W. WESCHE ON SOME NEW SENSE-ORGANS IN DIPTERA. 99 



2. Similar organs are to be found in a large number of the 

 Nemocera, Simulium reptans, Rhyphus fenestndis, and many- 

 others. These insects have not highly developed sense-pits on 

 the antennae. 



3. Pipimculns zonatus, Z., which has small and characterless 

 third joints of the antennae, has a well-marked sense-organ on 

 the tip of each palpus. 



4. Ocidromia glabricula, Fin., has large sense-organs on the 

 palpi, thjq- of an inch in diameter. The antennae are pilose, 

 having no sense-organs or pits larger than rroV o °^ an i ncn i n 

 diameter ; the third joint is only -ji^ of an inch in width and 

 g-| T of an inch in length. 



Weighing these facts, I think that where the antennae are 

 not particularly sensitive, the palpi have this structure to com- 

 pensate. We thus see that the palpi, like the antennae, can bear 

 organs of three senses — touch, taste, and smell ; but I do net 

 think that any one palpus has more than two of these senses 

 developed at the same time. 



I now come to certain sense-organs which I have found on 

 the legs of many species, but of whose function T can form 

 no idea. 



These consist of a membrane enclosed by a chitinous ring ; 

 on the membrane are a number of smaller rings, each support- 

 ing a delicate, sharply pointed hair. The enclosing ring of the 

 specimen figured in PL 6, Figs. 15, 19, is ^-^ of an inch in 

 diameter. For the sake of convenient reference I shall call 

 this " Structure A." It is situated on the inner side of the 

 trochanter of the middle leg of Aphrosilus raptor, Hal., and on 

 the same place in Poecilohothrus nobilitatus, L., is a homologous 

 organ. These are exceedingly delicate structures, placed in well- 

 protected spots, and probably capable of recording very slight 

 impressions. 



On the opposite side of the trochanter is a cluster of pits 

 without setae, and having below it a semicircular thickening 

 of the chitin (PL 6, Fig. 18). This I will call "Structure B." 



I have also found Structure A in two places at the base of 

 the second joint of the antenna of A. ruelijica, on workers 

 and drones, T iy by —^ of an inch in size ; on the same place 

 on the queen, but not arranged in ovals ; and also in front 



