INTRODUCTION 7 



vegetable products which are the ordinary food of the 

 higher animals. 



Equally remarkable is the facility with which Insects 

 adapt themselves to various conditions. The most 

 primitive Insects are terrestrial, running about on the 

 surface of the earth to seek their food. But many 

 have learnt to burrow into the earth, and this in a 

 great variety of ways. A large proportion have 

 learnt to fly. Some run their galleries in the wood of 

 trees ; others cat out slender mines in the thickness 

 of a leaf; others live in the bodies of dead animals ; 

 and there are not a few which burrow in the bodies 

 of living animals — a painful example of the cruelty of 

 Nature ! The adaptations of Insects to aquatic life, 

 varied and ingenious as we shall find them to be, are 

 only fresh examples of the versatility which character- 

 ises the whole class. 



Even if we confine our attention to the Insects 

 which pass part or the whole of their lives in water, 

 we shall find a great diversity in their habitats. Still 

 water abounding in vegetation is suitable to many ; 

 others like running water, and some few prefer torrents 

 or cascades, though in this case they are seldom 

 exposed to the full force of the current. The most 

 rapid parts of an English mountain brook will, how- 

 ever, often be found to harbour certain kinds of 

 Caddis-worm and the larvae of Simulium. Water 

 loaded with dead organic matter is congenial to other 

 Insects, and the larva of Eristalis tenax prefers water 

 which is putrid and stinking. Salt water is selected by 

 others. The sea nourishes a considerable number, 

 and brine-pits, notwithstanding the bitterness and 



