The Determination of Sex 373 
of the eggs (those that formerly produced males, let us say) 
are present and fail to develop. The alternative view seems 
more plausible, that all the eggs produce females. If this view 
is the correct one, then we find that in parthenogenetic species 
two changes have occurred, all the eggs produce females, and 
at the same time these female eggs have acquired the power to 
develop without fertilization. It may be that both processes 
have gone on hand in hand, and the same tendency to develop 
parthenogenetically is associated with a tendency to produce 
only females. In not a single case has the sex of the embryo, 
produced by artificial means, been determined, therefore we 
lack experimental evidence to form any opinion on this point. 
In species where occasional parthenogenesis occurs both male 
and female individuals may develop from unfertilized eggs, as 
in the silkworm moth. In other groups apparently more females 
develop, as in certain other moths, but in these the process of 
parthenogenesis is sometimes quite regular rather than occa- 
sional. In the honey bee and in some other hymenoptera, 
males as a rule develop from parthenogenetic eggs. 
Whatever conclusion we reach finally in regard to the origin 
of parthenogenetic species, one point must be always borne in 
mind: parthenogenetic eggs carry latent, or in a potential con- 
dition, the male characters which may at any time become domi- 
nant. There are certain species that produce only partheno- 
genetic females in one generation, but males and females in 
approximately equal numbers may appear in the next generation, 
as in the gallflies; and in other species that have a long succes- 
sion of parthenogenetic females, males and sexual females may 
appear in at least equal numbers. These cases seem to indicate 
with some probability that parthenogenesis has not arisen by the 
suppression of the male eggs, but by the dominance of the female 
characters in all of the eggs. What is true for the so-called female 
eggs is probably also true for the male-producing eggs in uni- 
sexual forms. The male egg carries latent the characters of 
the female, and the hereditary transmission by means of the male 
of the maternal characters shows that this must be the true view. 
