RESULTS OF CROSSING. 333 



organ of variolarius to be reduced by 75 per cent, of the difference 

 between the mean lengths in ictericus and variolarius. This 

 difference is 36.06 mm., 75 per cent, of this being 27.04 mm. 

 Deducting this from the mean length of the organ of variolarius 

 (96.70 mm.) would leave 69.66 mm. as the mean length of the 

 organ from this back-cross. The mean length is in fact 68.97 

 mm., this being 0.69 mm. less than the calculated expectation. 

 In both back-crosses the slightly stronger inheritance is in favor 

 of the shorter type of intromittent organ and from the species 

 giving 75 per cent, of the inheritance. 



The 71 males from this back-cross further support the results 

 of the first experiment as follows: 



The back-cross (variolarius-servus by variolarius} showed that 

 the length of the intromittent organ was transmitted directly 

 from the male and also indirectly through the female, and that 

 therefore the so-called male- and female-producing spermatozoa 

 do not differ functionally in their transmission of a character so 

 exclusively male as the intromittent organ. 



Its direct transmission by the male was proved by the decrease 

 in the mean length of the organ of the offspring from the back- 

 cross as compared with that of the F 2 hybrids and it is further 

 shown by the FI generation of the variolarius-servus crosses. 

 The facts are as follows: 



Mean length of the organ 



In the variolarius species 96.70 mm. 



In the servus species 166.41 mm. 



In the Fi hybrids 124.9 mm. 



In the F2 hybrids 124.42 mm. 



In the offspring from the back-cross 113.47 mm. 



The increase in the mean length of the organ in the FI hybrids 

 as compared with that of the variolarius species proves the 

 direct transmission from the male parent, and the decrease in 

 the mean length of the organ in the offspring from the back- 

 cross as compared with that of the FI and F 2 generations shows 

 again the direct influence of the male parent, the servus male 

 of the first cross increasing the length towards that of the servus 

 species and the variolarius male of the back-cross reducing it 

 towards the variolarius species. 



These results are supported by the variolarius-ictericus back- 



