122 KANSAS ACADEMY OF SCIENCE. 



TABLE OF THE FAMILIES OF DIPTERA. 



BY PROF. S. "\V. WILLISTON. 



The following dichotomous table for the determination of the families of diptera 

 has been prepared in response to the requests of a number of correspondents who 

 desired some ready means of separating and classifying their material. It is intended 

 for the assistance of the general entomologist or beginner in dipterology more es- 

 pecially, and is in no wise a classificatory exposition of the subject, except in so far 

 as it separates families. 



The beginner will be much aided by having at his command a small collection of 

 determined specimens, together with a considerable material for comparison. Diffi- 

 culties to the inexperienced will often disappear with positive evidence before him, 

 where negative characters may be puzzling. In lieu of such material, or even with 

 it, the few following directions will be of assistance. 



Let him select for comparison a common large horsefly (Tabanidoi) and a com- 

 mon house or bluebottle-fly {Muscidce). By comparing the tip of the tarsi (feet) in 

 the two, he will immediately observe what is meant by the expression, "Empodia 

 developed pulvilliform." The middle membraneous appendage on the under side of 

 the claws in the horsefly is the pulvilliform empodium, while in the housefly the two 

 outer ones, the pulvilli, alone are present. The tarsus, composed of five joints, the 

 tibia, the femur, and the coxa, attaching the leg to the thorax, will be readily under- 

 stood. 



The antennae of the housefly will show what is meant by three simple joints, the 

 third of which bears the dorsal arista. The third joint in the horsefly, on the other 

 hand, will be seen to be "complex," that is, composed of a number of closely united 

 segments; it is also without style or bristle. The three, small, simple eyes {ocelli) 

 will be seen at the vertex in the housefly. The tegulte are flattened membraneous 

 scales, one overlapping the other, just back of the root of the wings, and covered 

 over by them; they are well developed in both flies. 



To understand the neuration, observe in the horsefly, near the middle of the wing 

 directed transversely, a large, oblong, five or six-sided cell, surrounded on all sides 

 by other cells. This is the discal cell, and is present in the majority of flies. In 

 nearly all cases, somewhere on the vein ( fourth longitudinal ) that bounds this cell 

 in front, will be seen a short connecting vein, directed anteriorly; this is the ante- 

 rior or small cross-vein, and affords, in most cases, a key to the neuration, no matter 

 how intricate. It always connects the fourth longitudinal vein behind with the third 

 longitudinal in front; the cell behind it is the discal, in front the submarginal, on 

 the outer side the first posterior, on the inner side the first basal. Lying parallel 

 with the first basal cell, and just behind it, is the second basal cell; just behind the 

 second basal cell is the third basal or anal cell. In the horsefly, the anal cell is seen 

 to run back obliquely to near the posterior margin of the wing, where it terminates 

 acutely, that is, the anal cell is said to be closed near the border of the wing; 

 should the two veins that close it run separately into the wing's margin, then the 

 cell is open. Now, counting outwardly along the posterior border to the third longi- 

 tudinal vein (posterior branch), there will be seen five posterior cells, all open (ex- 

 cept in a few species of our Tabanidon the first posterior cell is closed ), with their 

 bases bordering on the discal and first and second basal cells. By following the 

 third longitudinal vein outwardly from the anterior cross-vein, it is seen to give off 

 an anterior branch, which runs to terminate in the front margin or costa of the wing; 

 the third longitudinal vein is here furcate, and two submarginal cells are present. 

 Compare now these same structures in the housefly, and the discal cell is found much 



