478 MISSES K. FOOT AND E. C. STKOBELL : 



The results from the backcross demonstrate again tliat the genital spot and 

 the introinittent organ are not linked in inheritance (Table 11). Twelve o£ 

 these eighteen speciiiiens have the E. va7iolarius spot on the genital segment, 

 while only three have a length o£ intromittent organ characteristic of 

 varlolarius. Six have a spot on the genital segment which is more or less 

 reduced by the inheritance from E. servus, which has no genital spot. These 

 six are therefore intermediate as to the genital spot, while there are fifteen 

 intermediate in the leno-th of the intromittent organ. 



C/ii'omosomes. 



Our experiments with these hemiptera w^ere undertaken with the aim of 

 testing some recent chromosome-theories of sex-determination by the 

 trustworthy method of exj)erimental cross-breeding. For this purpose we 

 selected an exclusively male character — the distinct dark spot which is present 

 on the genital segment of Eu.9chistus variolarius and absent in Eucldstus 

 sermis, for this character appeared to us well adapted to test the function of 

 the so-called sex-chromosomes in the transmission of an exclusively male 

 <;haracter. 



The results of these cross-breeding experiments and their bearing on the 

 chromosome-theories of sex-determination have been discussed in earlier 

 papers, Foot and Strobell, '13 and ^14 a & h. In the present paper we 

 will sumuiarize the evidence in order to demonstrate that the results gained 

 by the study of the transmission of the genital spot are in fact duplicated 

 in the case o£ the intromittent organ, and that therefore not only is the 

 evidence gained through the study of the first greatly strengthened, but 

 the conclusions bearing on chromosome-theories are fully sustained on 

 every point. 



In the preliminary report o£ our results from the study of this second 

 exclusively male character we gave what appear to us very cogent i-easons 

 for claiming that this character should be classed as a primary sexual 

 character. Both Morgan ('13) and Doncaster ('14rtr, & 'll/'O? iii the case of the 

 genital spot summarily dispose of our results and our claim that they have 

 a valid beai'ing on the chromosome sex-determination hypothesis, by simply 

 classing the genital spot with secondary sexual characters. Although there 

 might be some ground for classing the genital spot with these characters, 

 they ai'e quite unlike in a most important feature, for a marked characteristic 

 •of the secondary sexual characters of authors is the fact that they can, 

 almost without exception, be bred into the opposite sex. We do not believe 

 that even these critics can thus dismiss the evidence obtained from a 

 study of the transmission of the intromittent organ, although this evidence 

 confirms in everv detail the results demonstrated in the transmission of 



