86 INSECTS CHAP. 



are called collectively Entomology. Although entomology is 

 only a department of the great science of zoology, yet it is in 

 practice a very distinct one : owing to its vast extent few of 

 those who work at other branches of zoology also occupy them- 

 selves with entomology, while entomologists usually confine 

 themselves to work in the vast field thus abandoned to them. 



Before passing to the consideration of the natural history and 

 structure of the members of the various Orders of Insects we will 

 give a verbal diagrammatic sketch,if we may use such an expression, 

 with a view to explaining the various terms that are ordinarily 

 used. We shall make it as brief as possible, taking in succession 

 (1) the external structure, (2) internal structure, (3) development of 

 the individual, (4) classification. 



In the course of this introductory sketch we shall find it 

 necessary to mention the names of some of the Orders of Insects 

 that will only be explained or defined in subsequent pages. AVc 

 may therefore here state that the term " Orthoptera " includes 

 grasshoppers, locusts, earwigs, cockroaches ; " Neuroptera " com- 

 prises dragon-flies, May-flies, lacewings, stone-flies and caddis-flies ; 

 to the " Hymenoptera " belong bees, wasps, ants, sawflies, and a 

 host of little creatures scarcely noticed by the ordinary observer : 

 " Coleoptera " are beetles ; " Lepidoptera," butterflies and moths ; 

 " Diptera," house-flies, blue -bottles, daddy-longlegs, and such ; 

 " Hemiptera " or " Ehynchota " are bugs, greenfly, etc. 



Class Insecta : or Insecta Hexapoda. 



Definition. Insects are small animals, having the body divided 

 into three regions placed in longitudinal succession head, thorax, 

 and abdomen : they take in air by means of tracheae, a system of 

 tubes distributed throughout the body, and opening externally by 

 means of orifices placed at the sides of the body. They have six 

 legs, and a pair of antennae ; these latter are placed on the head, 

 while the legs are attached to the thorax, or second of the three great 

 body divisions ; the abdomen has no true legs, but not infrequently 

 has terminal appendages and, on the under surface, protuberances 

 which serve as feet. Very frequently there are two pairs of 

 wings, sometimes only one pair, in other cases none : the wings 

 are always placed on the thorax. Insects are transversely seg- 

 mented that is to say, the body has the form of a succession of 



