6 DIPTERA 
completely disappears. Within the family Empididz most of these transitions occur. Brachystoma 
has a long pointed anal cell, closed toward the margin of the wing, the posterior cubitus continuing its 
basal direction beyond the furcation. This is the primitive condition, possessed by the more generali- 
zed families. In Emfíisthe posterior branch of the cubitus is abruptly reflexed and forms the hind 
margin of the anal cell. In Climocera it is recurved rather than reflexed, but still is continuous with the 
under side of the anal cell. In Axthalia this vein forms a true crossvein, perpendicular to the two sides 
of the anal cell, apparently an intermediate condition. While this shortening of the anal cell isa mark 
of specialization it does not mean that the reflexed vein of Emfis has necessarily passed through a per- 
pendicular stage like that of An/halia. It probably had a sudden origin, or possibly passed through the 
rounded condition observable in Clinocera. The closure of the anal cell affords a most valuable charac- 
ter for the determination of the subfamilies of the Empididz. Those species with acute anal cell 
invariably belong to either the H ybotinz or the Brachystomatinze. The OOcydromiinz, except 
for Bicellaria, always have the perpendicular crossvein and this is likewise true of all the Tachydro- 
miinz that have an anal cell. The reflexed anal vein is preeminently an Empidinz characteristic, 
occurring outside of this subfamily only in one line of the Clinoceratinz and in Bicellaría. 
There are numerous tendencies evident in the Empididz to develop parallel structures. A 
strongly gibbous thorax, so characteristic of the Hybotinz, appears independently in Microfhorus, 
Bicellaria and Anthalia. The first vein is setulose in Oreogeton and PAleboctena, which are not close relatives. 
The pygidium is bent over the abdomen, forming an epipygium, in the groups about Clinocera, Hilara 
and Microphorus. Holopticism has been produced in numerous unrelated genera. The Empidide 
are further interesting in having extended the holoptic condition to the female, as in Syméallophthalmus 
and in most of the Hy botinz. Moreover the eyes may be enlarged below the antennze instead of above. 
This tendency is noticeable inthe Tachydromiinz, Hemerodromiine and Clinoceratinz, and 
in the extreme cases, such as Hemerodromia and Stilfon, the eyes quite touch on theface. The formation 
ofan arista is another example of homoplastic structures. The antenne throughout the family show 
much variation and afford a series of good taxonomic characters, which however should not be stressed 
as much as was done by Coquillett. In their generalized condition the antenne probably terminated in 
a short three-jointed thickened style. The basal joint ofthe style disappeared by coalition with the 
intermediate section, or apparently sometimes by fusion with the apex of the antenna, and in most forms 
the terminal part remained as a bristle-like segment, shorter than the preceding. This style has been 
replaced by an arista in many of the genera, but the mechanism of the change is obscure. The arista 
usually manifests a small basal joint and an attenuated outer portion, which corresponds to the original 
middle piece of the style. Among the most specialized genera of each of the subfamilies a lengthened 
arista is to be found. 
Metamorphosis. — The early stages of Empididze are relatively little known. — The larvz live 
as predators or scavengers in the ground or in rotting wood. Some have been found in the forests 
where the adults occur, some are semiaquatic, developing in mud. The species hibernate in the larval 
stage, pupating in early spring. : 
The larvze are cylindrical, more or less spindle-shaped, and comprise twelve segments. The 
head is small, retractile, eyeless, with the two-jointed antennze small but well developed. The labial 
plates and the longitudinal rods of the head meet angularly so that in profile they appear bent; 
mandibles lunate, maxillary palpi small, labium comprising two arcuate bands contiguous and angulate 
anteriorly. Prothoracic spiracles are small. Abdomen devoid of pseudopods or other appendages, 
most segments with transverse ventral swellings, the locomotor spinules forming bands on the anterior 
margins of the segments, the last segment more or less rounded, usually with a tooth or wart below on 
the hind edge and with a pair of large well separated and sometimes more or less elevated spiracles 
