DISTRIBUTION 389 
species, the continuity between Paleozoic and recent cock- 
roaches 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 Planor- 
bis. In the Triassic period occur the first fossils that can be 
Fic. 299. 
roo NT, OTT 
fer RI | BEL 
Ue 
“el ae ar ; 
ene 
Eugereon béckingi. Three quarters natural size.—After Dourn. 
referred indisputably to Coleoptera and Hymenoptera, the lat- 
ter 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 Lepidoptera occur; Diptera appear for the first time, 
and Odonata are represented by many well-preserved speci- 
mens, 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 
Psocidze, many Diptera, and ants in abundance. Of 844 spe- 
