SEXUAL CHARACTERISTICS OF THELIA 539 
of the chromosomes introduced by the spermatozoon. Sex inter- 
grades, which are generally mosaics of the soma of both sexes, often 
containing abnormal gonads of hermaphroditic character, have 
been studied by Goldschmidt (’16, °17 b) in the moth Lyman- 
tria, and by Banta (716) in the crustacean Simocephalus. Al- 
though these forms, as in the case of gynandromorphs, support 
the idea that the somatic cells are physiologically independent 
of the gonads in development, still the explanation of these 
mosaics on a cytological basis must await further investigation 
of their chromosomal make-up. Banta believes the environment 
plays an important réle, whereas Goldschmidt (17 b), although 
believing in a chromosomal explanation, is skeptical of obtain- 
ing a visible demonstration of size differences of chromatic 
elements in the components of the mosaics of Lepidoptera. 
Although the sexual characteristics seem to be fixed, there are 
nevertheless three lines of evidence which indicate that in every 
normal individual the determinants for the opposite sex are 
present in a hidden condition. First, the males may be pro- 
duced by parthenogenesis, as is the case in the rotifers, in many 
Entomostraca, and in numerous insects, especially homopterans 
and hymenopterans, also occasionally in Lepidoptera and arti- 
ficially induced in frogs (Loeb, ’16, Gatenby, 17). The mechan- 
ism of parthenogenetic male production has been most fully 
solved in the aphids (von Baehr, ’09) and in the phylloxerans 
(Morgan, 09). That the egg before maturation is equivalent to 
the genetic constitution of the cells of the female which produced 
it is agreed upon by all biologists. In the production of a male 
from such an unfertilized egg, something must be eliminated to 
allow the hidden male characters to appear. Thus Morgan and 
von Baehr have shown that there is a differential maturation and 
that every small (male) egg throws off a whole x-chromosome or 
a group of x-chromosomes in the polar body. We can hardly 
escape from the belief that the presence or the absence of a par- 
ticular x-chromosome determines whether the male or the female 
characteristics shall develop in the mature egg. ‘The size of the 
egg, however, regulates the maturation, so it seems; since the 
small eggs always extrude one x-chromosome or one group of 
