DIPTERA. 249 



The rounded body is compact, showing marked con- 

 centration of parts. The short, broad head (PL XII., 

 Fig. 197, A; Fig. 196) is attached to the thorax by 

 a pivot-hke neck. The prothorax (Fig. 197, ^') is 

 merely a Uttle collar-hke ring, but unHke that of the 

 Lepidoptera and Hymenoptera, is immovably consoli- 

 dated with the forward part of the mesothorax. It is 

 seen in PI. XII., Fig. 198, //, which is a drawing of 

 the head and thorax of another species of horse-fly. 

 Fig. 198, s\ is the prothoracic spiracle. 



The mesothorax (PI. XII., Figs. 196, 197, ^") is the 

 largest ring, and at first sight the whole thorax appears 

 to be made of this segment ; its chitinous scutellum 

 (Fig. 197, ts-) extends backward and slightly upward, 

 concealing the narrow dorsal portion of the metatho- 

 rax, as seen in PI. XII., Fig. 198, /r. Fig. 198, r, is 

 the mesothoracic spiracle. 



The metathorax (PI. XII., Figs. 197, 198, //") is 

 reduced in size, but is complex in structure. It con- 

 sists dorsally of the small ring just referred to (see Fig. 

 198, <^'"), which is uncovered by the abdomen. The 

 part usually called the scutellum (Figs. 197, 198, //) 

 is bulbous, and wholly concealed by the basal ring of 

 the abdomen (Fig. 197, C). 



The complexity of the thorax in the Hymenoptera and 

 Diptera has been the subject of much discussion among 

 entomologists, and the different opinions held in regard to 

 it are stated in a carefully prepared paper On Latreille's 

 Theory of "■ Le Segment Mediaire,^'' by C. C. A. Gosch.^ 



1 Naturhistorisk, Tidsskrift Schiodtc, Copenhagen, 3d ser., 

 XXX, 1883, pp. 475-531- 



