468 ON THE THORAX OF WINGED INSECTS. 



halteres as representatives of the lower wings, and the alulae as 

 appendages of the upper wings ; consequently the part gene- 

 rally termed the scutellum, being attached to the alulae, will be 

 mesothoracic. Moreover, there is no distinct separation be- 

 tween the Dipterous dorsolum and scutellum of Kirby and 

 Spence, which generally exists. 



From these premises, I think we are fully warranted in re- 

 jecting the views of Messrs. Audouin, Latreille, and Kirby 

 and Spence ; and in considering — 



1st, The conspicuous portion of the thorax, immediately 

 following the large thoracic shield in the Diptera, as the meso- 

 thoracic scutellum. 



2d, The alulae of the Diptera as portions of the upper wings. 



3d, The posterior quadrate portion of the thorax of Tipula 

 as portions of the metathorax, and not abdominal. 



4th, The halteres as the representatives of the lower wings. 



And 5thly, (from the similarity of structure between the 

 Dipterous and Hymenopterous thorax,) That the terminal 

 portion of the thorax, which Latreille regards as " le premier 

 segment abdominal," is a portion of the metathorax. 



But in the greater portion of the Diptera, including the 

 genus Celyphus, we find the posterior portion of the thorax 

 in an apparently much less developed state. Examine a blue- 

 bottle, a gad-fly, or, better still, a Stratiomys or Helophilus, 

 and the thorax appears to consist of only two parts, — one large 

 square piece nearly covering the thorax, and another smaller 

 and semicircular, (and of a yellow colour in the latter genera,) 

 perfectly analogous to what I have termed the mesothoracic 

 scutellum in Chironomus and Tipula. On looking sideways at 

 the insect, the latter piece is seen to be elevated, and connected 

 with the first abdominal segment by a narrow arch, which is 

 dilated at the sides, and bears the halteres and metathoracic 

 spiracles. On carefully removing the abdomen, however, the 

 metathorax is found to be fully developed. 



Mr. Newman states that the basal abdominal segment in 

 Musca is so completely anchylosed with the metathorax, as 

 scarcely to admit the possibility of drawing the boundaries of 

 either. The very reverse of this is the case ; the metathorax is 

 deflexed and narrowed, and the basal abdominal segment raised 

 and dilated at the sides. It is impossible to confound them, 

 although the greater portion of the metathorax is internal ; 



