638 EXTERNAL ANATOMY OF INSECTS. 
contrary, it forms its bottom. In the Trichoptera, the 
under wing being much more ample than the upper, the 
Anal Area forms a fold under the wing, and there seem 
longitudinal secondary folds besides. 
We now come to the Hymenoptera. In this Order 
the wings, as to their position in repose, are usually in- 
cumbent upon each other, and cover the abdomen; in the 
Vespide, however, they are placed parallel to the body, 
but do not cover it. Before I notice the plicature of 
these wings, I must recall your_attention to what I lately 
observed * with regard to Jurine’s bulla (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 (Serrifera), whose wings 
Linné terms tumide, by which term he would indicate 
the elevation of the whole surface produced by this struc- 
ture; in the under wings of these, and Scolia, Bembez, 
&c., the Anal Area is turned under the wing, as in 
many preceding tribes>: 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 Ichneumonida. Several apical 
semifolds, marked by a pellucid streak, distinguish 77- 
phia, and in Bombus, Bembex, &c., an infinity of branch- 
ing ones, like those before described in Coleoptera, corru- 
* See above, p. 624. > Jhid. p. 633, 635, &c. 
