6 F'amm.iks and Gkxkka ok 



behind by tlie vertical iimrj^tin, is known as the ocellar, or verti- 

 cal, triangle ; a similar triangle below, above the base of the anten- 

 nae, is called tiie kkontai. triangle. Below the antennae, the 

 space, limited by the oral margin, the cheeks and the eyes, is the 

 face, and characters drawn from it are of the highest value in spe- 

 cific classification. The space below the eyes, indefinitely limited 

 in front by the face, and behind by the margin of the occmmt (the 

 posterior surface of the head) is the cheek. Of the mouth-parts, 

 the rnoHOScis, when not rareh- absent, with its terminal, often fieshy, 

 scraping or suctorial flaj)s, the labella, and the one to five jointed 

 palpi at the base, is the most important. The oral margin of the 

 face is sometimes spoken of as the peristoma, or h y p o s t o m a, 

 but the more common and better term is epistoma. Of the antenna;, 

 the third joint, in the brachycerous and cyclorrhaphous diptera, 

 usually bears a bristle (arista), or style. 



The thorax is composed, as in other insects, of three parts, 

 the PKO-thorax, MESO-thorax, and META-thorax, but the first and 

 and the last are so aborted as to present but few anatomical charac- 

 ters. The prothorax is perhaps most readily distinguished in the 

 nematocerous flies, forming a rounded collar, back of the neck. 

 The metathorax is not seen at all from above; the scrxELU'M, a 

 semi-oval body behind, cut off by an impressed line, really belongs 

 to the mesothorax, the dorsum of which is often called the mesono- 

 TUM. Across, near the middle of the mesonotum, there is an 

 impressed line, terminating on each side a little in front of the wings, 

 that is known as the transverse sdture. The anterior su2)erior 

 angles of the thorax are the humeri, or humeral callosities, and 

 on the margin of the mesonotum, between the wings and the scutel- 

 lum, there is, on each side, an oval, obtuse i)rocess, named the post- 

 alar CALLUS. Limiting the mesonotum, running from the humerus 

 to the wing, is the dorso-pleural suture ; below it, the whole side 

 of the thorax forms the pleura, divided by sutures into smaller 

 spaces called the MESo-pleura, sTERNo-pleura, Hvpo-pleura, and 

 META-pleura. The under part of the thorax is the pectus or breast. 

 The oval, arched portion behind, beneath thescutellum, is the sieta- 

 NOTUM, and, on either side, we see a slender organ with a knob-like 

 head, the aborted second pair of wings, and known as the balancers, 

 poisers, or halteres. Above them, and back of the base of the 

 wings, are the more or less well-developed membranous scales, the 



TEGULiE. 



