RESULTS OF CROSSING TWO HEMIPTEROUS SPECIE^. 



variolarius contains one such chromosome and it follows when 

 the egg is fertilized by E. servus it will have one diploid pair of 

 chromosomes that is homologous for the factors producing a 

 male, but heterozygous for the factors producing the spot. 



Such a diploid pair should be present in all the offspring 

 both males and females, and if we cancel it in the females by 

 assuming an inhibitor somewhere, we still have it in the males 

 and therefore the spot should be quite as pronounced in the 

 FI hybrid males as in E. variolarius. The facts, however, are as 

 follows: None of the n male hybrids have a spot as strong as 

 E. variolarius, 2 have no spot whatever, 3 have a faint spot like 

 that of the third bug from the bottom of the tube in photo 4 

 4 have a slightly stronger spot, and 2 have a spot about one- 

 third as pronounced as that of E. variolarius. The genital spot 

 in the FI hybrids is very variable, it is not expressed as a domi- 

 nant, a recessive or a true blend. 



If we attempt to explain these results in terms of chromosomal 

 distribution of the factors, we encounter serious difficulties and 

 are forced to assume the illogical position of suggesting a method 

 of chromosome division for the hybrids which obviously does not 

 occur in E. variolarius, as the spot is not variable in this form. 



Assuming that the diploid pair of chromosomes in the egg of 



E. variolarius, which was fertilized by E. servus is heterozygous 

 for the spot factors (that they are in chromosome A, for example, 

 of the pair AB), then it must be asked why those in chromosome A 

 are completely suppressed in some of the FI hybrids, while part 

 of them find expression in other hybrids. 



We might simply assume that some of the factors of chromo- 

 some A have dropped out, but the facts show this to be untenable 

 for the spot reappears in the F 2 generation in some cases quite 

 as pronounced as in the pure E. variolarius. We must thus 

 assume that the female variolarius has at least half the spot 

 factors which she transmitted to the male hybrids, although these 



F, hybrids show either no spot at all or an incomplete spot. 

 To account for these facts we must assume that the male hybrids 

 differ from the pure males in having an inhibitor that inhibits 

 those spot factors which are present but which are not ex- 

 pressed. We have seen that the facts will not allow placing the 



