THORAX OF THE BLOW-FLY. 11 



called by Kirby * the collar was a portion of the prothorax or of 

 the mesothorax, a question which is, I believe, generally now 

 regarded as settled in the former sense. The different plates of 

 which the thorax is composed can be conveniently studied by 

 viewing them in their different aspects as seen from a dorsal, 

 ventral, or lateral, an anterior or a posterior point of view, as the 

 case may be. Let us first look at the thorax from an anterior 

 point of view, as seen on removal of the head. Surrounding 

 the cephalothoracic foramen on the dorsal surface is a slightly 

 thickened margin, the tergum of the prothorax (Burmeister's 

 pronotumf). A pair of rami project from it. On either side 

 of this are two small plates, bounded inferiorly by the coxa and 

 posteriorly by the anterior thoracic spiracle ; these are the lateral 

 plates of the prothorax, Audouin's episterna. The cephalothoracic 

 foramen is bounded inferiorly by two plates, which Mr. Lowne J 

 has called condyles, regarding them as parts of the last sub- 

 segment of the head. Prom this opinion, however, I must dissent, 

 as I shall have occasion hereafter to show§. Between the con- 

 dyles is a small plate forming a peculiar organ, which he has called 

 the cephalo-sternum, also looked upon by him as parts of the last 

 cephalic subsegment. All these parts are indicated in my 

 figure 5, PI. I. Let us now turn to the dorsal surface. Here 

 we find at its anterior angles two prominent portions, which in 

 many species are somewhat lighter in colour than the surround- 

 ing integument ; they are not marked off by distinct sutures, but 

 their extent is sufficiently indicated by their colour and their 

 protuberance. Burmeister (op. cit.) gives them the name of 

 humeri, and says they are the same as his pronotum||. Lowne 

 apparently does not notice them, or regards them as part of the 

 mesonotum ; for, speaking of the anterior spiracle, he says (I. c. 

 p. 72), " The mesothoracic tergum reaches over its superior 

 margin aud joins the prothorax in front of the spiracle.' ' 



It will be evident from a consideration of my figure 6, PL I., 



* ' Introd. to Entomology/ vol. iii. p. 548. 



t Burmeister's terms, pro-, meso-, and metanotum, as applied to the entire 

 dorsal surface of the respective segments, appear to supply a defect in Audouin's 

 nomenclature, and will be used in the course of this paper as occasion requires, 

 as also their opposites, viz. pro-, meso-, and metasternum. 



\ B. T. Lowne, ' The Anatomy of the Blow-fly ' (Lond. 1870). 



§ Po&tea, p. 28. 



|| Shuckard's translation, p. 82. 



2* 



