sentinel an unmoulted or hard-shelled individual to prevent
marine enemies from injuring moulted individuals in their
unprotected state."(5)

Facts illustrating mutual aid amidst the termites, the ants,
and the bees are so well known to the general reader, especially
through the works of Romanes, L. Buchner, and Sir John Lubbock,
that I may limit my remarks to a very few hints.(6) If we take
an ants' nest, we not only see that every description of
work-rearing of progeny, foraging, building, rearing of aphides,
and so on--is performed according to the principles of
voluntary mutual aid; we must also recognize, with Forel, that
the chief, the fundamental feature of the life of many species of
ants is the fact and the obligation for every ant of sharing its
food, already swallowed and partly digested, with every member of
the community which may apply for it. Two ants belonging to two
different species or to two hostile nests, when they occasionally
meet together, will avoid each other. But two ants belonging to
the same nest or to the same colony of nests will approach each
other, exchange a few movements with the antennae, and "if one of
them is hungry or thirsty, and especially if the other has its
crop full... it immediately asks for food." The individual thus
requested never refuses; it sets apart its mandibles, takes a
proper position, and regurgitates a drop of transparent fluid
which is licked up by the hungry ant. Regurgitating food for
other ants is so prominent a feature in the life of ants (at
liberty), and it so constantly recurs both for feeding hungry
comrades and for feeding larvae, that Forel considers the
digestive tube of the ants as consisting of two different parts,
one of which, the posterior, is for the special use of the