414 Experimental Zoology 
sperm, one of them functionless, etc. It is apparent, therefore, 
that Beard’s theory resolves itself into two assumptions: first, that 
sex is determined by the egg alone; and secondly, that two kinds 
of eggs are produced. The solution of the problem is merely 
shifted to a new field, since it is assumed that the male and female 
eggs are produced, and no explanation of how or when this occurs 
is forthcoming. 
Beard’s view encounters, moreover, special difficulties that 
can only be explained away by further assumptions. For ex- 
ample, in the aphids there is a long succession of female partheno- 
genetic eggs, ending finally in the production of male and female 
parthenogenetic eggs. It would seem that external conditions 
must determine whether the eggs are to be all female eggs or 
some male and some female, but there is nothing in Beard’s 
theory that indicates how such a thing is possible. 
In the case of the bee, Beard is forced into the position of as- 
suming that the sex of the individual is not dependent on whether 
it is or is not fertilized, although the clearest evidence that we 
have points unmistakably in that direction. He argues that 
only female eggs can be fertilized, while male eggs cannot be 
fertilized; but if this were the case, it is not evident how the 
queen could distinguish between the two kinds of eggs and lay 
each in its appropriate cell. 
Castle has also proposed a hypothesis of ‘The Heredity of 
Sex.” His hypothesis is avowedly an attempt to account for 
the determination of sex by means of the Mendelian method. - 
It had already been suggested by Strasburger and by Bateson 
that the sexual forms might bear the same relation to each 
other as do the offspring of Mendelian hybrids. Castle has 
elaborated this idea into an ingenious hypothesis. He assumes 
that there are two kinds of spermatozoa, male and female; 
and two kinds of eggs, male and female. If we assume, as 
in the case of Mendelian hybrids, that all possible chance 
combinations occur between the germ-cells, we should expect 
three kinds of individuals (as in the Mendelian proportion), — 
males, females, and hermaphrodites. There would be as many 
