456 Sexes of larve of Smerinthus populi. 
the struggle with highly organised enemies in deter- 
mining the vast amount of destruction which occurs 
among these animals in the natural state. 
The unfortunate loss of the 47 larve of May 26th 
served to show that the period of development within 
the ege is extremely uniform. The eges laid on May 
25th had been properly enclosed, and I thought I was safe 
in leaving the others for a day. On my return every 
one of the eggs laid on the 26th had hatched, and the 
larvee had escaped; while not a single larva had emerged 
from any egg laid at a later date. 
Six of the male pups were deformed, but not one of 
the females. 
The total number of eggs laid was 198, and subsequent 
dissection revealed a single egg in the body of the 
parent moth. From these eggs 68 female and 59 male 
pupe were obtained. 
The results afford no support to the opinion that the 
sex of insects can be determined by external conditions 
during larval life. With conditions of very complete 
uniformity, the proportions of the sexes—68 females to 
59 males—appear to be normal. It may be admitted 
that the larger female larvee require more food, chiefly 
to prepare for the amount of material to be stored up in 
the ova. It would not therefore be at all surprising if 
the female larvee were starved before the males when a 
minimum of food was supplied. The consequent emer- 
gence of a number of males would in no way support the 
view that a scanty diet ‘“‘determines” this sex. It is 
probable that some writers on this subject have mistaken 
favouring for determining conditions. 
There was no tendency towards the predominance of 
males in the last-laid eggs, and therefore no indication 
that this sex may be determined by exhaustion (in itself 
most improbable) of the spermatozoa. 
