INTRODUCTION. 



11 



composed of three distinct segments — viz., prothorax, mesothorax, and 

 metathorax, each of which 

 may be built up of several 

 pieces. These segments vary 

 in proportion in different in- 

 sects, and they also vary in 

 the respective stages of the 

 life of an individual insect. 

 The thorax and its compon- 

 ent parts are of considerable 

 importance in the discrimin- 

 ation of species, as, for in- 

 stance, in the Hymenoptera. 



The third region is known 

 as the abdomen, and is very 

 variable in form, according 

 to order and genus. It is 

 generally composed of nine 

 segments, and bears the 

 organs of reproduction. 



The wings, as appendages, 

 are very important points in the discrimination of genera and species 

 In fact, some writers use the wings 

 as a basis of classification. So far 

 as forest entomology is concerned, 

 it is highly essential to make a 

 detailed study of the structure of 

 the wings of saw-flies, gall-flies, 

 Aphididae, and Diptera. 



The structure of the leg is also 

 of importance in the classification of 

 species. If we separate a leg from 

 the body of the insect and examine 

 it, from the connection with the 

 body to the tip, we shall find it is 

 composed of several parts. The 

 leg is attached to the body by a 

 joint called the coxa ; next to this is a very small portion known as 

 the trochanter, which serves as a sort of joint or hinge connecting the 



Fig. 12. 



Tiipical forms of antenna;. (From drawings 

 by Mr G. A. Dunlop.) 



Coxa. 



'frocbaofer. 



Fcnjur. 



"Tibia. 



"tarsus. 



—Typical form of leg. (From draw- 

 ing by Mr G. A. Dunlop.) 



