EESULTS OF CROSSING TWO HEMIPTEROUS SPECIES. 471 



In the F2 generation the extremes o£ the genital spot {i. e., its full size and 

 its complete absence) are represented, 19 of the F3 hybrids having a genital 

 spot almost if not quite as pronounced as the pure variolarhts species, and 

 74 having no spot like ]^. sei^vus. 



"Seventh. Size-characters, in common loith all characters {even those that 

 Mendelize), show quantitative variation^ — Quantitative variation is of course 

 more accuratel}^ demonstrated in the case of the intromittent organ than in 

 the genital spot, though it is present in both these characters. Table 1 shows 

 that in 62 specimens of E. variolarius the length of the organ varied between 

 85^ mm, and 106 mm., the range of the variation between the shortest and 

 the longest being 20-5 mm. The table gives the number of specimens havino- 

 the various lengths, and it demonstrates that there is no definite ascending or 

 descending scale of variation in relation to the number of specimens havino- 

 a given length of the organ, though the extremes are represented by only 

 one specimen, and lengths near the mean are more frequently represented. 



This is true also for E. servus as demonstrated in Table 2. This table gives 

 the lengths of the intromittent organs for &2 specimens, and shows that this 

 length varies between 146 mm. and 182 mm., the range of the variation 

 between the shortest and the longest being therefore 36 mm. 



Variations in the length of the intromittent organ may be quite independent 

 of the relative size of the insects, not only in the hybrid generations, but also 

 in the pure species : for example, the photographs of the two intromittent 

 organs shown in photo 6 measure 104 mm. and 94 mm. The two insects 

 from which these organs were taken are brothers of the E. variolarius female 

 of the original cross. The one having the longer intromittent organ (101 mm.) 

 is decidedly the smaller insect, the actual width of the pronotum (between 

 the humeri) being 8^ mm., while the pronotum of the insect with the shorter 

 organ measured ^^ mm. 



Quantitative variation in the genital spot, though more diflScult to 

 demonstrate than in the intromittent organ, can be appreciated by comparino- 

 the male offspring from the same parents. 



It is clear that all the points taken up tmder the above seven headings 

 apply to the genital spot with quite as much force as to the intromittent 

 organ — the size of the genital spot, like the length of intromittent oro-an 

 showing a type of inheritance that is nearly in full accord with Castle's 

 observations on size-characters. In earlier papers these facts were clearlv 

 stated in the case of the genital spot (Foot and Strobell, '13 & '14 a), but it 

 is interesting to note that Morgan ('14) interprets such evidence quite 

 differently from Castle, for he says, " the authors'" evidence shows that it 

 (the genital spot) is inherited as are Mendelian characters'"' (pao-e 481). 



We do not feel justified, in view of the narrow limits of our experiments 

 in genetics, in attempting to draw conclusions as to the possible beai'ino- of 



