158 ENTOMOLOGY 



Scarabaeidae, Chrysomelidae, Coccinellidae, etc.), dragon flies, moths, 

 butterflies (Anosia, Pieris, etc.) and various Hemiptera, Hymenoptera 

 and Diptera. A large proportion of the insects were aquatic forms, such 

 as Hydrophilus, Cybister, Zaitha, and a species of caddis fly; these had 

 doubtless been carried out by freshets, while the butterflies and dragon 

 flies had been borne out by a strong wind from the northwest, after which 

 all were driven back to the coast by a northeast wind. While some of 

 these insects survived, notably Coccinellidae, Trichoptera, Asilidae, 

 Acridiidae and Gryllidae, nearly all the rest were dead or dying, in- 

 cluding the dragon flies, flies, bumble bees and wasps. Foraging Cara- 

 bidae were observed in large numbers, also scavengers of the families 

 Staphylinidae, Silphidae and Dermestidae. 



On the seashore and on the shores of the Great Lakes, the salient 

 features of insect life are essentially the same. Similar species occur in 

 the two places with similar biological relations, on account of the general 

 similarity of environment. 



Origin of the Aquatic Habit. The theory that terrestrial insects 

 have arisen from aquatic species is no longer tenable, for the evidence 

 shows that the terrestrial type is the more primitive. Aquatic insects 

 still retain the terrestrial type of organization, which remains unob- 

 scured by the temporary and comparatively slight adaptations for an 

 aquatic life. Thus, the development of tracheal gills has involved no 

 important modification of the fundamental plan of tracheal respiration. 

 It is significant, moreover, that the most generalized, or most primitive, 

 insects Thysanura are without exception terrestrial. Aquatic in- 

 sects do not constitute a phylogenetic unit, but represent various orders, 

 which are for the most part undoubtedly terrestrial, notwithstanding the 

 fact that a few of these orders (Plecoptera, Ephemerida,-Odonata, Tri- 

 choptera) are now wholly aquatic in habit. Adaptations for an aquatic 

 existence have arisen independently and often in the most diverse 

 orders of insects. 



