RESULTS OF CROSSING TWO HEMIPTEEOUS SPECIES, 457 



Results of Crossing two Heiuipterous Species, with reference to the 

 Inheritance of two Exclusively Male Characters. By Kathaeine 

 Foot and E. C. Steobell. (Communicated by Prof. E. B. Poulton,. 

 F.R.S., Pres.L.S.) 



(Plates 41-47.) 

 [Read 3rd June, 1915.] 



The results given in this paper are due to the interesting discovery made by 

 Dr. Eltringham of Oxford, that there is a marked difference in the length of 

 the intromittent organ of the two hemipterous species Euscliistus variolarius 

 and Kuscliistus servus. 



We feel greatl}^ indebted to Professor Poulton for kindly suggesting 

 Dr. Eltringham to us, in response to our expressed wish to find an 

 experienced entomologist in England who would be willing to study 

 E. variolarius and E. servus with a view of discovering some marked character 

 distinctive of each species that could be profitably studied in the hybrids. 



The result of Dr. Eltringham's investigations is of special satisfaction to 

 us, because the discovery of a difference in the length of the intromittent 

 organ of the two species offers a valuable control for the results obtained 

 and the conclusions we were able to draw from our study of the transmission 

 of the genital spot *, enabling us to compare the inheritance of these two 

 exclusively male characters in the same insect. 



During our experimental work on the genital spot (Foot and Strobell, 

 '13 & '14) we carefully isolated and preserved each insect, in the hope 

 that future investigation by an experienced entomologist might reveal some 

 other marked character in these insects that would enable us to determine 

 what relation, if any, might exist between the inheritance of a second definite 

 character and the inheritance of the genital spot in each hybrid. 



Having our material preserved in this way has made it possible for us to 

 demonstrate both the exact appearance of the genital spot and the exact 

 length of the intromittent organ in one and the same individual of the Fi and 

 Fg hybrids, and also of the offspring from the backcross. We have made 

 this comparison very simple by placing the photographs of the intromittent 

 organs demonstrated in this paper in exactly the same order in which the 

 photographs of the insects themselves were placed in our paper on the 



* This is a distinct blade spot which is present on the genital segment of the males of 

 Huschistus variolarius, and is a distinguishing feature of this species, while it is absent in 

 JE. servus. It is the presence of this exclusively male character which led us to cross 

 these two species, with the hope of putting to an experimental test the chromosome-theory 

 of sex-determination (Foot and Strobell, '13 & '14). 



LINN. JOURN. — ZOOLOGY, VOL. XXXII. 37 



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