nd excreted a limpid drop
of sweet juice, which was eagerly devoured by the ant. Even the quite
young aphides behaved in this manner, showing that the action was
instinctive, and not the result of experience. It is certain, from the
observations of Huber, that the aphides show no dislike to the ants:
if the latter be not present they are at last compelled to eject their
excretion. But as the excretion is extremely viscid, it is no doubt a
convenience to the aphides to have it removed; therefore probably they
do not excrete solely for the good of the ants. Although there is no
evidence that any animal performs an action for the exclusive good of
another species, yet each tries to take advantage of the instincts of
others, as each takes advantage of the weaker bodily structure of other
species. So again certain instincts cannot be considered as absolutely
perfect; but as details on this and other such points are not
indispensable, they may be here passed over.

As some degree of variation in instincts under a state of nature, and
the inheritance of such variations, are indispensable for the action of
natural selection, as many instances as possible ought to be given; but
want of space prevents me. I can only assert that instincts certainly
do vary--for instance, the migratory instinct, both in extent and
direction, and in its total loss. So it is with the nests of birds,
which vary partly in dependence on the situations chosen, and on the
nature and temperature of the country inhabited, but often from causes
wholly unknown to us. Audubon has given several remarkable cases
of differences in the nests of the same species in the northern and
southern United States. Why, it has been asked, if instinct be variable,
has it not granted to the bee "the ability to use some other material
when wax was deficient?" But what other natural material could bees
use? They will work, as I have seen, with wax hardened with vermilion
or softened with lard. Andrew Knight observed that his bees, instead of
laboriously collecting propolis, used a cement of wax and turpentine,
with which he had covered decorticated trees. It has lately been shown
that bees, instead of searching for pollen, will gladly use a very
different substance, namely, oatmeal. Fear of any particular enemy is
certainly an instinctive quality, as may be seen in nestling birds,
though it is strengthened by experience, and by the sight of fear of the
same enemy in other animal