INSECTS, Fossm. Of all animals the insects, with their a;rial habits of life, would seem at first. thought to be the least liable to entombment and preservation in a fossil state. They are, however, found in great abundance in several localities where the nature of the deposition was particularly favorable to their fossilization. These deposits are nearly all of fresh-water (lacustrine or marsh) or of estuarine origin, though some few are purely marine. Asa rule the imbedding materials are finely grained shales or limestone concretions in shales, or fossil gums and amber; the anther has furnished by far the most perfect fossil insects known. The shale beds of the Oligocene Tertiary at Florissant, Colo., are also noted for the abundance and per fection of their insect contents. Other noted re positories of fossil insects are the Carboniferous coal-measure beds of Commentry, France, de scribed by Brongniart ; the Liassic beds of Scham belen. Switzerland. of Dohbertin. Germany, and of Gloucestershire. England; and the .Turassie lithographic limestone of Bavaria. The Ter tiary localities, from which great numbers of insect remains have been derived. are the Baltic provinces of Germany and Russia, where they occur in amber; the shales of Aix, France, Floris sant and the White River District of Colorado, and ()ening, Radoboj. and Parshberg. The wings seem to be preserved as fossils far more often than other parts of the insect body, and in many formations these are the only parts found.
The known fossil insects do not present any great points of difference from those now living. Those found in the Mesozoic and Tertiary rocks can be readily placed in modern families; but all Paleozoic insects show a certain general resem blance, with here and there points of relation ship to the orders of modern insects. These or ders did not become fully differentiated until Triassic time, although ancestral forms are easily distinguishable among the earlier members of the class. The Paleozoic insects have on this ac count, been grouped under the name of Pa•uo dietyoptera, a synthetic• group, and have been distributed, according to their resemblances to modern forms, among several orders—the Or thopteroiden, Neuropteroidea, Ilemipteroiden, etc., which are directly ancestral to the Post Paleozoic and modern orders of Orthoptera, Neu roptera, Ilemiptera, etc. The Paleozoic insects are of more primitive type, as illustrated chiefly in the wing-structure. than are the Mesozoic in seets. As a rule their front wings are mem branous—i.e. they had not yet evolved hardened front wings, such DS the ylytra and te,gmina, that serve as protective coverings for the inure deli cate hind wings of modern insects. Some of the early insects were of gigantic size, compared with their living deseendants—Meganeura, an ancestral dragon-fly found in the Carboniferous. of Cominentry, France, had a body 10.5 inches long, and its wings spread over inches. An other point of interest is that the Paleozoic in sect fauna was made up almost entirely of cock roaches. These must have swarmed in the woods and swamps of the Carboniferous and Triassic periods, for their remains are found in abundance in the shales and sandstones associated with the coal deposits of those ages.
The earliest insects are of very fragmentary nature. The oldest known is supposed to be an ancestor of the bedbugs (Protocimex) found in the Ordovician rocks of Sweden and represented by a single wing. In the Silurian the cockroaches appeared, and they were the predominating types in the Devonian and Carboniferous. The Car boniferous fauna consists principally of Orthop tern and Neuroptera, and of forms intermediate between these two orders, and also of extinct types intermediate between the Orthoptera and the Ilemiptera. and it is interesting because of its large number of generalized or synthetic types. In the Triassic the beetles appear suddenly with their characteristic hardened front wings fully developed. This difference in the character of the front and hind wings is fully marked for the first time in all Triassic. insects, and it has be come more strongly marked since that period. In the Liassic epoch of the Jurassic period in sects were abundant, as might be expected from the general extension of terrestrial eonditinns during that period. Beetles abound. and as they represent many families still living. they have been used to determine the conditions of life and climate during that period. Leaf and fungus eating beetles and dung-beetles are known. The earliest ants; first well-marked bugs, allies of the squash-bug; the first flies. bees, and perhaps also the earliest moths, are found in this epoch. The Cretaceous insect fauna is small. but that of the succeeding Tertiary, beginning with the Eoecne, is almost as well differentiated as that of the present day, for many of the genera are still members of the living insect fauna. In all about 3000 species of fossil insects are known, and these are distributed among the geological eras as follows: About 10 per cent. are l'aleo zoie, 15 per cent. Mesozoic, and 75 per cent. have been described from the Tertiary formations.
BIBLIOGRAPHY. Von Zittel and Eastman, TextBibliography. Von Zittel and Eastman, Text- book of Paleontology, vol. i. (London and New York. 1900) ; Zittel and Barrois, Traite do paljontologie, part i., vol. ii. (Paris, Munich, and Leipzig, 1887) ; Scudder, "Systematic Re view of Our Present Knowledge of Fossil In sects," in Bulletin of the United States Geolog ical Surrey No. 37 (Washington, 1SS6) ; also "The Tertiary Lake Basin at Florissant, Colo rado," in Twelfth Annual Report of the Geologic al and Geographical Survey of the Territories, Hayden in Charge, for 1S7S (Washington, 1883) ; Fossil Insects of North America. (2 vols., New York, 1890) ; and other papers by same author in Bulletins of the United States Geological Surveg, Nos. 69, 71, 93, 101, and 124 (Washing ton, 1890-95), in Monographs of United States Geological Survey, vols. x.xi. and xl. (Washing ton, 1893-1900), and in Annual Report of the United States Geological Survey, vol. sill., part ii. (Washington, 1893). For descriptions and fine figures of the interesting insect fauna of Commentry, France, see Brongniart, Recherches pour servir it l'histoire des insectes fossilcs des temps primaircs (2 vols., Saint Etienne, 1893). See also articles on orders of insects.