ENTOMOLOGY. 113 



Lairs assume a lanceolate shape, and spring like small 

 leaflets from each side of the longitudinal nervures. 

 In assuming this form, they make an approach to the 

 scales of the Lepidoptera. These hairs, doubtless, 

 serve the purpose of preserving the wings from the 

 lacerations to which they would be exposed from the 

 nature of the places which the insects frequent for 

 food ; and, particularly, in the case of many of them, 

 when constructing their nests. In addition to this 

 use, M. Chabrier is of opinion that they may likewise 

 contribute to fix the atmospheric fluid on the wings 

 during flight, and thereby increase their buoyancy. 



The ribs alluded to, ramifying over the surface of 

 the wing, are properly called nervures. They are 

 horny tubes, whose office it is to support and give 

 tension to the membrane. A transverse section 

 shews that they contain a soft parenchyma, and a 

 large spiral vessel, accompanied by a fine nerve. 

 This spiral vessel is a genuine trachea, emanating 

 "from the cavity of the thorax, and therefore adapted 

 for conveying air throughout the wing. The nervures 

 are usually uninterrupted, but in some instances, 

 particularly among the Hymenoptera, (especially such 

 as have a petiolated abdomen,) their continuity is 

 frequently broken. This takes place chiefly at the 

 points where they anastomose with each other, and 

 the place where it occurs presents the appearance of 

 a small transparent spot, resembling an air bubble, 

 which led Jurine, who first noticed it, to call it a 

 ulla. The nervures there lose their tubular form, 

 nd become scattered in the shape of very fine 



