238 ON AN ICHNEUMONID LARVA 
reasonably ascribed to the quality of the food derived 
from a different species of spider; for it is a well- 
known fact that animal secretions are frequently 
modified in colour by changes of diet. 
It is deserving of notice that immature spiders 
infested with the larva of Polysphincta carbonaria do 
not change their skin. Were it not for this admirable 
provision of Providence, the larva, cast off with the 
integument in the act of moulting, would inevitably 
perish, and the important purpose which its remark- 
able economy is so evidently intended to subserve 
(namely, the keeping of these deadly enemies of the 
insect tribes within due limits) would fail to be 
accomplished. 
Various circumstances concur to render it probable 
that Polysphincta carbonaria deposits its eggs on 
spiders in the autumn, attaching one only to the 
abdomen of each individual. 
Messrs. Kirby and Spence, in treating on the dis- 
eases of insects in the fourth volume of their ‘ Intro- 
duction to Entomology’ *, have given a brief account 
of observations made by De Geer on the larva of a 
small Ichneumon discovered on a young spider, whose 
economy is similar to that of the parasite which has 
engaged my attention. 
Being desirous of ascertaining whether these insects 
were of the same species or not, and having no oppor- 
tunity of consulting De Geer’s celebrated work, I 
* Fifth edition, letter xliv. pp. 221, 222. 
