KESTJLTS OF CROSSING TWO HEMIPTEROUS INSECTS. 477 



is stronger than servus as regards the length of the intromittent organ, these 

 relations are reversed in the case of the genital spot, and this is further 

 demonstrated by those that are classed as intermediates, for of these more are 

 minus than pins intermediates. It is therefore clear beyond question that these 

 two exclusively male characters, the genital spot and the intromittent organ,, 

 are not linked in inheritance. These results are certainly out of harmony 

 not only with the chromosome-hypothesis of sex-determination, but with the 

 recent hypotheses of chromosome-distribution of unit factors. 



The evidence from the Fi generation is of less value, as we have only 

 11 specimens showing the inheritance of the genital spot, and we were not 

 able to measure the length of intromittent organ of all the eleven, as one was 

 destroyed in dissection. 



The results from the F^ generation are as follows : — 2 of the eleven^ 

 Fi hybrids are like servus in having no genital spot, and the remaining 9 are- 

 variable intermediates. The two that have the servus inheritance (without a 

 genital spot) have the following lengths of intromittent organ — 126 mm. and 

 121 mm. ; these lengths showing a stronger inheritance from variolarius as 

 to the intromittent organ, while both insects show tin exclusively servus 

 inheritance in the absence of the genital spot. 



The Fi hybrid that has the longest intromittent organ — 134 mm. (photo 11) 

 — has the strongest genital spot of all the eleven Fi hybrids, this again 

 demonstrating a significant absence of linkage in these two exclusively male 

 characters. 



The mean length of the intromittent organs of the 10 Fj hybrids is 

 124" 9 mm., this demonstrating a stronger inheritance from variolarius than 

 from servus. The difference between the mean length of variolarius 

 (96"70 mm.) and of servus (166"41 mm.) is 69*71 mm., and therefore an 

 exact intermediate between these two means would be 131'55 mm. — the 

 measure therefore of the stronger variolarius inheritance in these Fi hybrids 

 may be expressed by 7*46 mm. 



It is an interesting fact that the intromittent organ not only of this 

 Fj generation, but also of the Fg generation, shows a stronger inheritance 

 from variolaoius than from servus, the measure of the greater variolarius 

 influence being almost the same for the two generations, i. e., 7*46 mm. in 

 the case of the F| hybrids, and 7*13 mm. in the case of the Fg hybrids. 



While the intromittent organ of these 190 males shows a stronger inheri- 

 tance from the female original parent {variolarius) , the reverse is true of the 

 genital spot, for only 19 of these 190 males have a spot as strong as vario- 

 larius, while 74 are like the male original part (servus) in having no spot. 



It is not possible to make an accurate estimate of the influence of the 

 two species on the type of genital spot classed as intermediate, but there 

 are certainly more minus than plus intermediates, this further demonstrating 

 that the genital spot shows a stronger inheritance from servus than from 

 variolariics. 



