have been disused as far as its glandular portion and its stalk are
concerned, and also of the wings, the nerves tracheae and epidermal
cells of which could not cease to function until the whole wing had
degenerated, for the chitinous skeleton of the wing does not function
at all in the active sense.

But, on the other hand, the workers in all species have undergone
modifications in a positive direction, as, for instance, the greater
development of brain. In many species large workers have evolved,--the
so-called _soldiers_, with enormous jaws and teeth, which defend the
colony,--and in others there are _small_ workers which have taken over
other special functions, such as the rearing of the young Aphides.
This kind of division of the workers into two castes occurs among
several tropical species of ants, but it is also present in the
Italian species, _Colobopsis truncata_. Beautifully as the size of the
jaws could be explained as due to the increased use made of them by
the "soldiers," or the enlarged brain as due to the mental activities
of the workers, the fact of the infertility of these forms is an
insurmountable obstacle to accepting such an explanation. Neither jaws
nor brain can have been evolved on the Lamarckian principle.

The problem of coadaptation is no easier in the case of the ant than
in the case of the Giant Stag. Darwin himself gave a pretty
illustration to show how imposing the difference between the two kinds
of workers in one species would seem if we translated it into human
terms. In regard to the Driver ants (Anomma) we must picture to
ourselves a piece of work, "for instance the building of a house,
being carried on by two kinds of workers, of which one group was five
feet four inches high, the other sixteen feet high."[39]

Although the ant is a small animal as compared with man or with the
Irish Elk, the "soldier" with its relatively enormous jaws is hardly
less heavily burdened than the Elk with its antlers, and in the ant's
case, too, a strengthening of the skeleton, of the muscles, the nerves
of the head, and of the legs must have taken place parallel with the
enlargement of the jaws. _Harmonious adaptation_ (coadaptation) has
here been active in a high degree, and yet these "soldiers" are
sterile! There thus remains nothing for it but to refer all their
adaptations, positive and negative alike, to processes of selection
which have taken place in the rudiments of the workers within the e