

Orthorrhapha Bracliycera. 367 



and all kind of other work, seizing Ihcir prey, carrylng it, climbiiig, 

 digging etc.; tlieir legs are provided not only with spines and brist- 

 los, but with still other appendages, which niay be usefnl, or only 

 ornamental, as secondary sexual characters. 



I nientioned above the term pseudoholoptic head as distinct 

 from a true holoptic one. In 1884, not having yet nnderstood this 

 difference, I did not make any mention of it; since then I leai'ned 

 to appreciate its importance. True, complete liolopticisni, as that in 

 some male Tahanidae, Bombylidae, ('yrtidae, Syrphidae (among 

 the Cyclorrhapha), is alone connected with the faculty of hovering 

 in that pavticular fashion which distinguishes most genera of these 

 families. Pseudoholoptic heads, more or less incompletely con- 

 tiguous, occur in several pedestrian groups which, nevertheless, 

 have aerial habits, and thus, by adaptation, acquire an incomplete 

 degree of holopticism, They can swarm, soar, but they do not ho- 

 vor, like the niales of the other group. Nobody will contest that 

 JCmpidac, in their Organization, are truly pedestrian Diptera; at the 

 same tinie it is their aerial habits that tend to devclop their pseudo- 

 holoptic heads. The same is the case with Homalomyiai\ among 

 the Muscidae, well-known for the aerial dances of their raales; their 

 eyes are more or less contiguous, but their heads are not truly ho- 

 loptic, nor do such flies hover in the true sense of the word. 



Among all the orders of Insects, the Diptera display the greatest 

 variety in their modes of motion, and the greatest power of control 

 over their motions. It seems, thcrefore, rational that, by means of 

 the study of the motions in different groups of Diptera, we should, 

 in this Ordei', more than in any other, find indications towards the 

 discovery of corresponding differences in the Organization, and hence 

 a eine to a natural Classification. 



On the above-defined principlos of snbdivision, I now cstablish 

 two new Su 1)0 r families of the Orthorrhapha Brachyrrra: 



\. The Tromoptera for the aerial families: Nemesfrinidae, 

 Cyrtidac, Bo)nhyl>dae and l'lierevtdae (incliiding the Srcnopmhhte). 



The namo is derived from the Greok Substantive ö toÖho^, the act 

 of trembling (from rnffico^ I tremble), in allusion to the characteristic 

 faculty of hovering. which most of the Diptera of this family 

 posscss, a faculty that, as I have shown, seems to have some con- 

 noction with true holopticism in the male. 



2. The Ener^opodu for the pedestrian families: AfiiHdae, 

 DolirJiopodidae, Kmpidac (in the widest sense), Lonchopteridac 

 and probably Phoridae. 



