EXTERNAL ANATOMY OF INSECTS. 371 



ii. Alttruncus (the Alitrunk). The posterior segment 

 of the trunk to which the abdomen is affixed, and 

 which bears the legs and wings a . It includes the 

 Mesothorax and Medipectus, and the Metathorax 

 and Postpectus. 



1. Mesothorax (the Mesothorax). That segment of 

 the alitrunk which bears the Elytra, or the anterior 

 pair of wings, and the intermediate pair of legs b . 

 It includes the Collare, Prophragma, Dorsolum, 

 Scutellum, Frcenum, and Pnystega. 



A Collare (the Collar). Thejirst or anterior piece of 

 the Mesothorax. In most insects that have a con- 

 spicuous Prothorax, as the Coleoptera, this piece 

 appears scarcely to have a representative ; but in the 

 Libellulina it co-exists with it, and is more con- 

 spicuous c . It is particularly remarkable in Hyme- 

 7ioptera and Diptera. 



B Prophragma (the Prophragm). A partition of an 

 elastic substance, rather horny, connected posteriorly 

 with the Dorsolum, which passes down into the an- 

 terior cavity of the alitrunk, of which it forms the 



" Plate VIII. Fig. 3, 4, 12—14, 16, 17- IX. Fig. 1, 3, 7, 8, 

 10—12, 15. ,J Ibid. r. 



•= Plate IX. Fig. 7, 11, 12, 15, 19. g. The Collare of Hymeno- 

 ptera and Diptera has usually been regarded as representing the 

 Prothorax of Coleoptera, Orthoptera, &c But this difference obtains 

 between them — the latter evidently belongs to the Manilrunk, and 

 its muscles do not appertain at all to the Alitrunk ; whereas the Col- 

 lare as evidently is a part of the latter, its muscles belong to it, and 

 its functions in assisting in flight are important. These reasons, and 

 others we shall state hereafter, induced us long ago to consider this 

 part as not representing the Prothorax ; and they seem to have in- 

 duced M.Chabrier almost to adopt a similar opinion. Sur le Vol des 

 Imectes. Ann. du Mus. 3cme Ann. 414. et 4eme Ann. 54 — . 

 2B 2 



