292 DISEASES OF INSECTS. 
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*. 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 
place, with respect to the whole, in less than half an hour. 
When entirely disengaged, they place themselves close 
to the sides of the caterpillar: even before this they be- 
gin.spinning, and draw unequal threads in different di- 
rections, of which they form a cottony bed, which serves 
as the base of the separate cocoon of each individual, 
which they next construct of a beautiful silk thread of a 
lovely yellow, which, if it could be unwound and in suffi- 
cient quantity, would yield a silk unrivalled in lustre and 
fineness ®. 
De Geer has recorded a very singular fact which de- 
serves your notice. An Ichneumon, appropriated to one 
of the Tortrices, had deposited its eggs in two of their 
caterpillars; each produced a considerable number ; but 
*, Reaum. vi. 417— b Ibid. 419—, 
