CHAP. V 



COLEOPTERA BEETLES 



I8 5 



of the hard parts of the skeleton is of importance, as the classi- 

 fication of this enormous number of species is entirely based 

 thereon ; it will be readily understood from the accompanying 

 diagram (Fig. 83). The general proportions of the chief parts 

 of the body call for a few remarks. The prothorax is remarkably 

 free, and is therefore capable of a much greater amount of move- 

 ment independent of the after-body than it is in other Insects. 

 The mesothorax is, on the other hand, much reduced ; its chief 

 function in the higher forms is to support the elytra, and to 



FIG. 83. Under-surface of a beetle, 

 Harpalus caliginosus ; legs and 

 antenna of one side, and some parts 

 of the mouth removed. A, an- 

 tenna ; B, mandible ; C, labrum ; 

 D, ligula ; E, paraglossa ; F, labial 

 palp ; G, inner lobe of maxilla ; 

 H, outer lobe (palpiform) of 

 maxilla ; I, maxillary palp ; K, 

 mentum ; L, gena ; M, gula ; N, 

 buccal fissure ; V, plates of ven- 

 tral segments. 1, Prosternum ; 

 2, prosternal episternum ; 3, pro- 

 sternal epimeron ; 4, anterior and 

 middle coxal cavities ; 5, inflexed 

 side of pronotum ; 6, mesosternum ; 

 7, mesosternal episternum ; 8, 

 mesosternal epimerou ; 9, meta- 

 sternum ; 10, posterior division of 

 metasternum or ante-coxal piece ; 

 11, metasternal episternum ; 12, 

 metasternal epimeron ; 13, epi- 

 pleuron or inflexed margin of ely- 

 tron ; 14, ventral or ambulatory 

 setae ; 15, trochanter ; 16, pos- 

 terior coxa ; 17, femur ; 18, tibia ; 

 19, tarsus. (Modified from Le- 

 conte and Horn.) 



help to keep them together by means of its scutellum. The 

 metathorax, on the contrary, is largely developed, except in the 

 rather numerous forms that are entirely deprived of powers of 

 night. The composition of the abdomen has been a subject of 

 great difference of opinion. Its upper surface is usually entirely 

 covered by the elytra ; the parts visible on the lower surface are 

 called ventral segments, and are usually five in number. Although 

 these five plates may constitute all that is superficially visible of 

 the abdomen, yet if the elytra are taken off it is found that a larger 

 number of segments usually seven or eight are visible on 

 the dorsum. This seeming discrepancy of number between the 



