In the sting which they give to the nerve-centres of
their victim, in order to destroy its power of moving without killing
it, these different species of hymenoptera take into account, so to
speak, the different species of prey they respectively attack. The
Scolia, which attacks a larva of the rose-beetle, stings it in one point
only, but in this point the motor ganglia are concentrated, and those
ganglia alone: the stinging of other ganglia might cause death and
putrefaction, which it must avoid.[70] The yellow-winged Sphex, which
has chosen the cricket for its victim, knows that the cricket has three
nerve-centres which serve its three pairs of legs--or at least it acts
as if it knew this. It stings the insect first under the neck, then
behind the prothorax, and then where the thorax joins the abdomen.[71]
The Ammophila Hirsuta gives nine successive strokes of its sting upon
nine nerve-centres of its caterpillar, and then seizes the head and
squeezes it in its mandibles, enough to cause paralysis without
death.[72] The general theme is "the necessity of paralyzing without
killing"; the variations are subordinated to the structure of the victim
on which they are played. No doubt the operation is not always perfect.
It has recently been shown that the Ammophila sometimes kills the
caterpillar instead of paralyzing it, that sometimes also it paralyzes
it incompletely.[73] But, because instinct is, like intelligence,
fallible, because it also shows individual deviations, it does not at
all follow that the instinct of the Ammophila has been acquired, as has
been claimed, by tentative intelligent experiments. Even supposing that
the Ammophila has come in course of time to recognize, one after
another, by tentative experiment, the points of its victim which must be
stung to render it motionless, and also the special treatment that must
be inflicted on the head to bring about paralysis without death, how can
we imagine that elements so special of a knowledge so precise have been
regularly transmitted, one by one, by heredity? If, in all our present
experience, there were a single indisputable example of a transmission
of this kind, the inheritance of acquired characters would be questioned
by no one. As a matter of fact, the hereditary transmission of a
contracted habit is effected in an irregular and far from precise
manner, supposing it is ever really effected at all.

But the whole difficulty comes from our desire to expres