6 NATURAL HISTORY OF AQUATIC INSECTS 



proof that Insects were primarily air-breathing 

 animals, but the distribution throughout the different 

 orders and families of the species which breathe gas- 

 eous air and of those which breathe only air dissolved 

 in water, leaves no doubt that the last-named species 

 are those which deviate from the general and primitive 

 rule. I think that every entomologist would agree 

 that the Insects which exhibit the most generalised 

 and presumably the most primitive structure are 

 terrestrial rather than aquatic. 



Insects are just the sort of animals that might have 

 been supposed likely to change from one medium to 

 another with great ease and advantage. They are 

 active, hardy and ingenious. The plan of their bodily 

 structure has lent itself to a multitude of special 

 adaptations of other kinds. Notice the various shapes 

 of Insects. We find among Beetles, for instance, some 

 so round and fat that they can hardly creep, some 

 long-legged and nimble, one as flat as a wafer for 

 convenience of creeping under the adherent bark of 

 fallen trees, some with long wings, others with short 

 wings, others with no wings at all. Then among 

 caterpillars what a range of shapes ! They may be 

 long and narrow, or egg-shaped, hard or soft, with 

 many feet or with none, hairy or smooth, and in 

 special cases with the oddest horns, warts, brushes, 

 tentacles and hooks. Notice too, the extraordinary 

 variety in their food. Insects can be found which live 

 upon wood, upon earth and the things contained in 

 earth, upon fungi, upon decaying seaweed, upon paper, 

 upon fur and wool, upon leather, upon argol (crude 

 potassium tartrate), in addition to the animal and 



