There is still another method of uniting these animals together, more wonderful in its nature, and less analogous to any known principles of animation, and more difficult to perform. It is effected by introducing one within the other, forcing the body of one into the mouth of the other, and pushing it down so that their heads may be brought together: in this state it must be kept for some time; the two individuals are at last united, and grafted into each other; and the polype, which was at first double, is converted into one, with a great number of arms, and performs all its functions like another. The hydra fusca furnishes us with another prodigy, to which we know nothing that is similar either in the animal or vegetable kingdom. They may be turned inside out like a glove, and, notwithstanding the apparent improbability of the circumstance, they live and act as before. The lining or coating of the stomach now forms the epidermis, and the former epidermis now constitutes the coating of the stomach. A polype thus turned, may often have young ones attached to its side. If this be the case, after the operation they are of course inclosed in the stomach. Those which have acquired a certain size extend themselves towards the mouth, that they may get out when separated from the body; those which are but little grown, turn themselves inside out, and by these means place themselves again on the outside of the parent polype. The polype thus turned combines itself a thousand different ways. The fore-part often closes itself, and becomes a supernumerary tail. The polype which was at first straight, now bends itself, so that the two tails resemble the legs of a pair of compasses, which it can open and shut. The old mouth is at the joint as it were of the compasses; it cannot, however, act as one, so that a new one is formed near it, and in a little time a new species of hydra is formed with several mouths. Plate XXIII. B. Fig. 18, represents the upper part of a polype that has been divided into two parts; a, the upper, c, the lower part, the end c being something larger than that of a common polype, and is sensibly perforated; in the summer time this part often walks and eats the same day it is cut. Fig. 17, the other part of the same polype; the anterior end is very open, and the edges of it turned a little outwards, which afterwards folding inwards, close the aperture. This end now appears swelled, as at c, Fig. 21; the arms shoot out from this end: at first three or four points only begin to shoot, as at c, Fig. 20, and while these increase in size, others appear between them; they can seize their prey and eat before their arms have done growing. In the height of summer the arms will often begin to shoot in twenty-four hours; but in cold weather it will be fifteen or twenty days before the head is formed. Fig. 22, represents a polype that was cut close under the arms; this became also a complete animal in a little time.