DISEASES OF INSECTS. 207 
Mr. MacLeay, on the authority of M. Clairville, in- 
forms me) are particularly subject to this disease. But, of 
all the organs, the wings are most exposed to derange- 
ments of this kind. De Geer, in a specimen of Pieris 
Cratcegi just excluded from the chrysalis, observed that 
one of these was distended by a considerable quantity of 
extravasated green fluid — two or three large drops follow- 
ing'an incision. This disease appeared to arise from the 
lower membrane not adhering to the upper ; so that the 
nervures — which are rather longitudinal channels, being 
open below, than tubes — were not closed to confine the 
fluid to its proper course. The malady, which might be 
called a dropsy of the wing, carried off the insect the 
day after its exclusion a . Reaumur observed that the 
wings of some flies were affected by an «/r -dropsy, as he 
calls it, which appeared to arise from the air escaping 
from its natural channels, and thus separating the two 
membranes that form -the wing, and filling the cavity 
produced by their separation b . 
Sometimes also monstrosities are to be met with in 
these animals, or variations from a symmetrical structure 
in organs that are pairs. I have a beetle in which the 
terminal joint of one of the maxillary palpi is short, ovate, 
and acute ; and that of the other, long, semiovate, and 
rather obtuse. A specimen of Blaps mortisaga in my 
cabinet, taken by Mr. Denny, besides the terminal mucro 
of the elytra^ has a long diverging lateral one. Goeze 
had the larva of a Semblis brought to him in which one 
of the two fore-legs, though perfect in all its parts, was 
only half the length of the other c ; which he regarded 
3 De Geer i. 72—. b Retmm. iv. 342. 
c Naturf. xii. 224. /. v./. 8. 
