223] HEAD OF DIPTERA— PETERSON 53 



In a few cases, as in Borborus (Fig. 565 and 567), the liypopliaryux is 

 completely fused with the labium, while in others, as in Euaresta (Fig. 

 572), it is nearly so. In a majority of the genera the secondary separa- 

 tion of the lance-like portion of the hypopharynx from the basipharynx 

 corresponds with the similar separation in the epipharjTix. The shape 

 and size of the hj^jopharj-nx also vary considerably, as can be seen in 

 the figiires. In mouth-parts titted for sucking and piercing, the hy- 

 popharynx is usually long and needle-like ; while in licking forms (most 

 Calyptratae), it is greatly reduced. 



The salivary duct (s. d) enters the proximal portion of the lance- 

 like part of the hypopharynx and in most cases it is carried as a duct 

 or groove along the cephalic surface of that organ to the distal end. 

 The course of this duct or groove is indicated by broken lines in the 

 figures of the caudal aspect of the hypopharynx. The salivary duet 

 before entering the hypopharjoix is enlarged and bulb-like in many 

 species. In Tabanus (Fig. 494) the salivary bulb (s. b) is a chitinized 

 structure continuous with the hypopharynx, while in Promachus (Fig. 

 517) it is chitinized, but separated from the hj-popharynx. A chitinized 

 bulb and an enlarged membranous swelling are both present in Dolicho- 

 pus (Fig. 528). 



The peculiar epipharyux and hypopharynx of Olfersia (Fig. 606) 

 can be homologized with the more common types found thruout the 

 order. The principal difference is in the shape and position of the 

 basipharj-nx, the tormae, and the hyoid. The two lance-like structures 

 embedded in the deep membranous depression about the oral cavity 

 are the labrum-epipharynx and the lance-like part of the hypopharynx. 

 The long, crescent-shaped piece which extends cephalad from the proxi- 

 mal end of the labrum-epipharrax to the pear-shaped piece, is homolo- 

 gous with the hyoid (hy), and the pear-shaped piece with which the 

 hyoid connects is composed of the tormae (to) and the basipharynx 

 (bpli). The exposed parts of the tormae in the membrane ventrad of 

 the head are very small in this genus. 



Only rudiments of mouth-parts are found in the head of Gastrophi- 

 lus (Fig. 490 and 492). The anterior end of the alimentary canal is a 

 simple chitinized tube which leads to the small opening on the ventral 

 aspect of the head. This tube undoubtedly originated from the epiphar- 

 ynx and the hypopharynx. The mouth-parts are greatly reduced or 

 wanting. It is possible that the small bvdb-like structures located 

 latero-caudad of the opening are remnants of the labium. It is impos- 

 sible to homologize the other minute modifications surrounding the 

 mouth-opening. 



In the Cyrtidae, as Oncodes (Fig. 109, 486, and 487), the mouth- 



