Note aa — BOOK VIII.

Not only the Willow, and some other Trees, but Plants also, as Nettles, Ground-Ivy, &c. have Cases produced on their Leaves, by the Injection of the Eggs of an Ichneumon-Fly. I have observed those Cases always to grow in, or adjoining to some Rib of the Leaf, and their Production I conceive to be thus, viz. The Parent-Insect, with its stiff setaceous Tail, terebrates the Rib of the Leaf, when tender, and makes Way for its Egg into the very Pith or Heart thereof, and probably lays in therewith, some proper Juice of its Body, to pervert the regular Vegetation of it. From this Wound arises a small Excrescence, which (when the Egg is hatched into a Maggot) grows bigger and bigger, as the Maggot increases, swelling on each Side the Leaf between the two Membranes, and extending it self into the parenchymous Part thereof, until it is grown as big as two Grains of Wheat. In this Case lies a small, white, rough Maggot, which turns to an Aurelia, and afterwards to a very beautiful green, small Ichneumon-Fly.