SEXUAL CHARACTERISTICS OF THELIA 625 
as it comes into activity must cause a change in the protoplasmic 
mass which it influences and, since the cells are not independent 
but in physiological continuity, this constitutes a definite step 
also. Since each gene is represented in every cell of the indi- 
vidual, its coming into particular activity in one part of the 
organism might be accompanied by minor changes due to this 
same gene in other parts of the organism. In both arthropods 
and vertebrates I would look upon the sexual development of 
the individual as a continuous series, each step depending on the 
steps preceding. The presence of one x-chromosome would 
form the basis for the inauguration of the male series, beginning 
in the formation of a sperm-forming gonad and ending with the 
production of specific secondary sexual characteristics. Like- 
wise, the presence of two x-chromosomes in the zygote would 
start the female series of developmental changes. 
Returning finally to the effect of Aphelopus upon Thelia 
bimaculata, will the foregoing considerations help us any in 
understanding the changes suffered especially by the male in its 
secondary sexual characteristics? It was shown that the germ 
cells of the male were not changed toward those of the female 
type, nor were the male gonapophyses altered so as to be sim- 
ilar to those of the female, although they were reduced in size. 
These reduced external genitalia, although still retaining the 
general form common to the membracids, lost their specific 
characteristics. In the fifth instar it was noted that parasitized 
individuals of both sexes showed a retardation in the develop- 
ment of the gonapophyses. The striking changes brought about 
were in those characteristics of the male which first appear at 
the final molt and belong to the category of the extragenital 
characteristics. Especially noteworthy was the loss of the male 
coloration and the assumption of the female pigment and pat- 
tern. Likewise, the female arrangement of the spines on the 
abdominal sclerites and increase in size of all parts of the body 
were plainly observed in parasitized males. It must also be 
remembered that parasitized males formed a complete series 
from those but slightly altered to those with extreme change. 
Those but slightly changed, if taken shortly after the final molt, 
