438 Evolution and Adaptation ’ 
Castle assumes, in fact, that in animals like daphnids and 
rotifers one polar body only is extruded, and the other (the 
second) is retained in the egg, and hence the potentiality of 
producing males is present. In the honey-bee, on the con- 
trary, Castle assumes that both polar bodies are extruded 
in the unfertilized egg (and there are some observations that 
support this idea), and since only males are produced from 
these, he believes it is the female element that has been sent 
out into the second polar body. This hypothesis is necessary, 
because Castle assumes that when both elements are pres- 
ent in the bee’s eggs, the female element dominates. ‘“ Hence, 
if the egg which has formed two polar cells develops with- 
out fertilization, it must develop into a male. But if such an 
egg is fertilized, it invariably forms a parthenogenetic female 
?(o), that is, an individual in which the male character is 
recessive. Accordingly the functional spermatozoon must 
in such cases invariably bear the female character, and this is 
invariably dominant over the male character when the two 
meet in fertilization.” 
If it should prove generally true that the size of the egg 
is one of the factors determining the sex, we have still the 
further question to consider as to whether some eggs are 
bigger because they are already female, or whether all eggs 
that go beyond a certain size are females, and all those that 
fail to reach this are males. If this is the case, an animal 
might produce more females if the external conditions were 
favorable to the growth of the eggs, and if in some cases 
these large eggs were capable of developing, parthenogenetic 
races might become established. Should, however, the condi- 
tions for nutrition become less favorable, some of the eggs 
might fall below the former size and produce males. It is 
not apparent, however, why all the fertilized autumn eggs of 
the aphids should give rise to females, for although these 
eggs are known to be larger than the summer eggs, yet they 
are produced under unfavorable conditions. 
