THORAX OF THE BLOW-FLY. 27 



Fly, in which three principal masses are observable (PL I. figs. 9, 

 10, & 11), the anterior being the " sternali dorsaux " of Chabrier, 

 and the posterior his " costali dorsaux"; the intermediate one I 

 am uncertain about. 



Inasmuch, therefore, as there is no repetition, the muscles, I 

 submit, are those of one segment. Again, the central mass of 

 vertical muscles connects the anterior portion of the mesothoracic 

 scutum with the plate that Burmeister and Lowne call the meta- 

 sternum. How can this be ? There is only one answer. This 

 plate is not, as they regard it, metathoracic*. 



In addition to its muscular connexion with the mesothoracic 

 scutum, I would suggest the following reasons for regarding it as 

 the mesothoracic epimeron. "We have seen from Mr. Lowne's 

 account (op. cit.) that the prothoracic sternum sends out posterior 

 to the coxae two "cornua," which, passing outwards, expand into 

 small plates that surround the acetabula of the fore legs and reach 

 as far as the anterior spiracles (see PL I. fig. 2), the condyles, and 

 the lateral plates of the prothorax. In a perfectly similar manner 

 it appears to me that the mesothoracic epimera, if I may be 

 allowed so to call them, originate from the posterior extremity of 

 the sternum of that segment, and, passing outwards, surround 

 the acetabula of the intermediate legs, and are there brought into 

 contact with the spiracles, the sternum of the segment, and the 

 posterior lateral plates of Lowne, Audouin's episterna. It is a 

 character of Audouin's epimeron that it is always in connexion 

 with the coxa, and articulates with the sternum and episternum 

 of the segment f. Again, the posterior mass of vertical muscles, 

 the costali dorsaux of Chabrier, unites the posterior portion of the 

 mesothoracic scutum with Lowne's lateral plate of the metathorax 

 just above the posterior haltere. This, too, appears inconsistent 

 with the rule of muscular structure adverted to ; and I must 

 regard this plate also as part of the mesothorax, though I am 

 unable to identify it certainly with any of Audouin's pieces ; I 

 think it probably forms part of the postscutellum, together with 

 the central portion between the bases of the halteres. 



Thus it appears to me that the analogy of other insects, the 



* Antea p. 13. 



t Cyclop, of Anat. and Physiol., " Insecta," p. 48, for which reason also I re- 

 gard the above-mentioned cornua as the epimera of the prothorax, as stated 

 antea p. 14. 



3* 



