THOBAX. OF THE BLOW-FLY, 15 



separates the superior or external portion from the inferior or 

 internal. 



The whole of this large surface forms Lowne's metathoracic 

 tergum*, so that, according to his view, we have the whole of the 

 pieces surrounding the thoracic abdominal foramen metathoracic, 

 viz. the metathoracic tergum and the lateral and sternal plates of 

 the same segment. That the same opinion was held by Bur- 

 meister appears from the fact that he recognizes the same plate 

 between the coxse as the metasternumf ; and his figures on 

 pi. xiv. of the thorax of Tabanus bovinus and My op a testacea 

 afford similar evidence. In assigning these plates, therefore, to 

 the mesothorax, I am conscious that I shall differ from a weight 

 of authority. "With respect to the posterior spiracles also, I must 

 differ from "WestwoodJ in assigning them too to the mesothorax 

 instead of to the metathorax, whilst agreeing with him in regard- 

 ing the halteres as appendages of the latter segment, in opposition 

 to Audouin and Latreille, who looked upon them as abdominal. 



So much for the external integument of the thorax. We must 

 now shortly notice the internal processes which form the ento- 

 sterna of the several segments. In the first place, we find the pair 

 which are found at the posterior extremity of the presternum and 

 reach the lower margin of the anterior spiracles ; they are re- 

 ferred to by Lowne§, and form, I believe, the prothoracic ento- 

 sternum||. Similar horny rami arise from the extremity of the 

 sternum in many Coleoptera : for example, in the mesothorax of 

 Geotrupes stercorarius, Dyticus mgrginalis, and Shizotrogus sol- 

 stitialis. The mesothoracic entosternum extends the whole length 

 of the sternal piece as a thin triangular vertical plate, with a pair 

 of lateral processes for the insertion of muscles. The entoster- 

 num of the metathorax arises between the posterior coxae and is 

 much narrower. A projecting point of integument between them 

 represents the whole breadth of Lowne's metasternum (my meso- 

 thoracic epimeron) in the mesial line. 



Now in deciding the question as to which segment any one of 

 the parts here described belongs, we may be guided by three con- 

 siderations : — 



1st. The analogy presented by other insects ; 



* Anatomy of the Blow-fly, p. 65. t Shuckard's translation, p. 85. 



\ West-wood's Introduction, p. 500. § Op. cit. p. 63. 



|| Posteh'p. 28, 



