SEXUAL CHARACTERISTICS OF THELIA 631 
external examination of the nymphal gonapophyses of the third 
instar and by an examination of sections much earlier than this. 
These genital appendages are ancient ontogenetically and phylo- 
genetically as well, belonging to a type primitive for the group 
of the Homoptera. The small parasites of the younger instars 
are not capable of changing the growing sexually differentiated 
nymphal gonapophyses to those of the opposite sex. They may 
retard the development of these appendages in both sexes, so 
that fifth instars with full-grown parasites present gonapophyses 
quite similar to those found in fourth instars. 
11. The parasites generally cause the degeneration of the 
gonads and bring about an accumulation of fat in the abdomen 
of the host. Testes and ovaries in various stages of disappear- 
ance were studied. Never were cells similar to odcytes found 
in any testes, but normal spermatogenesis proceeded as far as 
possible under adverse conditions. Likewise, odcytes retained 
their characteristic features and even grew for a time in some 
parasitized adult females. 
12. One parasitized male was found which, although con- 
siderably changed toward the female condition, contained a 
full-sized normal testis with many spermatozoa. Another in- 
dividual, a fourth instar, showed perfect female soma, but con- 
tained male gonads composed of cells with the characteristic 
male complex of chromosomes. The first individual indicates 
that the changes wrought by the parasites are not due directly 
to the destruction of the gonads, while the second individual 
lends support to the idea that the soma of arthropods is inde- 
pendent of the gonads in its development. Likewise, there is 
no evidence that the demand for food made by the parasites on 
the soma of male hosts stimulates the development of female 
secondary sexual characteristics. Such a demand has been 
assumed by other investigators to emanate normally from the 
ovaries, calling forth the development of the female characteristics. 
13. It is not thought probable that the lowering of the meta- 
bolic level in parasitized males could account for the®hanges 
described. 
