THE ANATOMY OF INSECTS. 



21 



arrangement is described as the venation or neuration of the wing. The terms 

 veins and nerves are both in general use ; and when applied to the wings of 

 insects, have the same signification. Neither of them is good in this connec- 

 tion ; but they are so firmly established that it would not be well to try to 

 change them. The former, however, is the better. For in very many insects a 

 groove extends along the ental surface of the thickenings of each wall ; and the 

 groove of the dorsal and ventral thickenings being exactly opposed, form a 

 tube in the centre of each so-called vein or nerve, within which the fluids of 

 the body circulate. In many insects these tubes, or veins as I shall call them, 

 are also traversed by the air-vessels or tracheae. 



The thin spaces circumscribed by the veins are called cells. 

 An insect's wing is more or less triangular in outline; it therefore presents 

 three margins (Fig. 35). To these special names have been applied ; there is 

 however, a lack of uniformity among 

 entomologists in the terms which they 

 use. The cephalic margin, Fig. 35, 

 1-2, is termed the front margin, costal 

 . '/;, or simply the cdsta. The distal 

 margin, Fig. 35, 2-3, is known as the 

 outer margin, or apical margin. And 

 to the caudal margin, Fig. 35, 3-4, are 

 applied the terms inner margin and 

 anal margin. 



The angle of the wing at the union 

 of the cephalic and distal margins, 

 35. 2. is the apex of the wing; and 

 igle between the distal and cau- 

 dal margins, Fig. 35, 3, is the inner 



. The proximal end of the wing is referred to as the base. 

 With certain insects (Hymenoptera and some Homoptera) the cephalic mar- 

 )f the hind wings bears a row of hooks, which fasten into a corresponding 

 fold on the caudal margin of the front wings. These hooks arc named the 

 hdtnuli, and serve to hold the two wings of the same side together, thus insur- 

 thcir action as a unit. 



In the moths the wings are united in a somewhat different wav. On the 

 lower surface of the front wing near its base there is a hook formed of eii 

 portion of membrane or a tuft of hairs ; into this hook there fits a bristle, the 

 frintt/uw, which springs from the hind win^ near its base. The frcnulum is 

 simple in the males ; but it < ral bristles in the other sex. 



\in-s prevent many characters which are much used in classify 

 are variations in texture, form, clothing ami venation. 

 The most striking 'are are presented by the first pi 



Special names have been applied to the wings exhibiting the more 

 important of these These are 



The The term first paii 



ami These \v .r leather)', without veins or with 



merely traces of them, and when not in use they arc horizontal, and meet 



FIG. 35. Wing of Hepialus. 



