INTRODUCTION. XXIII 



WINGS. 



To understand the neuration or venation of the wings the 

 student may select a common large horse-fly (Tabanidae). 

 Observe 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 nearly 

 all flies. Somewhere on the vein (fourth longitudinal'), that 

 bounds this cell in front, will be seen a short connecting vein, 

 directed anteriorly, the anterior or small cross-vein, which 

 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 vein in front (in a few rare 

 cases the second longitudinal vein); the cell behind it is the 

 discal, in front, between the second and third longitudinal 

 veins, the submarginal ; on the outer side the first posterior ; 

 on the inner side the first basal. Just back of the first basal 

 cell and separated from it by the fourth longitudinal vein, is 

 the second basal cell ; back of the second basal and separated 

 by the fifth longitudinal vein, is the third basal or anal cell. 

 Back of the anal cell and including the free posterior proximal 

 portion of the wing is the axillary cell. In the 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 closed near the border of the wing ; should the 

 two veins that close it run separately into the margin of the 

 wing, then the cell is said to be open. Counting from the 

 third longitudinal vein (posterior branch) backward along the 

 posterior border of the wing, to the vein that closes the anal 

 cell outwardly, the student will count five different cells, the 

 first of which, as already said, borders on the first basal cell, 

 the second and third on the discal cell, the fourth on the 

 discal and second basal cell, and the fifth on the second basal 

 and anal cells ; these cells are called the posterior cells, and 

 are numbered from before back; the first is bounded by the 

 third and fourth longitudinal and the anterior cross-vein ; the 



