360 Life-history of Melittobia acasta 
Coitus is very rapid and the male immediately seeks for another mate. 
He quickly decides whether a female is willing or unwilling and wastes very 
little time over the latter. 
VII. The Numerical Proportion of the Sexes. 
There seems to be no reliable way of determining the proportion of the 
sexes in a family, since the male and female eggs are indistinguishable, as 
I have already said, and the larvae are more or less cannibals, so that some¬ 
times quite large numbers of individuals disappear during the larval period. 
By counting pupae one gets more reliable results than by counting the imagines 
since the males in the latter stage destroy one another, and, under laboratory 
conditions, also sometimes destroy females. 
Graham Smith gives results of counts of imagines which range from less 
than one to more than fifty males per hundred females but, since a female 
may lay more than a thousand eggs and his figures are all for small batches, 
they give us no reliable criterion. 
By counting pupae I found that, in any one batch of eggs, the males ran 
from about one to four or five per cent, of the females. 
Now, as will be shown later, a female normally lays two, and perhaps 
three, batches of eggs and she mates with a male before each bout of egg- 
laying. If she is unfertilized or if, after laying a batch of eggs she is not 
permitted to mate again, she can only lay male eggs, that is, the eggs can only 
develop into males. Presumably therefore unfertilized eggs produced males 
and fertilized produce females, as in many other Hymenoptera. As therefore 
she produces both male and female offspring after mating and before she has 
exhausted her supply of spermatozoa, it is reasonable to conclude that she 
can control the flow of spermatozoa from her spermotheca and thus determine 
the sex of her offspring—as Fabre has shown is the case with certain species 
of Osmia and Chalicodoma ( v . Bramble Bees and Others , Chaps. IV and ). 
It might also be concluded from the fact that males usually emerge first in 
a brood, that the first eggs laid by the female are male eggs, but it may be that 
males develop more rapidly than females, a point I have so far omitted to 
investigate. 
If therefore the sex is determined by the mother at the time of oviposition 
the proportion may well vary for each female according to circumstances. 
VIII. Fecundity. 
I have already mentioned that oviposition may commence within twenty- 
four hours of the emergence of the female but it is often, perhaps usually, 
a very prolonged process. 
Malyshev states that the females lay 200 to 300 eggs and perhaps more 
during four or five weeks but he does not say how he obtained his figures. 
I have, however, obtained results in my experiments which seem to indicate 
that the females are much more prolific than this author has shown. 
