The workers in the various species of ants are sterile, that is to say,
they take no regular part in the reproduction of the species, although
individuals among them may occasionally lay eggs. In addition to this they
have lost the wings, and the receptaculum seminis, and their compound eyes
have degenerated to a few facets. How could this last change have come
about through disuse, since the eyes of workers are exposed to light in the
same way as are those of the sexual insects and thus in this particular
case are not liable to "disuse" at all? The same is true of the
receptaculum seminis, which can only 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