The Mouth-parts of tin Kemocera. By //'. Wcschi. 7 



by muscles; the posterior end or hinge of the upper plate, when 

 this occurs, closes the pharynx, and so creates a vacuum : a 

 mechanism which differs from that of Culex. This is described 

 from A. crabroniformis (plate I. figs. 3, 4). 



An undetermined Asilus from Pegu shows a curious bulb fitting 

 into the right side of the lower plate, forming a valve; also a 

 membranous gland which runs down to what appears to he an 

 opening in the hypopharynx: judging from sonic remarks of 

 Professor Poulton on the instantaneous death of the prey of some 

 Asilids, this may be a poison-gland* (plate I. figs. 5-7)/ 



As I pointed out in the former paper, the Asilidse have 

 Xematocerous characters, and the presence of an organ found in the 

 older families is quite in harmony with that observation ; but, as I 

 shall show later, homologous organs exist in two other families in 

 the Brachycera, and form valuable proofs of affinity. 



The long labium of Chrysops ccecutiens L., which is figured in 

 plate iv. of the 1904 paper, is articulated by the membrane at the 

 base folding on itself, forming a fitting which holds the part in any 

 required position; a precisely similar arrangement is found in 

 many of the Empidse. 



(/roup 2. — The Empida? are such keenly predaceous insects 

 that the pharyngeal pump would be of value, and retained. I find 

 it in some species in my collection in various stages of develop- 

 ment. It is, however, used in a different manner, as there is a 

 piston working in the cavity which seems to be drawn back into 

 the pharynx ; this piston varies in shape in some genera ; in 

 Hybos I can see muscles attached to it. It seems absent in Empis 

 stercorea L., but I have preparations that show it in Hybos femo- 

 ratus Mull., H. grossipes L., E. Uvula L., Tachydromia cursitans 

 F., and T. maculipes Mg. (plate I. figs. 8, 9). 



I have observed that the inner tube of the hypopharynx in 

 If femoratus, E. stercorea, and several other species, is ciliated. 



The hard chitinised labium of Hybos shows a few " taste-cups " 

 — these structures are new to me on the labium of Diptera. The 

 labium in the Asilidse, which is developed on similar lines, bears 

 the usual " taste-hair," with a socket standing out of the supporting 

 chitin (plate I. fig. 10). 



In E. Ueicla, E. stercorea, and in those genera in which the 

 labium is long and membranous at the base, the membrane is 

 folded on itself and forms an articulation, precisely as in Chrysops. 



All the preparations of Empida? I have examined show the 

 mandibles fused into the mentum on the ventral side. 



'The mouth-parts of the Leptidse have several features which 

 were omitted in my previous description, and are of some 

 importance, as they show an affinity with several other families. 



* Predaceous Insects and their Prey. Tran-. Ent. Soc. London, Jan. 1907. 



