SEXUAL CHARACTERISTICS OF THELIA 599 
in ontogeny than do the ovaries, so that when the imaginal form 
is reached the testes have already reached their maximum size 
and contain mature sperm, whereas the ovaries are still very 
immature. This same discrepancy in rate of development may 
also be noted in the various nymphal instars. Thus in the. 
fourth instar of Thelia the testicular tubules average 0.2 mm. in 
length, whereas the terminal chambers of the ovaries average 
0.1 mm. in length. In the testis of the anomalous nymph: the 
tubules were on the average 0.15 mm. long, making the testes 
quite noticeably undersized. This would indicate that the 
rapid growth of the testes in normal males is not due entirely to 
the properties of the germ cells, but that the soma which pro- 
vides the nutriment contributes in no small measure to the 
growth of these cells. In this nymph with female soma the 
testes did not get all the nourishment they required, but prob- 
ably they did get more material for growth than is ordinarily 
supplied to an ovary at this stage. The lack of sufficient nutri- 
ment evinced itself in the presence of many cysts of degenerating 
spermatogonia, such as may often be found in mature testes, 
but not in normal testes of nymphs. Previously (Kornhauser, 
14, p. 251) it was suggested that the degeneration of cysts of 
spermatogonia, found so often just at the close of the period of 
multiplication in testicular tubules, was due to the lack of suffi- 
cient cytoplasmic materials, and the present case seems to bear 
out this presumption. 
The conclusions we may draw from the two significant individ- 
uals described in the previous pages are: that the development 
of the female soma of Thelia is not influenced by the presence of 
gonads of the opposite sex; that the changes in parasitized male 
Thelia are not due to the absence of testicular tissue, and that 
the development of the gonad into ovary or testis is primarily 
determined by the chromosomal composition of its cells, but the 
growth of the testis is in part dependent upon the soma which 
nourishes the germ cells. 
