408 MR. J. G. H. FREW : MORPHOLOGY OF THE HEAD CAPSULE 
venh-al end of the stipites, whicli, as already mentioned, articulate with the 
base of the labrum. Although very near the surface I could not definitely 
determine that any part of these ventral ends was actually superficial. The 
stipites are flexible, and probably springy rods. When the proboscis is 
extended they are practically straight, but they are considerably curved 
when the proboscis is retracted. They probably iissist in the extension of 
the proboscis by pressing on the base of the labrum ; this point, however, 
requires further investigation. According to Peterson tlie areas mesad 
of the stipites are to be considered as developed from the submentum and 
mentura, while tlie areas lateral to them are formed from the maxillae. 
The Theca (fig. 5, th.) is a broad curved sclerite lying on the caudal aspect 
of the mediproboscis. It is not very heavily cliitinized, nor are its limits 
very sharply defined. On its dorsal (anterior) aspect the mediproboscis is 
channelled bj a longitudinal groove whose walls are rather more heavily 
chitinized than the general membrane of the mediproboscis ; the hypopharynx 
lies in this groove. 
Fig. 7. 
Diagram of the relationship of the epipharynx and 
the hj'popharynx. (Ventral view.) 
The Lahellce (Paraglossse) are shown in fig. 5. A detailed account of their 
structure is unnecessary as they are essentially similar to those of Mvsca. 
Each labella forms half of the stomal disc, the two being united mesially by 
a flexible membrane, and each bears three psetidotrachete. The two outer 
pseudotrachese of each side unite to form a short common duct which 
opens into a short but wide groove at the proximal end of the stomal 
disc, this groove being continuous proximally with the groove of the hypo- 
pharynx. The mesial pseudotraehea of each side opens separately into the 
short common groove. The glossse cannot be distinguished. According to 
Peterson this is also the case in Chloropisca, where " it is impossible to dif- 
ferentiate the glossae from the chitinized groove of the mediproboscis and the 
proximal ends of the pseudotracheaj " (p. 49). 
In the majority of Diptera each paraglossa is supported by a triradiate 
chitinized rod — the Furca — lying on its lateral and caudal aspects, and in 
the majority of Brachycera and Cyclorrhapha there is a small sclerite — 
Sigma — situated between each furca and the ventral margin of the theca. 
Neither of these sclerites is present in Chlorops, but this is not very surprising, 
as Peterson mentions a number of Diptera, Chloropisca among them, in 
