the Superior Wing of the Hymenoptera. 443 



stant. Lastly we come to the variable group of cells 

 constituting Kirby and Spence's area intermedia, of which 

 the areolae mediae vary in shape and constancy much 

 more than the areolae apicales, though the latter are often 

 pellucid or wanting. Here are three distinct longitudinal 

 series of cells : those immediately beneath the radial are 

 the CUBITAL and vary in number ; beneath them are the 

 DISCOIDAL; and approximating the inner margin of the 

 wing are the ANAL at the apex and the BRACHIAL on its 

 basal side. I have been at some trouble to satisfy myself 

 upon the true relationship of the brachial cell ; usually it 

 has been considered to constitute one of the discoidal cells; 

 but I am strongly of opinion that it belongs to the area 

 basalis rather than to the area intermedia ; in any case it 



Fig. 4. — Diagrammatic Wing. 



must not be commingled with the discoidal, but stand alone, 

 in which case Thomson's name becomes most appropriate. 

 These cells are constituted by the intersection of the 

 wing tissues by sustaining " nervures," in reality true 

 circulatory veins. The front margin of the wing is always 

 bounded by a strong sustaining COSTA, which may or may 

 not be united with an adjacent and parallel POSTCOSTA. 

 The corneous stigma is a strong muscle to sustain the 

 more slender veins and assist in folding the wing. From 

 some part of it the RADIUS runs in a curve to or near the 

 apex of the wing. From the base two other elongate 

 nervures extend to beyond the centre of the wing ; the 

 posticus simply sustains the whole lower margin to the 

 sinus, but the MEDIUS is the central nervure and usually 

 goes direct to my point G ; beyond this it has usually been 

 regarded as distinct under the name of discoidal vein, etc., 

 but I find that in the very great majority of cases it is 



