SEXUAL CHARACTERISTICS OF THELIA 603 
internal combinations may be associated with a bisexual soma. 
Likewise, such an anomalous individual as the Thelia nymph 
shown in figures 52 to 54 is most convincing proof that the testes 
produce no hormone which influences somatic development. 
In this individual, a nymph of the fourth instar with soma of a 
female and gonads of a male, the female secondary sexual 
characteristics were perfectly formed. Had the same conditions 
existed in this Thelia nymph as exists in developing vertebrates 
(Lillie, 17), the testes even though immature would have greatly 
modified the female somatic characteristics. It seems, there- 
fore, most probable that, in the insects and probably in the 
arthropods in general, the development of the secondary sexual 
characteristics is independent of the gonads. If we accept this, 
it follows that the effects of parasitism upon the sexual charac- 
teristics cannot be traced directly to the destruction of the 
gonads. 
A second objection to the term ‘castration parasitaire’ as a 
descriptive term for the effect of parasites on arthropod hosts is 
the fact that often the gonads are not wholly destroyed. Smith 
(10) showed that if the parasitic barnacle were removed from 
the host, the germinal epithelium might regenerate and produce 
germ cells which however in the male might grow into oécytes, 
instead of spermatocytes. In bees parasitized by Stylopidae the 
gonads of the male may still be functional, but in all cases the 
ovaries are described as being very minute. In Thelia generally 
the presence of large Aphelopus larvae had as its accompanying 
condition the entire absence of gonads. Nevertheless, occasion- 
ally in males remnants of testes were found, varying from minute 
clumps of germ cells imbedded in a mass of fatty tissue, to a 
full-sized testis, such as was shown in figure 50. In parasitized 
females minute ovaries were at times discovered. The largest 
odcytes found in such ovaries were 0.4 mm. in length. That a 
full-sized testis appearing normal in every way and filled with 
sperm was found in a parasitized male showing considerable 
somatic alteration is, I believe, convincing proof that the somatic 
changes found in parasitized male Thelia are not due to the 
absence of testicular tissue. 
