334 KATHARINE FOOT AND E. C. STROBELL. 



cross though the evidence of the direct influence of the male parent 

 might be questioned in this cross, as we did not succeed in securing 

 any FI or F2 males, and this would leave open the question whether 

 the ictericus inheritance in these offspring was due in part to 

 direct inheritance from the male of the back-cross or wholly due 

 to indirect inheritance through the FI female. In the servus 

 experiments, on the contrary, the direct influence of the male 

 in both the first cross and the back-cross is beyond question. 



Evidence of the transmission of this exclusively male character 

 through the female is given in both back-crosses, but in the 

 variolarius by servus experiments it is most conclusively shown 

 by the mean length of the intromittent organ of the FI generation, 

 where the inheritance from the pure variolarius female of the first 

 cross is clearly in evidence. 



In the ictericus experiment, the inheritance from the pure 

 variolarius female of the first cross is shown in the increased 

 mean length of the intromittent organ of the offspring of the 

 back-cross as compared to that of the pure ictericus species. 

 The facts are as follows: 



Mean length of the organ 



In the variolarius species 96.70 mm. 



In the iclericus species 60.64 mm. 



In the offspring from the back-cross ... - 68.97 mm. 



A further point for consideration in the two back-crosses is 

 the fact that in the first (variolarius-servus) the 25 per cent, 

 inheritance is from the male of the first cross (servus) and in the 

 second (variolarius-ictericus) the 25 per cent, inheritance is from 

 the female of the first cross (variolarius). As in the one case, 

 this one quarter inheritance was received directly from the male 

 (servus) and in the other case indirectly through the female 

 (variolarius), and as these have so nearly the same value in the 

 offspring from both back-crosses, we would seem to have the 

 strongest evidence that the so-called male- and female-producing 

 spermatozoa do not differ quantitatively in their transmission 

 even of a character so exclusively male as the intromittent organ. 



In the variolarius-servus by variolarius back-cross we have 

 direct evidence that this exclusively male character the length 

 of the intromittent organ is transmitted by the so-called female- 



