34 ILLINOIS BIOLOGICAL MONOGRAPHS [204 



is stylate, and the third segment is large and conical, with one or more 

 segments at its distal end. The antennae of Platypeza (Fig. 222), 

 Lonchoptera (Fig. 223), Aphiochaeta (Fig. 224), Oecothea (Fig. 227), 

 and Dolichopus (Fig. 226) show an advanced stage of development in 

 which the third segment is large and round and the remaining segments 

 are lash-like and situated toward one side of the third segment. All 

 but a few of the antennae of the Cyclorrhapha have apparently devel- 

 oped from a type similar to the last-mentioned genera. The principal 

 differences between the antennae of this group are in the length and 

 breadth of the third segment and in the modification of the arista. The 

 antennae of Olfersia (Fig. 249) are of a reduced muscid type, and are 

 inserted in deep cavities on the cephalic aspect of the head ; the scape 

 and pedicel are greatly reduced, and the arista is merely a small pro- 

 jection on the lateral aspect of the large segment. 



Antennal sclerites (a. s) are present only in Chironomus (Fig. 12 

 and 206) and Psorophora (Fig. 10 and 26). In these genera it is a 

 distinct chitinized ring about the proximal end of the scape. The extent 

 and place of the membrane with which the antennae are connected 

 vary considerably. In Trichocera (Fig. 16), Chironomus (Fig. 12), 

 Psorophora (Fig. 26), Mycetobia (Fig. 7), and some other genera it is 

 very extensive. 



A general survey of the antennae of the Diptera shows that in the 

 Nematocera they are generalized and on the whole resemble each other. 

 The specialized antennae of the Cyclorrhapha in all but a very few 

 genera are of a muscid type, and also quite similar in form. The 

 antennae of the Brachycera present a few specialized types, but the 

 majority of them show intermediate stages between the forms found 

 in the Nematocera and those of the Cyclorrhapha. 



Mandibles. — Only a few of the generalized Diptera possess mandi- 

 bles. They are present in the females of Simulium (Fig. 2 and 250), 

 Tabanus (Fig. 255 and 317), Psorophora (Fig. 159 and 251), Culicoides 

 (Fig. 253), Dixa (Fig. 254), and Bibiocephala (Fig. 155 and 256), but 

 wanting in the males of all the species examined except Simulium (Fig. 

 3 and 252). The males of Simulium johannseni and 8. jenningsi have 

 distinct mandibles. No other males of Simulium were examined. So 

 far as known this is the first record of a male dipteron possessing true 

 mandibles. 



The hypothetical mandibles (Fig. 256h) of a dipteron are long, 

 thin, sword-shaped structures fitted for piercing. They thus resemble 

 the mandibles (md) of Tabanus (Fig. 255) and Culicoides (Fig. 253). 

 They are situated between the clypeus, labrum-epipharynx, and max- 

 illae, and are closely associated with the invaginations of the anterior 



