620 SIDNEY I. KORNHAUSER 
If the production of an animal with but one active x-chromo- 
some had as its consequence, perhaps through further muta- 
tions in the one-x-individual, the formation of a microgamete- 
producing individual, the beginning of sexual differentiation 
would be established. The inactivation of the x-chromosome or 
the production of the y-chromosome may merely have brought 
about a less stable condition in the cells of the individual possess- 
ing the inactive x-element, and offered a basis for further muta- 
tions leading to the differentiation of two types of individuals, 
one producing microgametes and the other macrogametes. 
The further divergence of the sexes in the form of the gametes 
and soma would be partially dependent upon this primary 
difference in stability or constitution, for new genes would 
necessarily arise and be expressed either in cells with one or 
with two functional x-chromosomes. That there is something 
vital in the x-chromosome upon which development depends 
was shown nicely by Bridges, who proved that zygotes without 
an x-chromosome or with more than two x-chromosomes failed 
to develop. It is therefore not unlikely that cells having two 
sets of x-genes should be somewhat differently constituted than 
those possessing but a single set. ‘The male often shows a much 
greater tendency toward variation than does the female, and 
this most probably is referable to a greater conservativeness in 
the composition of the female cells. In the family of the Mem- 
bracidae, with which the author is fairly familiar, the variability 
of the males is much greater than that of the females. In Thelia 
the form of the pronotal horn and the extent of the vitta, as 
illustrated in figure 7, page 556, exhibit far less constancy than 
in the female. Fowler (’08) has described and figured many 
types of the membracid Umbonia orozimba which in the male 
show many types of variations in color, form, and size. Some 
greatly resemble the females, but the series extends to forms so 
unlike the female that they were originally placed in another 
genus, Physoplia, by Amyot and Serville (’43). As stated on 
page 589, the membracids are characterized by conservativeness 
of the genital appendages. Lately the author has studied the 
genitalia of both sexes of forms from the various subfamilies 
