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Page:Popular Science Monthly Volume 70.djvu/65

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61
FOSSIL INSECTS

have to provide themselves with much larger nets should the thousands of past generations of insects celebrate a joyous resurrection, for the size of these Jurassic representatives was from four to five times that of many forms now existing in the Danube region.

But these fertile years were apparently preceded by others more barren. At least this impression is gained when we contemplate the swarms of insects that lie buried in a stage still lower—the Lias, or black Jura. The discovery of some rich localities in Switzerland, in Mecklenburg and in England, for instance, have yielded almost absolutely dwarf species. On the average, these forms were even smaller than those inhabiting the same regions to-day; truly starved species. In fact, at that time there were as yet no butterflies, few Hymenoptera, and no other striking insects. The beetles and gnats found were small and insignificant. On the other hand, caddice-flies and scorpion-flies were abundantly.represented, the latter of which now play only a limited part. There were also dragon-flies of moderate dimensions, bugs and small cicadas similar to our frog-hoppers; grasshoppers and locusts, and the ever-present cockroach as well.

From the long Triassic period that stored up a large part of the material from which the imposing dolomite towers were subsequently formed, we as yet unfortunately know only some insignificant beetles and Neuroptera. Hence, we can turn at once to that very ancient period called the Paleozoic. On important but purely material grounds, this epoch stands very close to mankind in general, since it includes the most valuable coal deposits, the mining of which has materially aided our present studies. In and near the coal in many places in Europe and North America has been found a great number of impressions of insects whose investigation furnishes us with an entirely new world of forms.

Although in the upper beds of this period no more beetles and Neuroptera are found, yet caddice-flies and scorpion-flies, gnats and locusts, too, are wanting. So much the more do the cockroaches increase! May-flies and stone-flies were already represented, and Hemiptera as well, but of a form that it is not known whether they should be pronounced cicadas or bugs.

In addition we also find insects that it may not be possible to arrange in the established classification of living forms, although affinities with the latter are undoubtedly to be recognized. The deeper we descend into the coal period, these forms more and more increase in number, while modern types gradually become less and less frequent. It may therefore be concluded that in the Carboniferous forms the direct ancestors of many of the insect groups previously mentioned are to be sought, and hence corresponding names have been chosen for them: as Protodonata, the ancestors of the Odonata, or libellids;