640 EXTERNAL ANATOMY OF INSECTS. 



observed a with regard to Jurine's bullae (bubbles), but 

 which are really the joints of the nervures, as they are 

 to be found only where the folds pass ; and where they 

 exist they are an index by which the folds, or rather se- 

 mifolds, may be traced. I counted eleven of these little 

 joints in the upper wing of Andrena cineraria; sometimes, 

 however, instead of a bulla, a nervure stops short to ad- 

 mit the fold. Wings in this Order have often three 

 longitudinal semifolds more or less conspicuous ; these 

 you may trace in the saw-flies (Tenthredo Ii.)> whose 

 wings Linne terms tumidce, by which term he would in- 

 dicate the elevation of the whole surface produced by this 

 structure ; in the under wings of these, and Scolia, Bern- 

 bex, &c, the Anal Area is turned under the wing, as in 

 many preceding tribes b : in Sirex, &c, that Area of the 

 upper wing turns upwards, forming an acute angle with 

 the rest of the organ; the same circumstance distinguishes 

 the under wing in the Ichneumonidce. Several apical 

 semifolds, marked by a pellucid streak, distinguish 

 Tiphia F., and in Bombus, Bembex, &c, an infinity of 

 branching ones, like those before described in Coleoptera, 

 corrugate the apical margin. In the Vespidce the upper 

 wings are folded longitudinally into three nearly equal 

 portions, but in the under ones the Anal Area only forms 

 the fold. 



In the Diptera Order, as to their position when at rest, 

 the wings are mostly incumbent one on the other; but in 

 Psychoda they are deflexed, so as to form a kind of pent- 

 house. With regard to their plication, in some, Tipula 

 oleracea, &c, a slight oblique semifold runs from the 



■ See above, p. 625. *> Ibid. p. 635, 637, &c. 



