14 MB. A. HAMMOND ON THE 



the posterior spiracles, the plates between them and the wings, 

 and Lowne's metathoracic sternum (?). One portion, however, 

 has not yet engaged our attention, viz. the narrow plate between 

 the acetabula of the anterior coxse. This is called by Mr. Lowne 

 the prosternum. He says* : — " It consists of a central portion 

 and two cornua. The central portion is a long narrow plate 

 widest anteriorly ; it is grooved along the mesial line externally, 

 and presents a slight ridge internally; posteriorly it sends a 

 narrow plate along the edge of the mesosternum and between it 

 and the posterior edges of the coxae on either side. This plate 

 becomes broader externally to the coxa, and extends along the 

 outer edge of its articulation, reaching the lower anterior margin 

 of the anterior spiracle, where it unites with the lateral plate of 

 the prothorax, and terminates in a curved point in front of the 

 articulation of the coxa near its outer anterior angle behind the 

 condyle." 



The description appears mainly correct, though I shall have 

 occasion to differ from it in two particulars — first, the dissociation 

 of the condyles from the central carina between the coxa, owing 

 to their allocation in the "fifth or last cephalic segment" f; and, 

 secondly, the association therewith of the cornua, by which I un- 

 derstand the narrow plate which, as stated, runs along the edge 

 of the mesosternum, and which I believe to be Audouin's epime- 

 ron£. 



Lastly, we will look at the thorax from behind, having first 

 carefully removed the abdomen. Some of the parts already re- 

 ferred to appear again. Above is seen the scutellum, on either 

 side the posterior spiracles with the plates surrounding them, 

 and beneath are the coxae. In addition to these we have the two 

 capitate organs called halteres, which, as I shall show, take the 

 place of the posterior wings and a large surface of integument 

 lying between them, separated superiorly by a narrow membra- 

 nous conjunctiva from the scutellum, and having an emarginate 

 contour beneath to allow a passage to the viscera. A semilunar 

 space intervenes between its inferior margin and the lateral plates 

 forming Lowne's metasternum, into which project two slender 

 apodemes connected with the halteres. About the centre of its 

 length runs the junction of the first abdominal segment with the 

 thorax, which extends between the bases of the halteres and 



* Anatomy of the Blow-fly, p. 63. f Postea, p. 28. 



\ Postectfo. 27 (footnote). 



