comparative Chatotaxy. 517 



character is important, and of easy application in some 

 doubtful cases. Thus several forms described as Xijlo- 

 jjhagi may at once be recognised as not belonging there 

 by the presence of macrochaetae (for instance, X. hrun- 

 neus, Wied., which is a Therevid). On the contrary, 

 Lampromijla, which has no macrochaetse whatever, is a 

 Leptid, and not an Empid, as has been sometimes 

 contended. 



Nemocera. — All the families forming this artificial 

 group are destitute of macrochfetae. The stouter hairs 

 on the thorax and scutellum of Cnlex, and the bristles 

 on the legs of the MycetopJiilidce can hardly be considered 

 as such. 



The Gnlicidce, Chironomida, and TipididcB are dis- 

 tinguished by the development and the sexual differenti- 

 ation of the antennae, which are in this case very 

 probably the principal organs of orientation (as I have 

 shown above, on p. 500). The same conclusion may 

 perhaps be arrived at with regard to the Cecidomyidcs 

 and Mycetopliilidce . 



It is worthy of notice that Simulidce and Bihionida, 

 remarkable for the great sexual differentiation in the 

 structure of head and eyes (holoptic males ; differenti- 

 ation between upper and lower facets), execute aerial 

 dances, implying a power of regulating their flight. 



The BlepharoceridcB may be placed in the same group. 

 I have observed RJiyphiis (holoptic male) performing a 

 similar dance, which consists in a slow flight up and 

 down with outstretched legs. In all these cases we see 

 a confirmation of the connection I have adverted to 

 above between holoptic eyes, the power of regulating 

 the flight, and aerial life and dances. 



