But it by no means follows from the above, that all these fossil forms belonged to creatures whose species are wholly extinct. Indeed, in some instances, this cannot be allowed for a moment. Probably, the “choanite” is extinct. I doubt whether the “ventriculite” be so. Dr. Mantell was pleased to assume that this last-mentioned zoophyte _grew_—like one of the “mushroom” class of plants—rooted to one spot. There is no evidence for this whatever, and my impression leans another way. In the class of marine “Acrita” termed _Acalephæ_, there is a family which bears the name of _Rhizostoma_. These animals are composed mainly of a large, mushroom-shaped, gelatinous disc, and of a supporting central pedicle. In structure and function this latter organ much resembles the root of a plant; and, no doubt, it absorbs nourishment by seizing upon the minute animalculæ which abound in the water where the “rhizostome” is floating about. The entire animal is very like a toadstool, or “agaricus,” in form; but for all that, he does not grow, as a plant, in one spot, but is always sailing about by means of his large disc above-mentioned. His general appearance closely resembles that of a “ventriculite” from the flint; and I think it a probable guess to assign them to the same species. The “branching alcyonite,” on the other hand, did, I imagine, grow, like a Coral or “Encrinite,” in one place; and I suppose it was much like an ice-plant in form, but that it had the power of drawing back at will all its branches and suckers—which were, in fact, the creature’s arms and tentacles—into the root or bulb which formed its base. The “sponges,” a large family, we know are not extinct; and the conformation of the living individuals fully bears out all the marvels which have been predicated of the fossil animal. I have handled these creatures, fresh from the sea, at Brighton; and I had an unpleasant consciousness, while holding one in my hand, that the round, greenish, jelly-like bush was only his _house_; but that the gummy fluid, which held possession of it after squirting out the sea-water, was the individual himself, though independent of the accessories of bone and muscle. This kind of “sponge” floats about: there is another, well-known among submerged rocks, which is fixed, and grows. I believe the fossil specimens to have belonged to the migratory class. I once picked up, near Hove, a pebble which contained a fragment of the lungs of a tortoise; the elevated ridges, and depressed pulmonary cells, appeared to have left their peculiar structure in the flint. I have mislaid this specimen, and so cannot give a sketch of it here. The “holothurida,” or “sea-cucumber,” is found occasionally in the Isle of Wight, beautifully fossilized. A specimen was shown to me, from the beach near Chale; it was a _variety_, but unquestionably of this class of animals.