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XXIV. On the sexes of larve emerging from the succes- 
sively laid eggs of Smerinthus populi. By Hpwarp 
B. Povutron, M.A., F.R.S., F.L.8., &c., Hope Pro- 
fessor of Zoology in the University of Oxford. 
[Read November 8th, 1893. | 
My friend and former pupil, Mr. R. C. L. Perkins, once 
told me that he had sometimes noticed that a pair of 
Sphinx larve found in the same stage of growth, in close 
proximity upon the same tree, and presumably hatched 
from a pair of eggs laid by the same parent, produce 
moths of different sexes. He inferred that this arrange- 
ment facilitated pairing, and he was led to wonder 
whether there is a regular alternation of sex in the 
successive offspring. 
On the other hand, it appeared quite possible that the 
cases which he had observed were exceptional, and that 
the succession is irregular, or that it is such as to 
facilitate intercrossing rather than frequent pairing be- 
tween closely related individuals. This latter view is 
suggested asa probable one by the numerous adaptations 
by which wide intercrossing is favoured in other depart- 
ments of organic nature, and by the following direct 
evidence. Mr. W. Hatchett Jackson and Mr. O. H. 
Latter have observed that the pup obtained from diffe- 
rent batches of larve of Vanessa io ‘‘ were principally, 
but not entirely, of one or of the other sex.” * It is 
generally admitted that the separate colonies of Vanessa 
larve are, at any rate as a rule, hatched from different 
batches of eggs. Such an observation, if confirmed, is 
to be interpreted by one of two suppositions. We 
must either suppose that the whole mass of eggs of 
each female Vanessa produces a great preponderance of 
one and the same sex (males in some individuals and 
females in others), or that different batches of eggs laid 
* Trans. Linn. Soc. Lond., vol. v., 1890, p. 156. 
TRANS. ENT. SOC. LOND. 1893.—paRT IV. (DEC.) 
