Contributions to the theory of natural selection. A series of essays ... By Alfred Russel Wallace ...

132 THE MALAYAN PAPILIONIrlDEi AS
members exhibit no appreciable change. The wings
of Butterflies, as Mr. Bates has well put i t, "serve
as a tablet on which Nature writes the story of the
modifications of species;" they enable us to perceive
changes that would otherwise be uncertain and difficult of observation, and exhibit to us on an enlarged
scale the effects of the climatal and other physical
conditions which influence more or less profoundly
the organization of every living thing.
A proof that this greater sensibility to modifying
causes is not imaginary may, I think, be drawn from
the consideration, that while the Lepidoptera as a
whole are of all insects the least essentially varied in
form, structure, or habits, yet in the number of their
specific forms they are not much inferior to those
orders which range over a much wider field of nature,
and exhibit more deeply seated structural modifications. The Lepidoptera are all vegetable-feeders in
their larva-state, and suckers of juices or other liquids
in their perfect form. In their most widely separated
groups they differ but little from a common type,
and offer comparatively unimportant modifications of
structure or of habits. The Coleoptera, the Diptera,
or the Hymeioptera, on the other hand, present far
greater and more essential variations. In either of
these orders we have both vegetable and animalfeeders, aquatic, and terrestrial, and parasitic groups.
Whole families are devoted to special departments in
the economy of nature. Seeds, fruits, bones, carcases, excrement, bark, have each their special and