DISTRIBUTION 345 



with hemipterous mouth parts associated with filiform antennae and 

 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 CEningen, 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 OEningenby Scudder, Hymenoptera 

 constitute 4.0 per cent, of the specimens, owing chiefly to the predomi- 

 nance 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, more than thirty species of Aphididae, and 

 more than 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. Nu- 

 merous masses of eggs occur, undoubtedly sialid and closely like those of 



