12 THE CLASS OF INSECTS. 



such as the PotystoecJiotes (Fig-. 13 a), the pne- 

 scutiun is largo, well developed, triangular, and wedged in 

 between the two halves of the scutum. The little 

 piece succeeding the scutellum, i. < j . the postscu- 

 tellum, is still smaller, and rarely used in descrip- 

 tive entomology. Thus tar \ve have spoken of the 

 middle, or mesothoracic, ring, where these four 

 pieces are most equally developed. In the iirst, " 

 or prothoracic, ring, one part, most probably the 

 scutum, is well developed, while the others are 

 aborted, and it is next to impossible to trace them 

 in most insects. The prothorax in the higher in- Fi ~- 1:i - 

 sects, such as the Hymenoptera, Lepidoptera, and Diptera is 

 very small, and often intimately soldered to the succeeding or 

 mesothoracic ring. In the lower insects, however, such as the 

 Coleoptera, the bugs (Ilemiptera), grasshoppers and their 

 allies (Orthoptera). and the Xeuroptera, the large broad pro- 

 thorax consists almost entirely of this single piece, and most 

 writers speak of this part under the name of "thorax," since 

 the two posterior segments are concealed by the wings when 

 the animal is at rest. The metathorax is usually very broad 

 and short. Here we see the scutum split asunder, with the 

 pra'sciitum and scutellum wedged in between, while the post- 

 scutellum is aborted. 



On the side are two pieces, the upper (epimernm) placed 

 just beneath the tergum, which is the collective name for the 

 four tergal, or dorsal, pieces enumerated above. In front of 

 the epimerum and resting upon the sternum, as its name im- 

 plies, is the ejiixfcnmiii. These two parts (pleurites) compose 

 the flanks of the elemental ring. To them the legs are articu- 

 lated. Between the two episterna is situated the breast-piece 

 (sternum), which shows a tendency to grow smaller as we 

 ascend from the Neuroptera to the Bees. 



In those insects provided with wings, the epimera are also 

 sul (divided. The smaller pieces, hinging upon each other, as 

 it were, give play to the very numerous muscles of flight 



l-'iu. 13. A terjral view of thorax of Heputliis(Sthenojiis'); 1, prothorax; '2, meso- 

 ihorux; 3, iiu'tathor.'ix. The prothorax is very small compared with that of l'<>ly- 

 vtifi-litites (13 tt, 1), whirr it is nearly as long as broad. Orif/inaf. 



