VENATION : ANOPHELES 81 



vein. The marginal cell lies between the first and second, the first 

 submarginal between the second and third longitudinal veins, and the 

 second submarginal between the two divisions of the third longitudinal. 

 The discal cell, when present, is bounded by the fourth longitudinal 

 vein, and forms a convenient landmark from which to commence 

 studying the venation. Unfortunately, and this is one of the objections 

 to this system of nomenclature, a discal cell is denned as one in which 

 the boundaries are formed by veins alone and not partly by the wing 

 margin, and the cell answering to this description in one fly may not 

 always correspond with that in another in its relations to the veins. 

 Along the posterior border of the wing there may be one or several 

 cells, called the posterior cells and numbered from without inwards. 

 They are bounded by the posterior margin of the wing and the divisions 

 of the fourth and fifth longitudinal veins. Near the base of the wing 

 there may be two cells, limited externally by the anterior and posterior 

 cross-veins, and known as the first and second basal cells. The anal cell 

 lies between the fifth and sixth longitudinal veins, and the axillary cell 

 between the last longitudinal vein and the wing base, and corresponds 

 to the anal lobe. 



Certain other descriptive terms are in common use. When a cell 

 is bounded externally by the wing margin it is said to be open, and when 

 enclosed by the convergence of its two sides it is said to be closed. 

 A cell formed by the bifurcation of a vein, and therefore more or less 

 triangular in shape, is called a forked cell. The posterior basal cells 

 are sometimes termed the first, second, and third forked cells, as for 

 instance in most descriptions of mosquitoes, 



Notwithstanding the great deviations from the type which are found 

 in the various families, these systems of nomenclature are not so 

 difficult to work out as would appear from the foregoing account. 

 With the aid of an example of each, and of the accompanying figures, 

 the reader should be able to work out the venation in any of the other 

 families. 



In most descriptions of mosquitoes the older nomenclature is used, and 

 the wing of Anopheles (Plate XVII, fig. 2) may be taken as an example 



of this method. The costa, which forms the anterior , 



, . . -11 Venation of Mosquito 



boundary and is continuous around the apex with the 



thickened posterior border of the wing, presents no difficulty, nor does 

 the auxiliary vein behind it. The first longitudinal vein runs straight 

 from the base to the apex of the wing, without dividing. At the base of 

 the wing another vein arises just below it, and runs to the distal part of 

 11 



