IN THE ANTENNA AND PALPI OF DIPTERA. 35 



(y.) Situation of the Sense-Organp. 



In tliose families of Nemocera which have no antenna! sense- 

 pits, but only scattered sensory processes, these latter are found 

 on a number, if not on all, of the joints of the ilagellum. In the 

 Bibionidse, which have true pits, these were seen on a number of 

 joints of the flagellum (as well as on the palpi : see below), but 

 in the Brachycera and the Cyclorhaphous families antennal sense- 

 organs were only observed on the terminal joint *. As to the 

 palpi, pits were seen to be present on these oi-gans in Myceto- 

 philidfe, Bibionidse, and Therevidae; while special sense-organs 

 of a somewhat difterent form are described in certain Stratio- 

 myidse, Asilidse, and Dolichopidfe. Wesche (5) also describes 

 pits in the palps of Rhyphidje, Simuliidse, Empidte, and Pipun- 

 culidfe. He considers that when the antennal sense-organs are 

 not highly developed, those on the palpi are so, to compensate 

 for the deficiency. This is certainly true in some cases 

 (e. g. certain Mycetophilidae, Therevidae, and the families alluded 

 to by Wesche) ; but in some forms rather complex organs are 

 present in both antennae and palpi, e. g. in Blhio marci, certain 

 Stratiomyidie, Asilidae, and Dolichopidae. 



(VI.) Correlation between Form of Sense-Organs 

 AND Habits of the Flies. 



It was hoped tha.t after a systematic examination of the 

 antennal sense-organs of the Diptera, some definite correlation 

 between the form of these organs and the habits of the insect 

 would be found. Su^rh correlation, however, is not apparent. 

 Wesche (5) mentions the case of Gc(,st7'ophilas equi, the horse-bot, 

 coming up against the wind straight towards a horse, and points 

 out that this insect is well provided with antennal sense-organs ; 

 but so far as I have investigated, the Syrphidae have by far the 

 most complex and perfect sense-pits of all the Diptera,, and it is 

 not easy to see how their mode of life calls for this development. 

 There is also the case of Musca domestica and Calliphora vomi- 

 toria ; the former is supposed by some entomologists to find its 

 food chiefly by sight and the latter chiefly by smell, yet there 

 is very little difterence in the antennal organs of the two, except 

 that those of M. domestica are slightly moi^e complex, though of 

 course smaller in proportion. 



In some Hies possessed of very large eyes and keen sight, 

 e. g. Asilids and Empids, the sense-organs seem slightly smaller, 

 but in the case of the Muscidse both eyes and sense-pits are large. 

 The Asilids and Empids are predaceous, but their sense-pits show 

 no apparent modification correlated with this fact. As to flies of 

 parasitic habits, I have examined no Pipunculids, but Wesche (5) 

 found in a species of this family no pits in the antennae but a pit, 



* Tlie flagelliir " complex " of the Braclivcera is liere treated as a single joint. 



3* 



