INSECTS. 251 



are setae, like as in the beak, which form the sucker (haustellum). 

 A triangular upper lip covers the basal piece of the beak in Hemi- 

 ptera, as it does that of the snout in Diptera. 



To the head succeeds the trunk or thorax. This part consists 

 of three pieces, of which each bears a pair of feet. The first ring is 

 named Prothorax, the second Mesothorax, the third MetatJwrax. In 

 four-winged Insects the anterior wings are placed on the middle 

 piece, the posterior wings on the hinder piece. The wings of Di- 

 ptera are placed on the mesothorax. The inferior surface of the 

 trunk is called breast (pectus), on which there is sometimes fixed a 

 pointed elongated appendage, the breast-bone (sternum). The 

 shield (scutellum) is a part found on the upper part of the thorax 

 behind (at the mesothorax) stretching between the wings 1 . 



The feet are attached on the inferior surface of the body : in the 

 hexapod Insects every ring of the thorax carries a pair. Between 

 the sternum and epimeron is an articular cavity (acetabulum) . The 

 first joint is termed hip (coxa, condylus) ; sometimes there is a small 

 and very moveable piece between the epimeron and coxa (trochan- 

 terium, trochantin AUDOUIN), but it is usually wanting or has coa- 

 lesced with the coxa. The second joint is termed Trochanter, it is 

 very small and mostly annular. Then comes the thigh (femur), the 

 stoutest, and often also the longest joint of the leg. To it succeeds 

 the shank (tibia) more slender, and in general flattened laterally. 

 Last is the foot (tarsus), consisting of many joints placed in a line 

 like the small bones of our fingers. The number of these joints is 

 different in different families; occasionally, in certain coleopterous 



1 The upper surface of the thorax (dorsum of AUDOUIN) may be named notum, the 

 under surface sternum, and just as the entire thorax is divided into three rings, so also 

 a pronotum and prosternum, mesonotum and mesosternum, metanotum and metasternum 

 may be distinguished. Moreover, each ring of the thorax consists of definite special parts, 

 which, however, are not distinctly seen in every ring, whilst some coalesce with others, 

 or by the greater development of others are suppressed ; these parts are a sternum on 

 the under surface, on either side an episternum as a chief part, and behind this an 

 epimeron; and, finally, on the upper four pieces placed behind each other, to which 

 AUDOUIN gives the names of prcescutum, scutum, scutellum and post- scutellum; thus 

 there are properly three scuteUa, but what is usually named scutellum is a part of the 

 mesonotum; at the sides of the scutum the wings are attached. Comp. on this interesting 

 subject AUDOUIN, Recherches anatomiques sur le thorax des Animaux articules, Ann. des 

 Sc. nat. i. 1824, pp. 97 135, 416 432, W. S. MAC-LEAY, Comp. Anat. of thorax in 

 winged Insects. Zoolog. Journal, No. 18, or Ann. des Sc. nat. xxv. 1832, pp. 95 151, 

 with remarks by AUDOUIN and NEWPORT, TODD'S Cyclopcedia,, II. pp. 911 924. 



