532 SIDNEY I. KORNHAUSER 
Let us first define the characteristics which distinguish male- 
ness from femaleness. The male germ gland produces sperm 
cells, the female produces eggs, and that certainly is the primary 
difference. But in addition there are sexual differences in the 
soma and these are striking in the group of insects under con- 
sideration. These somatic differences are generally designated 
as secondary sexual characteristics. ‘They may be divided into 
two categories: those immediately concerned with the transfer 
of the spermatozoa or the laying of the egg may be called genital 
secondary characteristics, and those differences in color, orna- 
mentation, and general form of body may be called extragenital 
secondary sexual characteristics or, if one choose, tertiary sexual 
differences. One of the problems, stimulated by remarkable 
results in the vertebrates, has been to determine in the insects, 
whether or not the development of the somatic sexual differ- 
ences is dependent upon or independent of the primary sex gland. 
Attempts to alter these secondary and tertiary characteristics 
of insects by experimental castration or the transplantation of 
gonads have not proved successful: the soma seems to be fixed, 
either male or female, and not dependent for its development 
upon the gonad nor upon some hormone developed by the gonad. 
We have, therefore, no means, except through hybridization, 
under our direct control of determining whether or not the 
secondary sexual characteristics of the opposite sex may be 
present in a latent form in either male or female insect. Cer- 
tainly, latent characteristics cannot be brought out, as they may 
be in birds and mammals, by removal or transplantation of the 
gonads. Accordingly, it is of interest to observe the results of 
an experiment in nature in which the seemingly fixed and strik- 
ing sexual characteristics of the male insect have been lost and 
those of the female have appeared in their place; this change 
being brought about by the action of internal hymenopteron 
parasites. 
In the summer of 1911, while collecting Thelia at Cold Spring 
Harbor for a cytological study, the writer was struck with the 
fact that more gray females were to be seen on the locust trees 
than handsome brown and yellow males, and this in midseason, 
