ating plants, the
climbers, the parasites, the sensitive plants, the water-storing plants
in dry regions, and so on--we must turn to the consideration of the
insects themselves. We have already studied the evolution of the insect
in general, and seen its earlier forms. The Tertiary Era not only
witnessed a great deployment of the insects, but was singularly rich in
means of preserving them. The "fly in amber" has ceased to be a puzzle
even to the inexpert. Amber is the resin that exuded from pine-like
trees, especially in the Baltic region, in the Eocene and Oligocene
periods. Insects stuck in the resin, and were buried under fresh layers
of it, and we find them embalmed in it as we pick up the resin on the
shores of the Baltic to-day. The Tertiary lakes were also important
cemeteries of insects. A great bed at Florissart, in Colorado, is
described by one of the American experts who examined it as "a Tertiary
Pompeii." It has yielded specimens of about a thousand species of
Tertiary insects. Near the large ancient lake, of which it marks the
site, was a volcano, and the fine ash yielded from the cone seems to
have buried myriads of insects in the water. At Oeningen a similar
lake-deposit has, although only a few feet thick, yielded 900 species of
insects.

Yet these rich and numerous finds throw little light on the evolution of
the insect, except in the general sense that they show species and even
genera quite different from those of to-day. No new families of insects
have appeared since the Eocene, and the ancient types had by that time
disappeared. Since the Eocene, however, the species have been almost
entirely changed, so that the insect record, from its commencement
in the Primary Era, has the stamp of evolution on every page of it.
Unfortunately, insects, especially the higher and later insects,
are such frail structures that they are only preserved in very rare
conditions. The most important event of the insect-world in the Tertiary
is the arrival of the butterflies, which then appear for the first time.
We may assume that they spread with great rapidity and abundance in
the rich floral world of the mid-Jurassic. More than 13,000 species of
Lepidoptera are known to-day, and there are probably twice that number
yet to be classified by the entomologist. But so far the Tertiary
deposits have yielded only the fragmentary remains of about twenty
individual butterflies.

The evolutionary study of the insects is, the