332 KATHARINE FOOT AND E. C. STROBELL. 



"If we measure the amount of the variolarius inheritance in 

 this back-cross, we find an astonishing agreement between the 

 theoretical expectation and the actual result. The relative 

 amount of variolarius to servus in the offspring of this back- 

 cross is 3 to i , and we should expect, therefore, the mean length 

 of the intromittent organ of servus to be reduced by 75 per cent, 

 of the difference between the mean lengths in variolarius and 

 servus. This difference is 69.71 mm., 75 per cent, of this being 

 52.28 mm. Deducting this from the mean length of the organ 

 of servus (166.41 mm.) would leave 114.13 mm. as the mean 

 length of the organ of the offspring from this back-cross. The 

 mean length is in fact 113.47 mm., this being only 0.66 mm. less 

 than the calculated expectation." 1 



If our results had followed a Mendelian type of inheritance, 

 assuming the servus length of organ to be dominant, we 

 should expect the mean length of the intromittent organ to be 

 approximately 131.33 mm. instead of being the above simple 

 expression of the proportion of inheritance from the two species. 



This result would seem scarcely to merit serious consideration, 

 as it was based on the inheritance from only 18 males; but from 

 the back-cross reported in the present paper (variolarius- 

 ictericus} we succeeded in getting 76 males and these repeat the 

 evidence given by the 18 males of the first experiment. 2 



The two experiments are entirely similar except that in the 

 first experiment the back-cross was made with a male of the 

 same species as the female of the first cross (variolarius} and in 

 the second experiment the back-cross was made with a male of 

 the same species as the male of the first cross (ictericus}. 



If we look for an agreement in results from the two experi- 

 ments, we should expect the mean length of the intromittent 

 organ of the 71 males from the second back-cross to show a like 

 quantitative response in inheritance to that in the case of the 

 1 8 males of the first experiment. 



In this second back-cross we have 3 parts ictericus to I vario- 

 larius, and we should expect the mean length of the intromittent 



iFoot and Strobell, '15, "Results of Crossing Two Hemipterous Species with 

 Reference to the Inheritance of two Exclusively Male Characters," Journ. Linn. 

 Soc. London, Zool., Vol. XXXII.. p. 474. IP^S- 



2 The intromittent organs of 71 of these 76 males were measured. See page 329. 



