muir: two new species of ascodipteron. 361 



we can see the intermediate forms between the muscid and hippo- 

 boscid types (Plate 3, fig. 21). In Cyclopodia albcrtisi and Nycteribosca 

 amboinensis (Plate 3, figs. 22-23) the proboscis is situated far back under 

 the head, and has but a limited movement; the dorsal part of the 

 oral membrane forms the anterior part of the head, from which the 

 oral membrane stretches back to the base of the proboscis (Plate 3, 

 figs. 22-23, om). The same condition is found in the male of Ascodip- 

 teron spciserianum. In the female it is difficult to distinguish the oral 

 membrane, on account of the great expansion of the head, but it must 

 be the membrane between the face and gena and the proboscis. The 

 great expanse of oral membrane in the Muscids is mostly due to the 

 reduction of the clypeus and maxillae. 



The pharynx. The pharynx is the anterior part of the oesophagus, 

 highly chitinized, flattened dorso-ventrally, the lateral edges being 

 turned up to form the dorsal arms (Plate 3, figs. 20-30, da.). This 

 forms the fulcrum of many entomologists. In many of the Orthor- 

 rhapha (i. e. Culicidae, Bibionidae, Dolichopidae) the dorsal arms are 

 attached to the clypeus, which has little or no movement. This 

 type can be called the "fixed" pharynx. In some of the Orthor- 

 rhapha (i. e. Asilidae) the lateral edges of the pharynx are turned up 

 slightly but are not prolonged into dorsal arms and are not attached 

 to the clypeus; the pharynx is then "free." In the "protrusile" 

 type (i. e. Syrphidae, Muscidae) the clypeus is reduced to a small 

 strip, or to two or one small sclerites, situated in the oral membrane, 

 to which the dorsal arms are attached, or the clypeus is entirely lost 

 and the dorsal arms meet together in a point situated on the oral 

 membrane. In the "fixed" and "free" types the pharyngeal muscles 

 are attached to the clypeus, but when this is greatly reduced, or ab- 

 sent, as in the "protrusile" type, the pharyngeal muscles are attached 

 to the inner sides of the dorsal arms. 



In those protrusile types which are capable of the greatest amount 

 of movement, the basal part of the pharynx is prolonged into two long 

 " basal arms" for the attachment of the extensor and retractor muscles. 



The mechanism for the movement of the protrusile pharynx appears 

 to be of a simple nature, as shown in Plate 3, fig. 24. The pharynx, 

 a, b, c, is attached to the oral membrane at the point, a, on which it 

 can turn in a vertical direction; the retractor muscle is attached to 

 the point c and to the back of the head-capsule and the extensor to 

 the point c and to the head capsule near the oral margin. Upon the 

 contraction of the extensor muscle the point b moves through the arc 

 to 61, a being the centre of the circle. 



