22O KATHARINE FOOT AND E. C. STROBELL. 



that we have failed to explain our results. We make no apology 

 for this. We believe the duty of the scientist is to curb the 

 natural temptation to force an explanation of individual results, 

 for science to-day is overburdened by premature and undigested 

 generalizations. We would aim rather to follow the example of 

 those scientists who are willing patiently and conscientiously to 

 collect data sustained by the hope that some day the facts may 

 be of value. 



Both Morgan and Doncaster class the genital spot of vario- 

 larius with the secondary sexual characters of authors and they 

 therefore interpret our results as not having the bearing on the 

 theories of sex-determination which we claim for them. Now 

 our claim has been that the genital spot of variolarius 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 trans- 

 mission 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. 



In the present paper we shall report the results from the 

 study of the transmission of a second exclusively male character, 

 and it seems to us that these results cannot be set aside as 

 having no bearing on "Sex and Heredity," for this second 

 exclusively male character is the male genital organ itself the 

 intromittent organ. The genetic results from our study of the 

 genital spot of variolarius 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 variolarius 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 



