642 EXTERNAL ANATOMY OF INSECTS. 



psiptera, Orthoptera, most Homopterous and many He- 

 teropterous Hemiptera, they approach to the quadrant of 

 a circle ; in a considerable portion of the Lepidoptera the 

 two under wings, if united at their posterior margin, ap- 

 proach a circular form ; the upper ones vary a little from 

 the prototype of the under ones, forming an obtusangled 

 triangle a ; in many Neuroptera the primary wings may 

 be called oblong or linear-oblong, while the secondary 

 betray more evidently the right-angled or obtusangled 

 triangle; in the Hymenoptera this latter form is every 

 where conspicuous, with little deviation, except in the 

 rounding of the angles b ; and, finally, in the Diptera this 

 form shades off again into an oblong, ovate, or linear 

 shape, the wing being most commonly attenuated at the 

 base into a kind of footstalk c . Some singular variations 

 with respect to the termination or marginal processes of 

 the wings are exhibited by many Lepidoptera ,• thus in 

 Attacus Atlas, &c, the primary wings are falcated or 

 hooked at their apex d ; and in great numbers both wings 

 are there scolloped into alternate bays and capes, if I 

 may so speak, varying in depth and length e . There is 

 usually a sinus between every pair of nervures, each of 

 which terminates in the adjoining prominence, as a fold 

 does in the sinus f . Where present, in the primary wings 

 there are eight of these sinuses, and in the secondary, 

 where they are most usual, seven; some are remarkable 

 for the long tails which distinguish their secondary wings; 

 those mPapilio are usually an elongation of the fifth, from 



J Plate X. Fig. 6. " Ibid. Fig. 8-11. 



• Ibid. Fig. 12—15. d Plate XIV. Fig. 4. 



-bid. biG.2. f I n Gastropacha quercifolia,&c, 



amongst the Nocturnal Lepidoptera, these sinuses exist, in the upper 

 vring ten, and in the lower nine, but without the folds. 



