On the 8th of January last, while searching for hybernating Coleoptera in the woods near Ottawa, I had occasion to strip the bark of a decayed ash tree, under which, among other insect store, I found a small transparent and curiously-formed cocoon containing a larva of a fly which was at that time unknown to me. The cocoon was imbedded in the bark, occupying what I am now led to believe the excavation made by a grub of Cerambyx, or some other coleopterous bark-borer. when cocoons belonging to the genera Evaniidæ or Icheneumonidæ are found under bark of trees, or stones imbedded in the earth, we may safely assume that they are accompanied by parasites, and that the original possessor has been devoured because it was just the food that suited them.