DISHASES OF INSECTS. QF 
yond the head; then with their ovipositor they pierced 
the body of the Aphis, at the same time carefully avoid- 
ing all contact with it in every other part: whenever they 
succeeded in their attempt, a tremulous motion of the 
abdomen succeeded. Only a single egg is committed to | 
one Aphis: when hatched, the latter becomes very smooth 
and appears swelled; it is, however, full of life, and moves 
when touched. Those that are thus pricked separate 
themselves from their sound companions, and take their 
station on the underside of a leaf. After some days the 
inclosed grub pierces the belly of the Aphis, and at- 
taches the margin of the orifice to the leaf by silken 
threads; upon this it dies, becomes white, and resembles 
a brilliant bead or pearl?. De Geer observed also an 
Ichneumon on the Coccus of the elm, J. Coccorum L». 
Amongst ithe Neuropterous tribes likewise, probably 
the Ichneumonide commit their usual ravages; but their 
exploits, as far as I recollect, have met with no historian. 
I have a small species related to Chelonus Jur., which:a 
memorandum made when I took it tells me was obtained 
from shna viatica; yet Ido not remember ever tracing 
that species to its final change, so that I must have taken 
this Ichneumon from the perfect insect. It suffices, how- 
ever, to prove that this tribe is also exposed to the attack 
of these parasites. Where larve and pupz are aquatic, 
it seems probable, if any attack is made upon them, that 
it must take place -_ they have quitted the water. 
In the Hymenoptera Order itself, almost every genus 
has been ascertained to have its Ichneumon parasites. 
Not even the fortified habitations of the gall-flies (Cy- 
* Leeuwenh. Epist. Oct. 6, 1700. De Geer ui. 869. 
> Lbid. 1. 604. - 
