192 ENTOMOLOGY 



eluding the dragon flies, flies, bumble bees and wasps. Fora- 

 ging Carabidse were observed in large numbers, also scaven- 

 gers of the families Staphylinidse, Silphidge and Dermestidse. 



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

 salient features of insect life are essentially the same. Sim- 

 ilar 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 unobscured 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 terres- 

 trial. Aquatic insects do not constitute a phylogenetic unit, 

 but represent various orders, which are for the most part un- 

 doubtedly terrestrial, notwithstanding the fact that a few of 

 these orders (Plecoptera, Ephemerida, Odonata, Trichoptera) 

 are now wholly aquatic in habit. Adaptations for an aquatic 

 existence have arisen independently and often, in the most 

 diverse orders of insects. 



