14 COLEOPTERA OF INDIANA. 



THE THOKAX AND ITS APPENDAGES. 



The second division or middle region of the body of an insect is 

 called the thorax and consists of three rings or segments, known 

 respectively as the proilwrax, mesothorax and metathorax. Within 

 these rings are located the muscles moving the legs and wings, as 

 well as some of the digestive organs, while attached to their upper 

 surface are the wings and to the lower one the three pairs of legs. 



The Prothorax. In the beetles the prothorax or front ring is 

 separated from the other two and is usually freely movable. It con- 

 sists of a dorsal or upper surface of but one piece and a ventral or 

 lower part of five pieces. The upper part is often called the pro- 

 notum, but in this paper it is termed the thorax, since it is the 

 median one of the three body parts visible from above. In the dif- 

 ferent species of beetles it varies greatly in size and sculpture, and 

 these variations are very extensively used in classification. 



The dorsal surface is called the disk, and this is usually sep- 

 arated from the inflexed portion or flanks by a sharp edge or acute 

 margin. The relative width and length of the disk, the form of its 

 front and hind angles, the presence or absence of a median im- 

 pressed line and of impressions or fovea?, the form, size arid density 

 of the punctures when present, are but a few of the many points 

 pertaining to the thorax which are used in the description of a 

 beetle. 



The Prosternum. The central part of the under surface of the 

 prothorax is the prosternum. It is situated in front of the coxa; 

 of the first pair of legs and often has a process or spine which ex- 

 tends backward between these coxae, its tip sometimes, as in the 

 Elateridae, fitting into a notch or groove in the mesosternum. Tl-.e 

 prosteruum is sometimes prolonged in front to form a prosit,, in' 

 lobe, which more or less conceals the mouth when the head is m >-^ 

 pose. On either side of the prosternum and between its side in-a 1 - 

 gin and the flank of the pronotum (or thorax), are one or two 

 "side-pieces." When both pieces are present the front one is called 

 the episternum (plural episterna}, and the hind one the epimeron 

 (plural epimera) . Most frequently the sutures or seams between 

 these pieces and also between them and the flank of the pronotum 

 are wanting, so that the disk and flanks of thorax form one un- 

 broken piece as far as the side of the prosternum. The sutures 

 separating the prosternum and the side-pieces are more often pres- 

 ent and are known as the prosternal sutures. 



The cavities in which the first pair of legs are inserted are called 



