w nest shall be formed, and when they migrate,
the masters carry the slaves. Both in Switzerland and England the slaves
seem to have the exclusive care of the larvae, and the masters alone go on
slave-making expeditions. In Switzerland the slaves and masters work
together, making and bringing materials for the nest: both, but chiefly the
slaves, tend, and milk as it may be called, their aphides; and thus both
collect food for the community. In England the masters alone usually leave
the nest to collect building materials and food for themselves, their
slaves and larvae. So that the masters in this country receive much less
service from their slaves than they do in Switzerland.

By what steps the instinct of F. sanguinea originated I will not pretend to
conjecture. But as ants, which are not slave-makers, will, as I have seen,
carry off pupae of other species, if scattered near their nests, it is
possible that such pupae originally stored as food might become developed;
and the foreign ants thus unintentionally reared would then follow their
proper instincts, and do {224} what work they could. If their presence
proved useful to the species which had seized them--if it were more
advantageous to this species to capture workers than to procreate them--the
habit of collecting pupae originally for food might by natural selection be
strengthened and rendered permanent for the very different purpose of
raising slaves. When the instinct was once acquired, if carried out to a
much less extent even than in our British F. sanguinea, which, as we have
seen, is less aided by its slaves than the same species in Switzerland, I
can see no difficulty in natural selection increasing and modifying the
instinct--always supposing each modification to be of use to the
species--until an ant was formed as abjectly dependent on its slaves as is
the Formica rufescens.

_Cell-making instinct of the Hive-Bee._--I will not here enter on minute
details on this subject, but will merely give an outline of the conclusions
at which I have arrived. He must be a dull man who can examine the
exquisite structure of a comb, so beautifully adapted to its end, without
enthusiastic admiration. We hear from mathematicians that bees have
practically solved a recondite problem, and have made their cells of the
proper shape to hold the greatest possible amount of honey, with the least
possible consumption of precious wax in their construction. It has been
remark