THORAX OF THE BLOW-FLY. 13 



M. Audouin's parapteron rather than his episternum. A similar 

 difficulty attends the identification of corresponding portions of the 

 thoracic casing of the Lepidoptera and Hymenoptera, whose con- 

 formation in many other respects runs somewhat parallel. Behind 

 this comes a succession of two or three smaller pieces, extending 

 beneath the wing, and perhaps doubtfully distinct from each other. 

 Thefirstof these only requires special notice, as it is this piece which 

 I look upon as Audouin's episternum. It will be seen that it, too, 

 may justly dispute the title with the piece in front of it, while its 

 situation under the wing brings it more into harmony with the 

 piece described by Audouin under the same name, and by Chab- 

 rier* under that of " clavicule scutellaire " in the mesothorax and 

 " plaque fulcrale " in the metathorax respectively, the anterior 

 superior angle running up in a point under the wing-socket, which 

 I regard as Chabrier's "appuis de l'aile." The remaining pieces 

 of the series extend between the alulet and the posterior spiracle. 

 Their precise relations I can say little about, save that, in common 

 with other parts forming the posterior surface of the thorax, I 

 purpose to show that they belong to the meso- and not to the 

 metathorax ; the last of them is Lowne's lateral plate of the me- 

 tathorax. There yet remain two pieces seen in profile, viz. the 

 sterna of the meso- and metathoracic segments, as they are re- 

 garded by Lowne. This designation is unquestionably correct as 

 regards the first, which i3 a large rectangular plate forming the 

 greater portion of the ventral surface, and marked by a groove in 

 the mesial line ; but with respect to the second I shall give reasons 

 for thinking that this also is mesothoracic and not metathoracicf . 

 It will be observed here that it is bounded superiorly by the pos- 

 terior spiracle, where it is broadest. Towards the mesial line it 

 is much contracted, and passes between the intermediate and pos- 

 terior coxae ; a portion of its anterior border also abuts upon 

 the sternum and another upon the episternum. The parts visible 

 on the ventral aspect have been already mostly described. In 

 front are seen the humeri, and between them the condyles of 

 Lowne ; then follow the anterior spiracles, the episterna of Lowne 

 (query, Audouin's paraptera ?) ; and between them the large ster- 

 num of the mesothorax, followed by the acetabula and coxae of the 

 intermediate and posterior legs ; and on either side of these are 



* See Chabrier, "Essai sur le Yol des Insectes," Memoires du Museum 

 d'Histoire Naturelle. 

 t Postea, p. 27. 



