FAM. EMPIDID/E 3 
Phylogeny. — « These of course are not all the lines of evolution in Diptera, but I believe that 
they are all irreversible, that evolution has never recovered anything once functionally lost. Moreover, 
all, or nearly all these lines of evolution are polyphyletic, resulting in numerous cases of parallel resem- 
blances which must be taken into account in any attempt at /rue classification. » (S. W. Williston, 
Manual of Diptera, 3d. ed. p. 6r [1908].) 
The Empidida include more diverse forms than any other family of Diptera. There is no 
conservatism to an Empid type, indeed there is no Empid type. Between the full neuration of 
Brachystoma and the reduced venation of the highly specialized Tetraneurella there is so great a range of 
wing structure that one wonders why such diverse forms should be associated. 
By usual assent the Empidida have been grouped with the Dolichopodidz, forming a 
division of predatory flies called by Brauer the Orthogenya and by Verrall the Microphona. 
More or less nearly related to these insects are such families as the Asilide, Bombyliidz and 
Therevida, and more remotely in their ancestry such as the Leptidz and Rhyphidea. Characters 
occurring in the Empididze and also possessed in common by this series of families may usually be 
regarded as primitive. —Postulating thus, the ancestral Empid probably had wings with broadly 
rounded anal angle, the costa encompassing the entire wing and margining the large alula and calypter 
as well, the auxiliary vein distinct and complete, ending independently in the costa near or beyond the 
middle of the wing, the first and second veins simple and long, terminating toward the end of the wing, 
the third vein with a long fork, the pedicel of the second and third veins arising well toward the root of 
the wing, the discal cell complete and emitting three simple posterior veins, a strong thickening or fold 
in the wing membrane beneath the humeral crossvein, the basal cells long, the anal cell acute at its end 
since the so-called anal crossvein was not at all recurved. Moreover the following characters were 
probably indicated : head globular, eyes dichoptic and bare, proboscis short, antennz short, distinctly 
three-jointed, the last joint ovate-conical and terminated by a three- or four-jointed short style. Thorax 
small, the metathorax larger than the scutellum, no discal bristles, mesopleurz hairy, metapleurz bare, 
but velvety in front of the spiracle ; abdomen slender, long and cylindrical, pygidium symmetrical and 
small, no telescopic chitinized ovipositor. Legs simple, slender and elongate, without bristles or apical 
spurs. 
"There is of course no living Empid that combines these characters, nor is any such extinct form 
known, but it is not difficult to picture a delicate bodied insect four or five millimeters in length, with 
feeble powers of flight and with the structure given above. It would not be overstepping the bounds 
ot analogy to predicate further that this insect was of cinereous brownish coloration, had yellowish legs 
and hyaline wings, unmarked by a stigma, that it was predatory on smaller weaker insects and lived in 
shady woods to the North, the adults appearing shortly after the winter snows had disappeared. 
Evolution of the genera of the Empidida has proceeded along certain lines recognized as a 
usual trend in the development of Diptera. Holopticism or the further development of contiguity of 
the eyes of both sexes appear again and again. There is a frequent tendency to robustness, with gib- 
bous thorax, to the introduction of leg armature, specialization of the genitalia, development of meta- 
pleural setule. and of thoracic bristles, fusion of the basal joints of the antenne, a lengthening of the 
style into an arista, and a decided lengthening and specialization of the proboscis. In the wings there 
is a marked tendency toward reduction of the neuration, a shortening of the anterior and of the anal 
veins, thinning of the hind margin, suppression of the alula and diminution of the anal angle in one 
direction and lobation of it in another, and a shortening of the pedicels of the second and fourth veins 
and of the fork of the third. It is such trends as these that Dr. Williston had in mind in his words 
quoted at the beginning of this section. These tendencies toward specialization are not reversible : a 
fly with a forked third vein has not descended from one in which this vein is simple, for example, nor 
