362 bulletin: museum of comparative zoology. 



The pharynx of Hippobosca is of the protrusile type, but greatly 

 modified, probably owing to the flattening of the head and its position 

 on the thorax. The dorsal arms are large, the posterior ones reduced; 

 the anterior half of the pharynx is in the form of a thin, flattened, 

 highly chitinized, and elastic tube. A powerful extensor muscle runs 

 from the end of the dorsal arm to the base of the proboscis (Plate 3, 

 fig. 25) ; the stipites are articulated to the base of the labrum and at- 

 tached to the pharynx by muscles and form the radii of the arc (Plate 

 3, fig. 25, b, b) along which the proboscis travels when the extensor 

 muscle is contracted. The retraction is brought about by a muscle 

 proceeding from the base of the proboscis to the head capsule. This 

 is the chief movement made by the insect when feeding, but the 

 pharynx can be turned upon the point d as in other Calyptratae. 



In Streblidae and Nycteribiidae, owing to the shape of the head, 

 the proboscis is drawn back under the head (Plate 3, figs. 22, 23) and 

 the pharynx has a very limited movement. Hippobosca with the pro- 

 boscis retracted (Plate 3, fig. 20) and the head capsule around the 

 lower part of the oral margin cut away, would represent the position of 

 affairs in these two families. In the female Ascodipteron speiserianum 

 the pharynx is of the normal streblid type, but the dorsal arms (Plate 

 3, fig. 30, da) appear to be fixed to the edge of the head-capsule and 

 to have no power of movement. The enormous size of the proboscis 

 would prevent the small pharynx from moving it. The male pharynx 

 I have not been able to examine, but the head is so similar to Nycte- 

 ribosca that there can be little difference in the pharynx. 



The maxillae. The maxilla of Diptera has undergone a great 

 amount of reduction. It is found in its least reduced state in the 

 Orthorrhapha, where there is a distinct basal part, the stipes, a free 

 distal piece, the palpifer, 1 and a maxillary palpus. In some families 

 the papifer is lost and the distal end of the stipes is attached to the 

 labium (i. e. Empididae, Pipunculidae) to the labella (i. e. Dolicho- 

 pidae) or to the base of the labrum (i. e. Muscidae). In all the 

 Syrphidae that I have examined there is a free palpifer and in the 

 few Conopidae I know it is absent and the stipes is attached to the 

 base of the labrum. In some of the Acalyptratae (i. e. Drosophilidae) 

 there is a free palpifer, in others it is absent and the stipes are attached 

 to the base of the labrum, a condition found in all the Calyptratae, 

 Hippoboscidae, Streblidae and Nycteribiidae. According to Miiggen- 

 burg, Braula has a free palpifer, which is one of the reasons I cannot 



1 I use this term after Prof. J. B. Smith, it is the lacinia of Wasche, the lobus 

 maxillae of Hansen and the scalpellum of Meinert. 



