SEXUAL CHARACTERISTICS OF THELIA 615 
female did not prevent the development of testes, nor did the 
presence of testes in any way interfere with the development of 
the female somatic characteristics. In insects the chromatin of 
the germ cells represents a mechanism for shaping the gametes, 
and this mechanism is extremely difficult to upset, and cannot 
be interfered with by metabolic changes in the soma. 
This is nicely demonstrated in parasitized male Thelia. Many 
careful microscopic examinations of some forty testes and rem- 
nants of testes from parasitized males have failed to reveal any 
cells taking on the characteristics of odcytes. That the metab- 
olism of these males was altered by the growing Aphelopus 
larvae cannot be in the least questioned. They were no longer 
animals of high oxidizing powers, but stored fat in large quan- 
tities and in many other ways approached female metabolism. 
Still spermatocytes failed to grow beyond their normal size, and 
often, when conditions were not too adverse, divided into sper- 
matids which differentiated into mature spermatozoa. Frequent- 
ly, fatty infiltration caused the spermatocytes to degenerate, 
and one might infer that conditions in parasitized individuals 
always made continued growth of the germ cells impossible. 
This, however, cannot be the case, for in parasitized females 
odcytes measuring 390u by 46. have been found, and these 
had grown in the adult females from cells no larger than 56u 
by 36, which is the maximum size of odcytes at the final 
molt. Therefore, storage is possible in the germ cells of para- 
sitized adults. But spermatocytes are not induced by changed 
conditions to approach in character the germ cells of the female, 
although the spermatogonia may have been subjected to the 
changed environment for many generations. That the gamete- 
forming mechanism is rather stable is shown also by Gold- 
schmidt’s intersexual moths (’17b). He states that the last 
organ to be changed to that of the opposite sex is the gonad. 
Likewise in vertebrates, where the development of the sexual 
characteristics is largely dependent on hormones, the gameto- 
cytes are not easily influenced. Thus in the gonads of the 
freemartins, although the general structure of the ovary is pro- 
foundly changed by the male hormones, still the germ cells fail 
