NouTH Ameuican Diptera. 7 



The term abi>omen is usually applied to the upper side of the 

 third priiuipal part of the inseet, only; for the underside we use 

 the term ventkk. At the terminal part of the male abdomen, are 

 the sexual ai)pendaj;es, to whieh the name hypopygiitm is applied. 

 In the female, the eorrespondinfj part is the ovipositor. 



To understand the neuration of the wings, let the student seleet 

 for eomparison a eommon large horse-fly (Tabanida?) and a 

 common house or blue-bottle fly (Muscida?). Observe in the for- 

 mer, near the middle of the wing, directed transversely, a large, ob- 

 long, five or six-sided cell, surrounded on all sides by other cells. 

 This is the discal cell, and is present in nearly all flies. Some, 

 wliere on the vein (foirtii longitudinal) that bounds this cell in 

 front, will be seen a short connecting vein, directed anteriorly ; this 

 is the anterior 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 sub.marginal, 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 ccU. In tlie horse-fly, 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 out- 

 wardly along the posterior border to the third longitudinal vein 

 (posterior branch), there will be seen five posterior cells, all open 

 (except in a few species of our Tabanidas the first posterior cell 

 is closed), with their bases bordering on the discal and first and sec- 

 ond basal cells. By following the third longitudinal vein outwardly 

 fw)m 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 house-fly, 

 and the discal is found much more elongated, the basal and anal cells 

 small, the third longitudinal vein simple, not furcated, and only one 

 submarginal and three posterior cells are present. Do not confound 

 the obliquely placed vein that nearly closes the first posterior cell 

 with the furcation of the third vein. The house-fly will also show 

 clearly the six longitudinal veins, the last of which runs obliquely 

 backward from the anal cell toward the margin, the fifth bordering 

 the discal cell behind, .the first and second running into the costa. 

 The first vein that terminat<?s in the costa (before the middle of 

 the wing) is the aixiliary. The vein that closes the discal cell 

 outwardly is the posterior or great cross-vein ; the vein that closes 

 the anal cell outwardly, the posterior basal cross vein. 



By comparing the tip of the tarsi (feet) in the two above-men- 

 tioned flies, the student will immediately observe what is meant by 

 the expression " empodia developed pulvilliform." The middle 

 membranous appendage on the underside of the claws (ungues) in 

 the horse-fly is the pulvilliform kmpodiim, while in the house-fly the 



