difficulty: he finds that all the Lampyridae which he has tried are
highly distasteful to insectivorous mammals and birds. Hence it is in
accordance with Mr. Bates view, hereafter to be explained, that many
insects mimic the Lampyridae closely, in order to be mistaken for them,
and thus to escape destruction. He further believes that the luminous
species profit by being at once recognised as unpalatable. It is
probable that the same explanation may be extended to the Elaters, both
sexes of which are highly luminous. It is not known why the wings of
the female glow-worm have not been developed; but in her present state
she closely resembles a larva, and as larvae are so largely preyed on
by many animals, we can understand why she has been rendered so much
more luminous and conspicuous than the male; and why the larvae
themselves are likewise luminous.
DIFFERENCE IN SIZE BETWEEN THE SEXES.
With insects of all kinds the males are commonly smaller than the
females; and this difference can often be detected even in the larval
state. So considerable is the difference between the male and female
cocoons of the silk-moth (Bombyx mori), that in France they are
separated by a particular mode of weighing. (13. Robinet, Vers a
Soie, 1848, p. 207.) In the lower classes of the animal kingdom, the
greater size of the females seems generally to depend on their
developing an enormous number of ova; and this may to a certain extent
hold good with insects. But Dr. Wallace has suggested a much more
probable explanation. He finds, after carefully attending to the
development of the caterpillars of Bombyx cynthia and yamamai, and
especially to that of some dwarfed caterpillars reared from a second
brood on unnatural food, that in proportion as the individual moth is
finer, so is the time required for its metamorphosis longer; and for
this reason the female, which is the larger and heavier insect, from
having to carry her numerous eggs, will be preceded by the male, which
is smaller and has less to mature. (14. Transact. Ent. Soc. 3rd
series, vol. v. p. 486.) Now as most insects are short-lived, and as
they are exposed to many dangers, it would manifestly be advantageous
to the female to be impregnated as soon as possible. This end would be
gained by the males being first matured in large numbers ready for the
advent of the females; and this again would naturally follow, as Mr.
A.R. Wallace has remarked (15. Journal of Proc. Ent. Soc. Feb. 4,
1867, p. lxxi.), through natural selection; for the smaller males would
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