STRUCTURE, DEVELOPMENT, AND BIONOMICS OP BOUSK-FLY. 403 



The Skeleton of the Proboscis. — The proboscis of 

 M. domestica is very similar to that of the blowfly, which 

 has been described by Kraepelin (1880) and Lowne (1895), 

 though the results of these authors differ in many details. 

 My study of M. domestica confirms Kraepelin's results, and 

 as Lowne's is the only complete account of the muscid head 

 a full description of its internal and external anatomy will 

 be given in this paper. 



Lowne regards the greater part of the proboscis as being 

 developed from the first maxilla} and not from the labium 

 or fused second maxilla?, which is the usually accepted view 

 and one which I support on morphological grounds. On 

 account of his exceptional conclusion he refuted the com- 

 monly accepted teinns for the various parts and invented 

 new ones. It will be necessary for the sake of descriptive 

 clearness to refrain from constant reference to these or any 

 discussion as to their value. 



The proboscis consists of two parts, a proximal mem- 

 branous conical portion — the rostrum and a distal half the 

 proboscis proper which bears the oral lobes. The term 

 haustellum is also used for this distal half (minus the oral 

 lobes), and as a name it is probably more convenient, as the 

 term proboscis is used for the whole structure — rostrum, 

 haustellum, and oral lobes. 



The rostrum (fig. 13, Ros.) is attached to the edges of 

 the proboscis aperture, that is to the epistomium, genas, and 

 the gulo-mental plate. It has the shape of a truncated cone, 

 and bears on the anterior side a pair of palps, which bear 

 sensory sette of two sizes. 



The haustellum (fig. 13, H.), or proboscis proper, is 

 attached to the distal end of the rostrum. The posterior 

 side is formed by a convex, somewhat heart-shaped sclerite 

 — the theca (figs. 1 and 3, th.) which probably represents 

 a portion of the labium. The lower angle of the theca 

 is incised by a semicircular sinus. By means of this the 

 theca rests on a triradiate chitinous sclerite — the f urea, which 

 consists of a median, slightly convex rod (fig. !,/.)> from the 



