IN THE ANTENNJ3 AND PALPI OF DIPTERA. 37 



Further, I found on the third joint of the antennae of Gastro- 

 philus equi a larger number of sense-pits than on any of the 

 flies mentioned [Helophilus jjendulus, Echinomyia fera, Thelaira 

 niyrijjes, Ckdlijihora erythrocephala, Stratiomys chamcdeon), and 

 of a different structure." As to tlie pits of G. equi being of a 

 different structure, I think Wesche is mistaken because, so far 

 as I could determine, they were very similar to the sense-pits of 

 other Diptera ; they were certainly numerous, though not in 

 my oj)inion as numerous as those of the Muscids. Wesche also 

 says : " I think that when the antennae are not particularly 

 sensitive the palpi have these structures to compensate." This 

 statement is borne out only pai'tially by the results of my 

 investigation (see above). Wesche states further : " We thus 

 see that the palpi like the antennae can bear organs of three 

 senses — touch, taste, and smell, but I do not think that any 

 one palpus has more than two of these senses developed at the 

 same time." He concludes : " (i.) Both the antennae and palpi 

 of insects are capable of receiving the stimuli of several senses ; 

 (ii.) Their capacities differ greatly in different species and conse- 

 quently a general rule is an impossibility." 



Packard (4) states definitely that these organs are olfactory 

 and agrees with. Berlese (1) in saying that the pit is bathed in 

 a fluid. 



Wheeler (2) describes what he calls olfactory and gustatory 

 sensilli on the third joint of the antenna?. He writes: " It seems 

 to be impossible to distinguish between tlie sense-organs in insects, 

 although it may be asserted that the organs of smell are situated 

 mainly or exclusively on tlie antennie, whereas those of taste are 

 found on the mouth-parts, especially on the maxilhe and labium 

 and their palpi." As stated above, I have not examined the 

 organ situated near the base of the antenna in certain Diptera, 

 known as the " Chordotonal Organ " or " Johnston's Organ " and 

 which is regai-ded as auditory by most workers. 



(VIII.) Systematic Description of the Sbnse-Organs 



IN THE VARIOUS FAMILIES. 



ORTHORHAPHA. NEMOOERA. 



TipulidtB (Text-figs. 1,2). Species examined : PachyrrJnna 

 histrio F. (C. G. Lamb det.), and one undetermined species. 

 One kind of special sensory structure or " Sensilhis " was found 

 to be present ; this is of the type described by Berlese (1) as 

 " Trichoid," that is, sunk in a pit but projecting up to or beyond 

 the general surface level. The shape of this sensillus varies 

 slightly in the two species examined, in one case being narrowed 

 to a point and having a distinct cap (text-fig. 1). The sensilli 

 are scattered more or less indiscriminately over the surface of 

 the antennae. In the palps no particular sensory apparatus was 

 apparent. 



Packard (4) states : " The olfactoiy pits of Tiimlids seem to 



