Osten-Sacken: An essay of comparative Chaetotaxy. 137 
Myopidae. Macrochaetae almost undeveloped, hardly distin- 
guishable from hairs or minor bristles; undistinguishable in 
Conops; in Stylogaster a pair of conspicuous vertical bristles 
and distinct fronto-orbital ones. 
Dolichopodidae. Only one (outer pair) of vertical bristles ; 
a postvertical is so placed that it may be interpreted as the 
inner vertical pair. Ocellar pair very high on the vertex, 
between the vertical bristles and very conspiceuous. (za of the 
posterior orbit (Loew); Ahumeral (1), posthumeral (2), some 
intra-humeral (I), distinet supra-alar and ntra-alar bristles (II). 
In the dorso-central region two dorso-central outer rows; two 
(sometimes only one; Ziancalus) rows of small bristles, re- 
presenting the inner dorso-central rows, and which Mr. Mik 
has called the acrostichal bristles. (Dipterol. Untersuch. Wien, 
1878.) On the pleura, in Dolichopus, a characteristic pro- 
thoracic bristle. 
Asilidae. The cephalic bristles are indistinet among numerous 
hairs. A pair of ocellar bristles, and another pair, immedia- 
tely behind, are sometimes discernible. A series of oceipito- 
orbital (often stubble-shaped) bristles, are homologous to the 
cilia of the posterior orbit (Loew) of the Dolichopodidae. 
On the thorax , one (Leptogaster), or more, praesutural 
bristles (I) are characteristic; several supra-alar bristles on 
the post-alar callus (II); and a number of intra-alar bristles 
(Asilus); in Leptogaster, a very characteristie single intra- 
alar bristle (II). Often two longitudinal praescutellar rows 
of a few short bristles. On the pleurae, sometimes a few 
mesopleural bristles (Laphria), often hardly distinguishable from 
hairs, and a characteristic fan-like row of metapleural bristles. 
Empidae. The characteristic bristles are often, as in the Asi- 
lidae, indistinet among other hairs; but whenever these are 
less dense, some of the bristles become easily recognizable; 
one larger humeral, and several smaller ones; posthumeral 
bristles; a fan-like metapleural row, similar to that of the 
Asilidae etc. 
Bombylidae. It is only in a very few genera of this exten- 
sive family that the macrochaetae are differentiated m a more 
