RESULTS OF CROSSING. 331 



stronger than any of the genital spots of the pure ictericus males. 



The variolarius-servus crosses further demonstrated that the 

 genital spot was transmitted directly from the male and this is 

 also supported by the variolarius-ictericus back-cross. The 

 ictericus inheritance is shown in all the photographed specimens 

 in which the spot is quite as insignificant as the faintest spot in 

 the pure ictericus specimens. 



Although the harmony in results with those of the servus 

 experiments is evident, the factor of an indefinite spot in ictericus 

 makes a detailed comparison less satisfactory and for this reason 

 we shall discuss the results from the two back-crosses in relation 

 to the intromittent organ rather than the genital spot. These 

 two exclusively male characters (as we demonstrated by the 

 servus crosses) give exactly the same evidence, in every detail, 

 in their bearing on current theories under discussion. 



RESULTS AND DISCUSSION. 



The results obtained from this back-cross, Fj. 9 (from vario- 

 larius X ictericus} by ictericus, are so nearly a repetition of those 

 obtained from the back-cross of FI 9 (from variolarius X servus) 

 by variolarius, that they would seem scarcely to merit separate 

 publication: but for the fact that the results obtained from the 

 few specimens secured from the latter cross were of small sci- 

 entific value, until supported by more data, and such data 

 (from ictericus} were not in shape for publication when the 

 results of the servus cross went to press. 



One point of interest in the back-cross of FI 9 by variolarius 

 was that the offspring did not show a Mendelian type of in- 

 heritance, but that the length of the intromittent organ appeared 

 to be a quantitative response to the proportion of inheritance 

 from the two species. 



In attempting to measure the strength of the inheritance in 

 this cross, we found that the effect on the length of the organ 

 corresponded almost exactly with the relative amount of vario- 

 larius to servus in the offspring. This was 3 variolarius to I 

 servus, as variolarius was first crossed with servus and a male 

 variolarius used for the back-cross with the FI female. In our 

 report of this cross we stated the results as follows: 



