The eggs deposited by the females in the oak buds in September remain there in a state of apparent quiescence till the following spring; then, as soon as the sap begins to flow, the irritant injected into the wound at the same time the _egg_ was deposited, or possibly the combined action of the egg and irritant, causes the sap to diverge; that portion of the bud which should have formed a young shoot is converted into a spherical ball; the outer scales of the bud fall away, and it is the woody secretion which entirely forms the gall. The cells in the gall are not elongated and regular, as in the young shoot, but confused and irregular; and in the centre of each gall lies a young grub of the _cynips_, forming a living nucleus, around which is deposited a thin, hard, woody envelope, much more compact in substance than the sponge-like tissue which fills up the interstice between it and the shining outer coat of the gall. This compactness of structure is a necessary and all-wise provision of nature for protecting the delicate insect which lies within from destruction; for if the gall were composed entirely of large spongy cells, the rapid flow of sap in the early spring would be more than the creature could consume, and it would consequently be drowned. I am aware that some naturalists incline to the opinion that the _larvæ_ of the _cynips_ feed on the gall. From this view, however, I venture to dissent; for not only is it inconsistent with the structure of the creature’s mouth, and the position in which the young _larvæ_ are invariably found, with the head tucked under the apex of the abdomen, but if they fed on the substance or crude material of the gall, the undigested parts would certainly be found in the interior of its cell: in other words, the excrement would be there, for there is no outlet, and the lacteals or absorbent vessels of the gall could not take it up. I therefore think that the creature feeds entirely on the sap of the tree—an elaborate food fit for it without the need of mastication. This explains how it happens that the galls of commerce, with the insects in them, are so much better and dearer than those from which the _cynips_ has escaped; in a word, the tannic acid is more abundant.