ieties of the double
annual stock, from having been long and carefully selected to the right
degree, always produce a large proportion of seedlings bearing double
and quite sterile flowers, but they likewise yield some single and
fertile plants. These latter, by which alone the variety can be
propagated, may be compared with the fertile male and female ants, and
the double sterile plants with the neuters of the same community. As
with the varieties of the stock, so with social insects, selection has
been applied to the family, and not to the individual, for the sake
of gaining a serviceable end. Hence, we may conclude that slight
modifications of structure or of instinct, correlated with the sterile
condition of certain members of the community, have proved advantageous;
consequently the fertile males and females have flourished, and
transmitted to their fertile offspring a tendency to produce sterile
members with the same modifications. This process must have been
repeated many times, until that prodigious amount of difference between
the fertile and sterile females of the same species has been produced
which we see in many social insects.

But we have not as yet touched on the acme of the difficulty; namely,
the fact that the neuters of several ants differ, not only from the
fertile females and males, but from each other, sometimes to an almost
incredible degree, and are thus divided into two or even three castes.
The castes, moreover, do not generally graduate into each other, but are
perfectly well defined; being as distinct from each other as are any
two species of the same genus, or rather as any two genera of the same
family. Thus, in Eciton, there are working and soldier neuters, with
jaws and instincts extraordinarily different: in Cryptocerus, the
workers of one caste alone carry a wonderful sort of shield on their
heads, the use of which is quite unknown: in the Mexican Myrmecocystus,
the workers of one caste never leave the nest; they are fed by the
workers of another caste, and they have an enormously developed abdomen
which secretes a sort of honey, supplying the place of that excreted
by the aphides, or the domestic cattle as they may be called, which our
European ants guard and imprison.

It will indeed be thought that I have an overweening confidence in the
principle of natural selection, when I do not admit that such wonderful
and well-established facts at once annihilate the theory. In the simpler
c