RESULTS OF CEOSSING TWO HBMIPTEROUS SPECIES. 479 



the genital spot. For convenience we repeat the argument £rorn our 

 preliminary report. ' 



Both Morgan and Doncaster class the genital spot o£ variolarms with 

 the secondary sexual characters of authors, and they therefore interpret our 

 results as not having the bearing on the theories o£ sex-determination which 

 we claim for them. Now our claim has been that the genital spot of vario- 

 larius is an integral part of the male genital segment — the structure of the 

 female genital segment being such that the spot could not be present in this 

 segment without changing the form of the segment itself — and we have 

 claimed that therefore a study of the transmission of the genital spot should 

 give a trustworthy indication of the method of transmission of the entire 

 genital segment. 



This claim, that the method of transmission of the genital spot should be 

 an index of the method of transmission of the genital organs of the male, 

 has been completely justified by further work on these hybrids. . . The 

 genetic results from our study of the genital spot of variolarms may be open 

 to the criticism that as the spot is " not directly connected with the act of 

 reproduction " it should be classed with the secondary sexual characters ; 

 but the intromittent organ is certainly free from such criticism and can be 

 justly classed as a primary sexual character. In view of the fact that our 

 results from the study of the transmission of the variolarms spot have been 

 set aside on the ground that the spot is a secondary sexual character, and 

 therefore has no bearing on the problem of the determination of sex, it is 

 necessary first to "establish the claim that the intromittent organ can be 

 -classed with the primary and not the secondary sexual characters. This 

 apparently ought not to be difficult, but a difficulty does arise owing to the 

 fact that recent authors who have discussed secondary sexual characters have 

 avoided defining them, and have neglected to state wherein they are to be 

 distinguished from the primary sexual characters. 



According to Darwin ('59) Hunter defines secondary sexual characters as 

 follows : — 



"The term, secondary sexual characters, used by Hanter, applies to 

 characters which are attached to one sex ; but are not directly connected 

 with the act of reproduction.^' 



Darwin ('86) adopts Hunter's classification of primary and secondary 

 sexual characters, but shows that even such an apparently clear-cut defini- 

 tion encounters difficulties. He says* : — " With animals which have their 

 sexes separated, the males necessarily differ from the females in their organs 

 of reproduction ; and these afford the primary sexual characters. But the 

 sexes often differ in what Hunter has called secondary sexual characters, 

 which are not directly connected xoith the act of reproduction ; for instance, in 



* The italics are ours. 



