Diptera: Nemocera vera^ N.anomala and Eremochaeta. 437 



the Nemocera vet^i, and I am not äware of any structure that may 

 be compared to tliem in other families. The erect hairs on the arista 

 of some Diptera, as in Ommatius, Sarcophaga, Drosoj^hila and 

 some Anthoinyiae and Ephydrina stand perhaps nearest to the sen- 

 sitive hairs of the Nemocera vera, but they differ frora them in being 

 inserted on the arista, and not on the Joint itself; besides, the sex- 

 ual differentiation in them is not apparent. They seem to come ne- 

 arer to organs of smell (especially in Drosophila and SarcopJiagaJ, 

 while the verticillate hairs of Culex have been hitherto interpreted 

 as organs of hearing (compare about the latter Chr. Johnson, Quart. 

 Journ. Micr. Soc. 1855, p. 97— 102, w. fig.; A. M. Mayer, Amer. Journ. 

 of science, Vol. 108, p. 89 — 103). The functions of the sensitive hairs 

 in the other families of Nemocera (Chironomidae, Tipulidae^ Ce- 

 cidomyidae) have, to my knov^'ledge, never been investigated. 



It would perhaps be more rational to adopt in this connection 

 a term that has been used by recent physiologists: the sense of „tre- 

 pidation" or Vibration. An instance of the effect of this sense was 

 communicated to me by a naturalist in Cuba, and I published a brief 

 account of it in the Stett. Ent. Zeit. 1861, p. 52: „when you stand 

 in the midst of a swarm of gnats, and a musical Instrument is soun- 

 ded in the vicinity, you feel that a certain tremor pervades the swarm 

 from tirae to time, so as to make a number of fhe insects to come 

 in contact with your face; this happens every time the note A (la) 

 is sounded." I have not had occasion to verify this Statement. 



In my „Essay on Chaetotaxy" (Trans. Ent. Soc. London 1884, 

 p. 500—502; also p. 517) I attempted to apply to the order of Dip- 

 tera the ideas suggested by Dr. A. Forel (Beitr. z. Kenntn. der Sinnes- 

 empfindungen d. Insecten, in the Mitth. Münch. Entom. Ver. II, 1878) 

 to insects in general. I have shown the contrast between the pre- 

 yailingly aerial Diptera, with a holoptic head, weak legs, and a few, 

 or no macrochaetae (Tahanidae, Bomhylidae, Syrphidae etc.) and 

 what I called the pedestrian Diptera, the majority of which have 

 a dichoptic head in the male, abundant macrochaetae, streng, well- 

 developed legs, with which they run, climb, snatch their prey etc. 

 (Asilidae, Dolichopodidae, most of the Calyptrata etc.). A third 

 type, the antennal Diptera, I recognized in what I now call the 

 Nemocera vera. 



The legs of the Nemocera vera, sometimes very long, are weak 

 in comparison to the legs of other families of Diptera; structural 

 peculiarities, useful for the Classification, are not abundant here. The 

 genus Ceratopogon in its broadcst sense forms an exception, and 

 shows a great variety in the structure of the legs. Sometimes the 



