614 SIDNEY I. KORNHAUSER 
purpose to review here the many papers on hemipteran and 
homopteran chromosomes, so it will suffice to say that, in spite 
of the many combinations found, the presence of one x-chromo- 
some in the cells of the male and two x-chromosomes in the cells 
of the female is the essential difference. It is true that each 
x-chromosome may be represented by a group of separate chro- 
matic elements and that the x-chromosome may be accompanied 
in the cells of the male by a y-chromosome, but these are rather 
subordinate details. We also know that this sexual difference 
extends not only to the cells of the gonads, but to the somatic 
cells as well (Morrill, 710, Hoy, ’16). The writer has definitely 
demonstrated that this also holds true for Thelia. The growing 
gonapophyses of the fifth nymphal instar were slipped out of 
their chitinous coverings and mounted in acetic carmine. Many 
clear and handsome metaphase plates were studied and drawn 
with the aid of a camera lucida. The female somatic cells 
showed regularly twenty-two chromosomes including two large 
x-chromosomes, whereas the male cells exhibited twenty-one 
chromosomes, of which the largest one was the x-chromosome. 
Two of these cells are shown in figure 51, 6b and 7. Thus the 
sex of the soma and gonads of insects is determined in the zygote, 
and there is at no time an indifferent sex gland which may be 
molded into testis or ovary by the soma in which it develops. 
This idea of the indifferent gonad was put forth by Doncaster 
(14), who, after reviewing the work on the arthropods describ- 
ing the physiological differences between males and females, 
states that perhaps the physiological differences are the primary 
sexual differences and that the ‘primitive gonad’ develops into 
an ovary on one hand or into a testis on the other in consequence 
of this. The peculiar nymph described on pages 594 to 598 of 
this paper illustrates nicely that the chromosomes determine the 
character of both the soma and the germ plasm. ‘This individ- 
ual with the soma of a female had male gonads and a cytological 
examination showed that these gonads had the male comple- 
ment of chromosomes. In some way the primitive germ cells 
which formed the gonads failed to receive two x-chromosomes, 
and so testes developed instead of ovaries. That the soma was 
