We shall only say a few words on the first mode of reproduction. The eggs, according to Ehrenberg, come to maturity in the _H. viridis_ at the base of the feet, where the visceral cavity terminates. They are carried during seven or eight days, and determine by their fall the death of the animal. When the Hydra has laid its eggs, according to M. Laurent, it gradually lowers itself until it covers them with half its body, which, spreading out and getting proportionably thin, passes into the condition of a horny substance, that glues the eggs disposed in a circle round the body to plants and other foreign substances. She ends her career by dying in the midst of her ova. Trembley has studied with great care the mode of reproduction by budding--a process which seems to prevail in the summer months. The buds which are to form the young polyp appear on the surface of the body as little spherical excrescences terminating in a point. A few steps further towards maturity, and it assumes a conical and finally a cylindrical form. The arms now begin to push out at the anterior extremity of the young animal; the posterior extremity by which it is attached to the mother contracting by degrees, until it appears only to touch her at one point. Finally, the separation is effected, the mother and the young acting in concert to produce the entrance of this interesting young polyp into the world. Each of them take with their head and arms a strong point of support upon some neighbouring body; and a small effort suffices to procure the separation: sometimes the mother charges herself with the effort, sometimes the young, and often both. When the young polyp is separated from the mother, it swims about, and executes all the movements peculiar to adult animals. The entrance into life and maturity takes place with these beings at one and the same moment. Infancy and youth are suppressed in this little world. So long as the young polyp remains attached to the mother, she is the nurse; by a touching change, the young polyp nurses her in his turn. In short, the stomach of the mother and her young have communication; so that the prey swallowed by the parent passes partially into the stomach of her progeny. On the other hand, while still attached to the mother, the little ones seize the prey, which they share in their turn with their parent by means of the communication Nature has arranged between the two organisms. In the course of his experiments Trembley states another fact still more remarkable. Upon a young polyp still attached to its parent he observed a new polyp or polypule, and upon this unborn creature was another individual. Thus three generations were appended to the parent, who carried at once her child, her grandchild, and great-grandchild.