364 bulletin: museum of comparative zoology. 



In the Nycteribiida, Streblidae, and male Ascodipteron the pro- 

 boscis is drawn back under the head and has little power of movement. 

 In the two latter the basal part is large, the dorsal plate of the labium 

 is sunk slightly beneath the edges of the ventral plate. These char- 

 acters are seen well in A. aviboinensis (Plate 3, figs. 28-29, vp. dp.) in 

 which the labrum-epipharynx is short and broad and bears several 

 large sense-pits (Plate 3, figs. 26-28, le.). The lateral edges of the dor- 

 sal plate of the labium, beyond the labrum, overlap and so form a tube 

 (Plate 3, fig. 29, dp.). The ventral plate is large and enfolds the dor- 

 sal plate, which, in a dorsal view, is covered by the lateral membranes 

 (Plate 3, figs. 26, 29, vp. dp. lm.). In the female A. speiserianum the 

 labrum-epipharynx is short and broad, with several large sense-pits. 

 The basal part of the dorsal plate of the labium is Y shape in section 

 (Plate 3, fig. 31, dp.), beyond the apex of the labrum the lateral edges 

 coalesce, the keel beneath becomes reduced and the dorsal plate forms 

 a complete tube in which the hypopharynx lies (Plate 3, fig. 32, hp. dp.). 

 The lateral edges of the ventral plate also meet and coalesce, except a 

 small basal portion (Plate 1, fig. 3, le, Plate 3, 30-31, lm.) from which 

 the greatly reduced lateral membranes stretch down to the edges of 

 the dorsal plate where they are in contact with the short labrum 

 (before they coalesce to form a tube (Plate 3, fig. 31, lm.). Thus the 

 dorsal plate, beyond the labrum, forms a complete inner tube and 

 the ventral plate a complete outer tube. 



The apex of the proboscis of flies is developed into a pair of organs, 

 the labellae, whose homologies are very uncertain and whose develop- 

 ment in the various families differs greatly. In most of the Cyclor- 

 rhapha they are usually well developed, lobe-like and membraneous, 

 capable of being brought together and folded away, or distended and 

 divaricated; they form the connection between the distal ends of the 

 dorsal and ventral plates and for our present purpose, may be regarded 

 as the distal development of the lateral membrane. Across the 

 surface of these organs radiate rows of incomplete taenidae, the pseudo- 

 tracheae, which undergo various modifications in different families. 

 In some of the Phoridae they are in the form of the letter U, the 

 prongs being pointed and turned outwards, and their bases fastened 

 to the membrane, along the inner surface are strong, two-pronged, 

 chitinous teeth. In a small Javanese scatomyazid there are several 

 large, strong, pointed teeth on the inner edge of the labellae, with 

 which it impales small insects. Among the Borboridae I find Limosina 

 vcnalicia with eight rows of small curved chitinous teeth, radiating 

 across the labellae. In most of the blood-sucking flies the labellae 



