The Chromosomes of Euschistus variolarius, Euschistus 
servus and the Hybrids of the Fi and F2 Generations. 
By 
Katharine Foot and E. C. Strobell. 
With 2 Text figures and Plate XXXVL 
The chromosomes of Euschistus variolarius and Euschistus servus 
are peculiarly fitted to test the relation, if any exists, between the so- 
called sex-determining chromosomes and the transmission of an exclu- 
sively male or female character. The X Y chromosomes («sex-deternii- 
ning chromosomes») of both variolarius and servus are morphological 
structures which are sharply defined. There has beeil no controversy 
as to their presence and behaviour in these tivo species of Hemiptera and 
they are therefore most favoiirable for experiment. In order to test the 
relation between these two so-called sex-determining chromosomes and 
the transmission of an exclusively male character, we selected the deeply 
pigmented spot on the male genital segment of variolarius as a character 
well adapted for such an experiment. This spot appears only in the 
males of this species and is therefore an exclusively male character (text 
fig. 1). 
It seems only logical to conclude that if a given chromosome carries 
the factors for the male genital segment, it carries also the factors for 
the pigmented area on this segment — especially as there is no other 
siniilar pigmented area on any other part of the insect. Further the pig- 
mented area is never transmitted to the female, it is as exclusively male 
as are the male genital organs themselves. This pigmented area of vario- 
larius — the genital spot — is absent in the males of E. servus, and a 
cross therefore between these two species should offer a trustworthy 
experiment of the value of the X Y chromosomes in the transmission of 
an exclusively male character. 
