his simple Mendelian scheme all the FI 

 hybrids are illustrated as typical heterozygotes and the fact is 

 ignored that two out of the eleven of our FI hybrids are like servus 

 in having no spot. If such a modification of the spot can be 

 caused by "other things in the cell," it would seem that merely 

 calling these "A. B. C." is no explanation of the results. 



Morgan excuses his attempted explanation on the ground 



