STRUCTURE OF INSECTS. 323 



narrow filament, or neck ; so that the articulation 

 is effected by ligament alone. Occasionally it 

 is placed at the end of a long pedicle, which 

 removes it to a considerable distance from the 

 trunk. In the Hymcnoptera and Diptera, the 

 head moves upon a pivot, so as to admit of its 

 being turned completely round. 



The trunk, or Thorax, is composed, as shown 

 in the figure, of three segments, termed respect- 

 ively the Prothorax (x) ; the Mesothorax (Y) ; 

 and the Metathorax (z).* The first of these, the 

 prothorax, carries the first pair of legs ; the 

 second, or mesothorax, gives origin to the 

 second pair of legs, and also to the first pair of 

 wings, or to the Elytra (E), as in the example 

 before us ; and the third, or metathorax, sup- 

 ports the third pair of legs, and the second pair of 

 wings (w). These two last segments are closely 

 united together, but the original distinction 

 into two portions is marked by a transverse line. 

 Each of these three segments is divisible into an 

 upper, a lower, and two lateral portions, which 



* In these denominations I have followed the nomenclature of 

 Victor Audouin (Annales des Sciences Naturelles,tom. i. p. 119), 

 as being the simplest and the clearest : but other entomologists 

 have applied the same terms to different parts. The first seg- 

 ment is termed by Straus Durckheim and other French writers, 

 the Corselet. Mr. Kirby calls it the Manitrunk, and restricts 

 the term Prothorax to its upper portion. The united second and 

 third segments are the Thorax of Straus Durckheim, the Tronc 

 alift'rc of Chabrier. and the Alitrunk of Kirby. 



