^22 ENTOMOLOGY 



orthopteroid wings. The earliest unquestionable traces of insects with 

 an indirect metamorphosis are found in the Permian of Bohemia, in 

 the shape of caddis-worm cases. 



Triassic. Triassic cockroaches present interesting stages in the 

 evolution of their family. Through these Mesozoic species the con- 

 tinuity between Palaeozoic and recent cockroaches is clearly established 

 which can be said of no other insects; and in fact of no other animals, 

 the only comparable cases being those of the horse and the molluscan 

 genus Planorbis. In the Triassic period occur the first fossils that can 

 be referred indisputably to Coleoptera and Hymenoptera, the latter order 

 being represented first, as it happens, by some of its most specialized 

 members, namely ants. 



Jurassic. At length, in the Jurassic, all the large orders except Lep- 

 idoptera occur; Diptera appear for the first time, and Odonata are rep- 

 resented by many well-preserved specimens, while the Liassic Coleoptera 

 studied by Heer number over one hundred species. The Cretaceous 

 has yielded but few insects, as might be expected. 



Tertiary. In the rich Tertiary deposits all orders of insects occur. 

 Baltic amber has yielded Collembola, some remarkable Psocidae, many 

 Diptera, and ants in abundance. Of 844 species taken from the noted 

 Miocene beds of (Eningen, nearly one half were Coleoptera, followed by 

 neuropteroid forms (seventeen per cent.) and Hymenoptera (fourteen 

 ' per cent.) ; ants were twice as numerous in species as they are at present 

 in Europe. Almost half the known species of fossil insects have been 

 described from the Miocene of Europe. To the Miocene belongs the 

 indusial limestone of Auvergne, France, where extensive beds in some 

 places two or three meters deep consist for the most part of the cal- 

 cified larval cases of caddis flies. 



At Florissant, as contrasted with (Eningen by Scudder, Hymenoptera 

 constitute 40 per cent, of the specimens, owing chiefly to the predominance 

 of ants; Diptera follow with 30 per cent, and then Coleoptera with 13 

 per cent. Modern families are represented in great profusion. The 

 material from Florissant and neighboring localities includes a Lepisma, 

 fifteen species of Psocidae, over thirty species of Aphididae, and over one 

 hundred species of Elateridae, while the Rhynchophora number 193 

 species as against 150 species from the Tertiary of Europe, Tipulidae 

 are abundant and exquisitely preserved, while Bibionidae, as compared 

 with their present numbers, are surprisingly common. Numerous masses 

 of eggs occur, undoubtedly sialid and closely like those of Corydalis. 

 Sialid characters, indeed, appear in the oldest fossils known, and are 



