EESULTS OF CROSSING TWO HEMIPTEROUS SPECIES. 469' 



expect to find these two exclusively male characters in the Fg hybrids in 

 the following ratio :^25 % like variolarius, 25 7o like servus, and 50 7o 

 intermediates. We ought to find 47 o£ the 190 Fg hybrids like variolarius, 

 47 like servus, and 94 intermediates ; whereas we find in the case of the 

 intromittent organ 14 like variolarius, 7 like servus, and 169 intermediates 

 (see Table 10), and in the case of the genital spot 19 like variolarius, 74 like 

 servus, and 97 intermediates (Table 10). Both characters — the intromittent 

 organ and the genital spot — are therefore like other size- characters in 

 their failure to show Mendelian segregation in the Fg generation. 



'^Fourth. — There is increased variability in the F^ generation as compared 

 with the Fi generation." — This appears at first sight to be true both for the 

 intromittent organ and for the genital spot, but the evidence is unsatisfactorv 

 in that the number of individuals is so very different for the two generations, 

 and, as variation is present in both generations, we must expect the larger 

 number to give the larger number of variations. We have the exact length 

 of the intromittent organ for 190 specimens of the F2 generation, but have 

 it for only 10 of the Fi generation. There are 69 variations of length in the 

 190 F2 hybrids (Tables 3 to 9), and only six variations in the ten Fi hybrids. 

 The latter, however, represents more variations in relation to the number of 

 specimens than the 69 variations in the 190 F2 hybrids. 



These relations hold true also in the case of the genital spot, though 

 the evidence here is not so exact, as the differences cannot be accurately 

 measured as in the case of the intromittent organ. 



On the whole we are not justified in claiming that the evidence is in 

 accord with the observations on those size-characters which show that 

 " there is increased variability in the F2 generation as compared to the 

 Fi generation ". 



" Fifth. The F^ generatioji, like the F-^, is intermediate in size." — This 

 point can again be most satisfactorily demonstrated in the c;ise of the intro- 

 mittent organ, for we know the mean length of the organ for both parent 

 species, for the Fj generation, the F2 generation, and for the seven separate 

 families of these F2 hybrids. 



As stated above, the theoretically precise intermediate between thejmean 

 lengths of the two parent species would be 131*55 mm. 



The following are the mean lengths of intromittent organ of the F2 males, 

 from the seven pairs of Fi hybrids : — 



1st pair of Fj hybi'ids 123*14 mm. (table^S). 



2nd pair of Fi hybrids ...... 120-67 mm. (table^l). 



3rd pair of Fi hybrids 126-92 mm. (table 5). 



4th pair of Fi hybrids 128-27 mm. (table 6). 



5th pair of Fi hybrids 124-37 mm. (table 7). 



6th pair of Fi hybrids 126*33 mm. (table 8). 



7th pair of Fi hybrids 122-29 mm. (table 9} . 



