n having been
incorrectly determined. But now, undoubted remains of beetles have been
found in the Coal measures of Silesia, thus supporting the
interpretation of the borings in carboniferous trees as having been made
by insects of this order, and carrying back this highly specialised form
of insect life well into Palaeozoic times. Such a discovery renders all
speculation as to the origin of true insects premature, because we may
feel sure that all the other orders of insects, except perhaps
hymenoptera and lepidoptera, were contemporaneous with the highly
specialised beetles.

The less highly organised terrestrial arthropoda--the Arachnida and
Myriapoda--are, as might be expected, much more ancient. A fossil spider
has been found in the Carboniferous, and scorpions in the Upper Silurian
rocks of Scotland, Sweden, and the United States. Myriapoda have been
found abundantly in the Carboniferous and Devonian formations; but all
are of extinct orders, exhibiting a more generalised structure than
living forms.

Much more extraordinary, however, is the presence in the Palaeozoic
formations of ancestral forms of true insects, termed by Mr. Scudder
Palaeodictyoptera. They consist of generalised cockroaches and
walking-stick insects (Orthopteroidea); ancient mayflies and allied
forms, of which there are six families and more than thirty genera
(Neuropteroidea); three genera of Hemipteroidea resembling various
Homoptera and Hemiptera, mostly from the Carboniferous formation, a few
from the Devonian, and one ancestral cockroach (Palaeoblattina) from
the Middle Silurian sandstone of France. If this occurrence of a true
hexapod insect from the Middle Silurian be really established, taken in
connection with the well-defined Coleoptera from the Carboniferous, the
origin of the entire group of terrestrial arthropoda is necessarily
thrown back into the Cambrian epoch, if not earlier. And this cannot be
considered improbable in view of the highly differentiated land
plants--ferns, equisetums, and lycopods--in the Middle or Lower
Silurian, and even a conifer (Cordaites Robbii) in the Upper Silurian;
while the beds of graphite in the Laurentian were probably formed from
terrestrial vegetation.

On the whole, then, we may affirm that, although the geological record
of the insect life of the earth is exceptionally imperfect, it yet
decidedly supports the evolution hypothesis. The most specialised order,
Lepidoptera, is the most recent,