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 in the Oolite; while ants, representing the highly specialised Hymenoptera, have occurred in the Purbeck and Lias.

This remarkable identity of the families of very ancient with those of existing insects is quite comparable with the apparently sudden appearance of existing genera of trees in the Cretaceous epoch. In both cases we feel certain that we must go very much farther back in order to find the ancestral forms from which they were developed, and that at any moment some fresh discovery may revolutionise our ideas as to the antiquity of certain groups. Such a discovery was made while Mr. Scudder's work was passing through the press. Up to that date all the existing orders of true insects appeared to have originated in the Trias, the alleged moth and beetle of the Coal formation 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)