W. WESCHE ON SOME NEW SENSE-ORGANS IN DIPTERA. 97 



pits, a few larger than the others, the larger being gl^ to y-^- 

 of an inch at their widest part, their shape being oval, but more 

 irregular than that shown in the diagram; (c) these pits are covered 

 with a delicate transparent membrane and appear to be enclosed 

 in a thicker or darker ring than the surrounding chitin. This 

 darkness, however, is possibly an optical illusion produced by the 

 angle at which the object is seen ; (d) on the larger pits are from 

 six to ten short styles or pegs. 



On PL 7, Fig. 7, I have drawn a diagram of the structure 

 as I imagine it to be when seen in section. This has analogies 

 with Kraepelin's diagram of the organs of smell on Melonatha 

 as given in Packard,* except that in the latter there is only 

 one style on the membrane, whereas in G. equi we find many. 

 The pits when seen from the opposite or inner side showed the 

 appearance drawn in Plate 7, Fig. 6, and some of the holes for 

 the insertion of tae styles were distinctly rectangular. 



At the base of the arista I discovered a sense-organ (PL 7, 

 Fig. 5), somewhat different in detail, which may not be of the 

 same function as those on the third joint. This had five styles 

 on the membrane, and was y-Vo of an inch in diameter ; it was 

 surrounded by a chitinous ring, but had no fine hairs round it. 

 I looked for similar structures on the Muscidae, but failed to 

 see any. 



On the third and fourth joints of the antennae of Stratiomys 

 chameleon, L., I found an analogous structure, with a layer 

 of rather more chitinised rods covering the pits, which were 

 disposed as shown in the diagram (Fig. 1, No. 6). The larger 

 pits are y-Vo °f an i ncn ni diameter, and contain a varying 

 number of styles. Why S. chameleon has this remarkable 

 structure on the antennae is not obvious. I am told it spends 

 a rather sluggish existence in the neighbourhood of the water, 

 where its larval state was passed. The mouth-parts are suctorial, 

 with the maxillae in a very atrophied condition. If the organs 

 described are olfactory, and we cannot be sure that they are such, 

 probably the high development of this sense enables the fly more 

 readily to find its mate. As these flies are not particularly 

 abundant, such a character would be of value. Apart from 

 the special case of S. chameleon, the whole family of the 

 Strat'omydae has very marked antennae, with numerous and 



* Textbook of Entomology, p. 275. 



Journ. Q. M. 0., Series II. — No. 55. 7 



