eparate at base
to form a sucking tube, while in others the maxillae are curved, and meet
to form a true tube.

[Illustration: 210. Mouth-parts of the House fly.]

[Illustration: 211. Mouth-parts of Horse fly.]

[Illustration: 212. Head of Humble bee.]

[Illustration: 213. Mouth-parts of Moths.]

In the Cecropia moth it is difficult to trace the rudiments of the
maxillae at all, and thus we have in the whole range of the moths, every
gradation from the wholly aborted maxillae of the Platysamia Cecropia, to
those of Macrosila cluentius of Madagascar, which form a tongue,
according to Mr. Wallace, nine and a quarter inches in length, probably
to enable their owner to probe the deep nectaries of certain orchids.
These changes in form and size are certainly correlated with important
differences in habits, and the evolutionist can as rightly say that the
structural changes were induced by use and disuse and change of habits
and the environment of the animal, as on the other hand the advocate of
special creation claims that the two are simply correlated, and that is
all we know about it.

[Illustration: 214. Ichneumon Fly.]

Another set of organs, placed on quite another region of the body, unite
to form the sting of the bee, or its equivalent the ovipositor of other
hymenopterous insects, such as the Ichneumon fly (Fig. 214), the "saw"
of the saw fly, and the augur of the Cicada. These are all formed on the
same plan, arising early in the larval stage as three pairs of little
tubercles, which ultimately form long blades, the innermost constituting
the true ovipositor. We have found that one pair of these organs forms
the "spring" of the Podura, and that in these insects it is three
jointed, and thus is morphologically a pair of legs soldered together at
their base. We would venture to regard the ovipositor of insects as
probably representing three pairs of abdominal legs, comparable with
those of the Myriopods, and even, as we have suggested in another place,
the three pairs of jointed spinnerets of spiders. Thus the ovipositor of
the bee has a history, and is not apparently a special creation, but a
structure gradually developed to subserve the use of a defensive organ.

So the organs of special sense in insects are in most cases simply
altered hairs. The hairs themselves are modified epithelial cells. The
eyes of insects, simple and compound, are at first simply epithelial
cells, modified for a special purpose, an