36 MR. K. M. SMITH ON CERTAIN SENSE-OUQANS 



in either palp. In various Tachinids examined the pits are very 

 similar to those of non-pai^asitic Muscids. Of the Hippoboscidfe, 

 OrnitJwmyia appears to be poorly provided with antennal sense- 

 organs, having only a few thin sensory processes sunk in shallow 

 depressions, text-fig. 43. 



(VII.) Function. 



At different times very many entomologists have attempted to 

 settle the vexed question as to whether the antennae bear the 

 olfactory organs or no, by mutilation of the antennae or by 

 painting them with gum or some similar substances. It seems 

 to me that experiments like this cannot definitely decide this 

 question, relying as they do largely on statistics and thei^e being 

 of necessity so great an element of chance. Mclndoo (6), in his 

 paper on the olfactory sense of Hymenoptera, concludes that this 

 sense must be looked for elsewhere than in the antennae. He 

 says : " It is seen that about one-quarter of all the workers who 

 have experimented on insects with mutilated antennae assert that 

 these appendages do not bear the olfactory organs," On page 295 

 he states further : " It is now generally believed that the 

 antennae bear the organs of smell, but as all the antennal organs 

 are covered with a hard membrane the objection has been raised 

 that such organs cannot receive olfactory stimuli." I do not 

 think the term " hard membrane " is applicable to the.antennal 

 organs of the Diptera at any rate, as the sensory processes in the 

 pit are so excessively thin-walled as only to be visible under quite 

 a high power of the microscope. Berlese (1) states that a fluid 

 is secreted which passes through these processes and bathes the 

 interior of the pit. Packard (4) also says that these processes 

 are filled with a serous fluid and are definitely olfactory. 

 Personally I have never been able to find any traces of this 

 fluid. 



W. M. Barrows (7), iu his experiments on antennae, found that 

 gum on the antenna; of Drosoj)hila avipelophila does not keep out 

 odours. He etherised some flies and cut off the terminal antennal 

 segment (and he declares that the ether did not affect his 

 experiments). He writes : — " It seems certain that the sense 

 of smell is a.bsent or at least greatly reduced in those flies that 

 have lost the terminal joint of the antennae."' I emphasize the 

 word " terminal," because in all flies other than Nemocera it is 

 only in the third (i.e. terminal) joint that the sense-pits occur. 

 Wesche (5), who has studied this subject in some detail, writes: 

 " A number of experienced entomologists have separately come 

 to the conclusion that auditory organs exist in the antennae of 

 many species, and the deep pits or cavities in the antennae 

 of Muscids are thought to be such. This part then may be 

 a tactile, an auditory, or an olfactory organ in different species, 

 and it is probable that in many instances all three senses are 

 located, perhaps not exclusively but in part, in the antennae. 



