209] HEAD OF DIPTERA— PETERSON 39 



five segments and furthermore no piece is present at the base of any 

 generalized palpus which can be homologized with the palpifer of gen- 

 eralized insects. The greatest reduction in the palpus of the Nematocera 

 occurs in Geranomyia (Fig. 382), while in the Braehycera the palpus 

 of Mydas (Fig. 271) is a mere lobe. 



A small finger-like structure arises from the ventro-mesal margin 

 of each stipes and projects mesad to the caudal aspect of the hypo- 

 pharynx in Tabanus (Fig. 259) and Simulium (Fig. 258). These pieces 

 are apparently homologous with the laciniae (la) of generalized insects. 

 The distal ends of these projections articulate against the caudal aspect 

 of the hypopharynx (Fig. 496 and 497), and in this respect they differ 

 from the laciniae of generalized insects. These pieces in Tabanus have 

 been described as laciniae by Patton and Cragg (1913). 



A distinct lobe is present mesad of the palpus in the majority of 

 the Diptera that do not have a ptilinum. This structure is unquestion- 

 ably the galea (g), for in specialized insects which possess a distinct 

 galea the lacinia is generally reduced in size and in some cases wanting. 

 This tendency of development prevails in the Diptera. If the above 

 pieces in Tabanus and Simulium which are described as laciniae are 

 truly such, there can be no question regarding this interpretation of 

 the lobe adjacent to the palpus. The galeae vary considerably in size 

 and shape. They are long and needle-like in Tabanus (Fig. 259), in 

 the female of Psorophora (Fig. 266), and in Empis (Fig. 274), Exo- 

 prosopa (Fig. 285), and Eulonchus (Fig. 284a); while in Trichocera 

 (Fig. 260), Dixa (Fig. 262), Sciara (Fig. 267), Bittacomorpha, Chi- 

 ronomus (Fig. 270), Lonchoptera (Fig. 280), Scenopinus (Fig. 282), 

 and the male of Psorophora (Fig. 266) they are greatly reduced. In 

 Bibio (Fig. 264) and Geranomyia (Fig. 382) they are mere rudiments. 

 They are wanting in Rhabdophaga (Fig. 268), Tipula (Fig. 277), 

 Helobia (Fig. 385), Aphiochaeta (Fig. 278), Pipunculus (Fig. 279), 

 Platypeza (Fig. 272), and DoUchopus (Fig. 284). 



The development of the maxillae of the genera possessing a ptilinum 

 will now be considered. No cardines or laciniae are present in this 

 group. The maxillary palpi are one-segmented and are present in all 

 forms except Conops (Fig. 305). The palpi interpreted here as maxil- 

 lary palpi have been called labial palpi by some (e.g., Wesche, 1909). 

 The stipites and galeae are present in all the species studied, and they 

 undergo decided morphological changes. All connection or association 

 between the maxillae and the invaginations of the posterior arms of the 

 tentorium has been lost. This loss is even more pronounced than in 

 the Braehycera, since in all but a few species figured the maxillae are 

 far removed from the head and situated near the distal end of the 



