STRUCTURE OF INSECTS. Qoq 



segments in the cranium of insects; while Straus Durckhcim 

 considers it as formed by the consolidation of no less than 

 six segments of the vermiform larva. According to this 

 theory, the same elements which in the thoracic segments 

 are developed into feet, are here employed to form parts 

 having other destinations. From the segment adjacent to 

 the thorax the antennae are supposed to be developed. The 

 two anterior segments belong properly to the face; the one 

 giving origin to the mandibles, (m,) to the maxillae, or proper 

 jaws, (j,) and also to the palpi, (p;) the other producing the 

 processes called the labial palpi, (l. ) 



The mode in which the head is connected with the trunk 

 varies much in different insects. Sometimes it is united by 

 a broad basis of attachment, forming a joint between the ad- 

 jacent surfaces: but usually it is only appended by a narrow 

 filament, or neck; so that the articulation is effected by liga- 

 ment alone. Occasionally, it is placed at the end of a long 

 pedicle, which removes it to a considerable distance from 

 the trunk. In the HymenojHera and Diptera^ the head 

 moves upon a pivot, so as to admit of its being turned com- 

 pletely round. 



The trunk, or Thorax^ is composed, as shown in the figure, 

 of three segments, termed respectively the Prothorax (x;) 

 the Mesothorax (y;) and the Meiaihorax (z.*) The first 

 of these, the prothorax, carries the first pair of legs: the se- 

 cond, or mesothorax, gives origin to the second pair of legs, 

 and also to the first pair of wings, or to the Elytra (e,) as ia 

 the example before us; and the third, or metathorax, supports 

 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 



* In these denominations I have followed the nomenclature of Victor Au- 

 douin (Annales des Sciences Naturelles, torn. i. p. 119,) as being- the sim- 

 plest and clearest: but other entomolog-ists have applied the same terms to 

 different parts. The first segment 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 se^ents are the Thorax of Straus Uurckheim, the Tronc alt/ere of 

 Chambrier, and the Mitrunk of Kirby. 



