comparative Chcetotaxy. 501 



therefore, that macrochtetse are organs of orientation, 

 connected with the nervous system, being in their useful 

 action not unHke the whiskers of a cat. 



We may go further, and connect this generalisation 

 with another one which I recommend to the attention of 

 observers. That faculty of poising seems, for some as 

 yet unknown reason, to be connected with contiguous 

 eyes in the male sex. Most of the above-named families 

 of Diptera eremochseta which possess that faculty {Taha- 

 nidce, Bomhiflidce, Syiphidce, &c.) have holoptic males (as 

 I will call them for brevity's sake). The Diptera chaeto- 

 phora hardly ever have holoptic males (even among the 

 Orthorhapha, as the Asilidce and Dolichopodidce), the 

 only exceptions, as far as I remember, occur among 

 certain Calyptrata (for instance, Hydrotcea, Ophyra, Ho- 

 malomyia), and it is very remarkable that just these 

 possess, more than their relatives, the faculty of regu- 

 lating their momentum. Diaphorus {DolicJiopodidce) is, 

 by exception, also holoptic. Thus we have on one side an 

 opposition between macrochfetge and eyes ; on the other 

 side a coincidence between macrochsetee and legs. 



The Diptera eremochseta, as I have shown, are for the 

 most part holoptic in the male sex ; at the same time 

 they are principally aerial insects ; they use their wings 

 for locomotion, their legs for alighting only {Stratio- 

 myidce, Bomhylidce, 'Tabanidce, most Syrphidce* &c.). 



On the contrary, the Diptera chgetophora use their legs 

 as much as, sometimes more than, their wings ; they 

 run, climb, snatch their prey, &c. (most of the Muscidce, 

 Phorida, ijoUclwpodidce, Asilidfe) ; in consequence, their 

 legs are much more developed and differentiated than 

 the legs of the eremochaeta, but the males are very 

 seldom holoptic. What a contrast, for instance, between 

 the soaring, bristleless, holoptic Bombylius, and the 

 bristly, pedestrian Phora ! 



These two groups do not, however, embrace all the 

 Diptera. The Tipididce, for instance, cannot be called 



'■' Among the Syrphidce, Chilosia, Clirysoclilamys, Volucella, 

 Bhingia, and Brachyopa have some macroch^tse on the sides of 

 the thorax and on the scutellum, but none on the head. Some 

 Syrpliidce., hke Xylota, are occasionally seen running upon leaves; 

 Grischner (Wien. Ent. Zeit., 1884, p. 200) makes the same ob- 

 servation on CaUijjrohola S23cciosa ; but these are exceptions to 

 the usual atrial habits of Syrphidce. Certain Bombylidce, like 

 Toxophora and Mulio, have conspicuous macrochaetse, and the 

 males are nevertheless holoptic. 



