These are bred in an excrescence of a species of oak which grows in Africa, and are formed by a kind of fly, which bores into the bark of the tree, for a place in which to deposit its eggs. The sap of the tree hardens round the egg, grows with the growth of the tree, and becomes what we call the gall-nut, and which is used for dyeing. The worm that is hatched within this spacious vault, lives upon the substance of the ball, till after its change into a chrysalis and then a fly, when it eats its way through into the air, and gains its freedom.