EXTERNAL ANATOMY OF INSECTS. 581 



usually three pedigerous segments, there is no distinction 

 of dorsolum, scutellum, &c. In the Scolopendridtz and 

 Scutigera amongst the Myriapods, according to the acute 

 observations of M. Savigny a , — on which, however, some 

 doubt at present rests, — there is a remarkable formation, 

 the whole thorax being represented by the single plate 

 that follows the head, to the under-side of which are at- 

 tached the first and second pair of palpi or pedipalpi, 

 and the first pair of legs, representing the three pairs of 

 legs of hexapods. In the Iididce the three segments that 

 follow the head, each bear a single pair of legs, while all 

 the rest bear a double one : from whence it should seem 

 to follow, that these segments and their legs represent 

 the trunk and legs of Hexapods. In the Octopod Aptera 

 and the Arachnida the trunk consists of a single piece, 

 not separated from the head, and sometimes not distinct 

 from the abdomen. 



V. Internal processes b . Perhaps you will think that 

 this head would be better considered when I treat of the 

 Internal Anatomy of Insects; but as the parts included 

 under it are really processes of the external integument 

 of the trunk, it seemed to me best to treat of them under 

 that head. They are of two descriptions ; processes of 

 the thorax or upper part of the trunk, and processes of 

 the breast or its under part. 



i. Processes of the thorax . These are the jjhragma, 

 prophragma, mesophragma, and metaphragma. The first 

 belongs to the prothorax, the second to the mesothorax, 



a Mem. sur les Anim. sans Fertebr. 45 — . Hor. Entomolog. 411 — . 

 b Plate VIII. Fig. 3. x . IX. Fig. 2. s. and XXII. Fig. 5— 

 14. c Plate XXII. Fig. 8— 11. 



