It goes without saying that such delicate frames as
those of the earlier insects had very little chance of being
preserved in the rocks until the special conditions of the
forest-age set in. We are, therefore, quite prepared to hear that
the geologist cannot give us the slenderest information. He finds
the wing of what he calls "the primitive bug" (Protocimex), an
Hemipterous insect, in the later Ordovician, and the wing of a
"primitive cockroach" (Palaeoblattina) in the Silurian. From
these we can merely conclude that insects were already numerous
and varied. But we have already, in similar difficulties,
received assistance from the science of zoology, and we now
obtain from that science a most important clue to the evolution
of the insect.
In South America, South Africa, and Australasia, which were at
one time connected by a great southern continent, we find a
little caterpillar-like creature which the zoologist regards with
profound interest. It is so curious that he has been obliged to
create a special class for it alone--a distinction which will be
appreciated when I mention that the neighbouring class of the
insects contains more than a quarter of a million living species.
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