the surface, like the Cirripedes; and others, as the Magillus and Serpulae, being attached to the surface, and lengthening their tube as the frondose expansions of the coral to which they are attached enlarge, so that they may be able to procure their fair share of nutriment, and not be starved, as they would be if the animal of the coral overtopped them.
These cases are common enough, but I have a specimen from the Rev. Mr. Guilding's collection which shows a much more uncommon instance. It is an expanded coral, which forms a thin surface on the top of another coral, and is furnished with a number of small, depressed, horizontal cases, opening with an oblong mouth. Some of these contain within them a small, free, crustaceous animal, a Cymothoa, which nearly fits the case; and it is evident, that by their moving backwards and forwards on the surface, they have caused the animal of the coral to form one of these cases for the protection of each specimen.
The animals which form their habitation in corals, appear to begin their domicile in the same way as the barnacles before referred to: they take advantage of the soft and yielding nature of the animals which form the corals &c, and taking up a lodgment in their body, all they have to do is to keep a clear passage in it, either by the moving backwards and forwards, the exertion of their limbs, or the ingress and egress of water to and from their bodies, and in time, as the coral is secreted by the animal, it will form a wall round them; but if, by any accident, the parasitic animal should not keep its passage from the coral to the surface of the body of the animal clear, which it must be constantly induced to do, since by this means it procures its food, the coral animal will in a very short time close over it and bury it alive in the mass of the coral; and this, from the number of these animals, of all sizes and in different stages of growth, which are to be found in the substance of the large and massive corals, must often be occurring. Thus the Italian romance is often literally fulfilled in Nature. J.E. Gray.
Notes on the vitality of the sheath of the Hydroidæ.
By R.Q. Couch, Esq., M.R.C.S.L.
An opinion is entertained by some naturalists that the polypidoms or solid parts of most zoophytes are extravascular and inorganic, and consequently, when once formed, are for ever placed beyond the
