ON THE THOEAX OE THE BLOW-ELY. 9 



On the Thorax of the Blow-fly (Musca vomitoria). 

 By Aethtte Hammond, E.L.S. 



[Eead June 19, 1879.] 

 (Plates I. & II.) 



General Remarks and Descriptive Anatomy. 



The following observations on the structure of the thorax of the 

 Blow-fly embody a portion of the results obtained from a series of 

 investigations conducted by myself at different times within the 

 last few years on the thoracic structure of insects generally, and 

 are offered to the Society with some diffidence. 



Some time ago, on attentively considering the phenomena of 

 wing- development in that common pest of our cellars and kitchens, 

 the Cockroach {JBlatta orientalis), I was induced to form the 

 opinion that there exists in the prothorax of this insect parts 

 which, however disguised, are the true homologues of the wings on 

 the succeeding segments. My present object, however, is to submit 

 such evidence as appears to me to bear upon the problem of the 

 limits of the several segments of the connate thorax of the Di- 

 ptera as exemplified in the insect which gives the title to this paper. 

 So far as I am aware, our knowledge upon this subject has been 

 confined to the statement that, in common with the two other 

 orders of the Lepidoptera and Hymenoptera, the thorax of the 

 Diptera consists mainly of the central portion of the thoracic 

 region greatly enlarged at the expense of the other two. No 

 definite attempt though has been made to fix by any process of 

 reasoning the boundary which separates one of these segments 

 from the other. According to M. Audouin, referred to by 

 Newport *, " The parts capable of demonstration in each segment 

 are : — on the upper or dorsal surface, the prcescutum, scutum, 

 scutellum, and postscutellum ; on the inferior or pectoral surface, 

 a single piece, the sternum, and on the lateral, two pieces, the epi- 

 sternum and epirneron, on each side ; in addition to which there 

 are also two evanescent pieces, which are of considerable size in 

 some species, but scarcely distinguishable in others. These are 

 the paraptera, portions of the thorax not articulating with the 



* Article "Insecta," Cyclop, of Anat. & Physiol., p. 911, where Newport 

 summarizes from M. Audouin, Ann. d. Sci. Nat. vol. i. 



LINN. JOTJEN. — ZOOLOGY, VOL. XT. 2 



