DISEASES OF INSECTS. 229 
and brocoli {Pontia Brassiccc\ which perish by hundreds 
from its attacks. As this falls frequently under our no- 
tice, it will not be uninteresting to give a fuller account 
of it. Reaumur has traced a\id related its whole history. 
One of these little flies that he observed, was so intent 
upon the business in which she was engaged, that she 
suffered him to watch her motions under a lens, without 
being discomposed. She pursued nearly the same plan 
of proceeding with that of the Ichneumon of the wheat- 
gnat just described ; except that she repeated her opera- 
tions frequently on the same caterpillar in different parts, 
alternately plunging in and extracting her ovipositor. 
She seemed to prefer the spot where the segments of the 
body are united, particularly where the eighth meets the 
ninth, and the ninth the tenth. When the fly had com- 
pleted its work and quitted the caterpillar, Reaumur 
gave it food, and it did not seem less lively and vigorous 
than others of its kind ; in less than a fortnight it as- 
sumed the pupa ; and in four days the whole of its inte- 
rior being devoured, it died : but its parasites, perhaps 
not finding a sufficient supply of nutriment in it, never 
came to perfection a . Sometimes, however, these little 
grubs arrive at maturity before the caterpillar has be- 
come a chrysalis, when they pierce the skin and begin to 
emerge. First appears a little white tubercle, which gra- 
dually elevates itself in a direction perpendicular to the 
body ; while this is doing, a second appears in another 
place ; and so on, till fifteen or sixteen are seen on each 
side, giving the caterpillar a very grotesque appearance. 
By the alternate contraction and relaxation of their bo- 
dies the grubs effect their complete liberation, which takes 
3 Reaum. ii. 417—. 
