412 Transactions of the Society. 



VIII. — Undescribcd Palpi on the Proboscis of some Dipterous Flies, 

 with Remarks on the Mouth-parts in several Fo,milies. 



By Walter Wesche. 



(Read June 18th, 1902.) ' 

 Plates IX. and X. 



Before describing what perhaps in our present knowledge may 

 be considered an abnormality, I propose to give a short account 

 of some more or less well known forms, graduating from those 

 which have nearly all the parts of the typical insect mouth, to 

 those in which many parts are absent, or apparently absent. 



Tabanus and Culex have all the mouth-parts present, with the 

 exception of what are usually called the labial palpi. But there 

 is a striking difference between the two, in the structure of the 

 labium. 



In the Gnat it is simply a horny sheath for the lancets, with 

 valves at the extremity, and covered with the scales characteristic 

 of the insect, fig. 1. 



In the Breeze Fly it is membranous ; the tip is tracheated, and 

 the organ has many points of resemblance to the labium in the 

 Muscidae, generally considered typical of the order, fig. 2. I have 

 said that with the exception of the labial palpi (the usual nomen- 

 clature), all the parts of the typical insect mouth are present : 

 the labrum, mandibles, maxillae with palpi, and the labium. In 



EXPLANATION OF PLATES IX. and X. 



The drawings were made from slides in the author's possession, the insects 

 having been cleared in caustic potash and mounted under pressure. Fig. 8 was 

 roughly sketched from a recently killed insect. 



Fig. 1. — Mouth-parts of Culex pipiens 9 (lateral view). 



(2. Mouth-parts of Hxmatopota pluvialis 9 (lateral view). 

 lb. Diagram of the same, ventral view with labium removed. 

 3. Mouth-parts of Empis chioptera 6 (lateral view). 

 ■i. Mouth-parts of Syritta pipiens <J (lateral view). 



5. Mouth-parts of Musca domestica 9 (dorsal view). 



6. Mouth-parts of Spilogaster flagripes 9 (lateral view). 



7. Portion of mouth-parts of Hyetodesia basalis 9 (lateral view). 



8. Sketch of mouth-parts of Hyetodesia perdita 9 seen as an opaque object. 



9. Mouth-parts of Dilophus albipennis £ (ventral view). 



The letters apply to all the figures, a, antennae. Ir, labrum. h, hypopharynx. 

 md, mandibles, m, maxillae. I, labium, p, palpi. Ip, labial palpi, mp, maxillary 

 palpi, r, rudiment. 



