10.]

[Illustration: FIG. 11.]

The provisions collected by these two birds reveal a remarkable fact.
They possess indeed two distinct diets; they do not preserve for the
period of famine the overplus of the foods which they consume in the
period of abundance. They chase insects and feed on them as long as
they can find them, while they gather up in their storehouses an
entirely different food.

_Physiological reserves._--All the animals of which I have just spoken
place their provisions for the future in barns in the same manner as
Man. Those who have not this foresight are either able to nourish
themselves in all seasons by the chase, or else, after having feasted
one half of the year, they fast during the other half. In the latter
case they consume during the fasting period a portion of their own
substance, and use up materials placed in reserve in their organism,
in the form of fat for example. This arrangement, which allows them to
prolong life, though growing thin, until the next season of
prosperity, is not under the control of the will. It is a complication
of physiological phenomena resulting from the functioning of different
parts of the organism.

_Stages between physiological reserves and provisions._--Between
physiological reserves and industrial stores we may place as an
intermediate stage the interesting case of the Honey Ants.[53]

[53] H. C. McCook, _The Honey Ants of the Garden of the
Gods, and the Ants of the American Plains_, Philadelphia,
1882.

[Illustration: FIG. 12.]

[Illustration: FIG. 13.]

These insects (_Myrmecocystus_) live in Texas, and form colonies in
which certain individuals play a very special part They exaggerate to
an extreme point the power of preserving provisions in their crops.
These materials are not assimilated; they do not form part of the
animal's body, and although placed inside it cannot be compared to
physiological reserves. It is especially curious that they are not to
be utilised only by the animal itself, but also by the other members
of the colony who are not able to form such stores. Among the
_Myrmecocystus_ there are workers of two sorts; the first kind
resemble other ants with some differences of detail, and build and
hollow the earth nest which shelters the community. The second kind is
quite different; the abdomen in these workers is enormously distended
so as to constitute a voluminous sphere, which may become four or five
times