The Bryozoaires, or Polyzoa, as British naturalists prefer to call them, form the boundary-line which divides the humble mollusc from the humbler zoophytes. In consequence of this intermediate organization, these creatures were long considered as polyps; but De Blainville, Milne Edwards, and Ehrenberg, almost simultaneously began to separate them from the molluscs, and form them into a separate group. Subsequent naturalists, while considering the Molluscoïda as truly and wholly molluscous, admit that the distinction proposed by the French naturalists is most important, and should be retained as a primary subdivision, confining it to those molluscs which have the neural region comparatively little developed, and the nervous system reduced to a single or at most a pair of ganglia, and the mouth surrounded by a more or less perfect circle of tentacles: an arrangement which would include the _Brachiopoda_ with the _Polyzoa_. Marine plants are sometimes observed to be quite covered with a velvety parasitic matter, which may at a first glance be mistaken for a moss. This, however, is simply an aggregation of animalcules, each of which has its separate cell, which is placed quite contiguous to its neighbour. These little creatures are thus entirely distinct. Each cell is formed by the skin, which has been encrusted by calcareous salts, or other organic matter, hardened after the manner of a horn. This kind of shell protects the animal from the attacks of its enemies. This mode of retreat at the bottom of a protecting shelter is very frequently adopted in the whole series of molluscs. The oyster shuts itself up by closing its valves, and the snail retires into its shell. This assemblage of small cells presented by the Bryozoaires has long been known as a coral. "We propose," says our author, "with very good reasons, to call it a _Testier_, or shell-builder." This testier, in which each shell has its opening, is furnished with a naked cushion, dentate, spinous, or protected by an operculum or lid, and presents itself under every variety of form. It is sometimes an assemblage of branching tubes, occasionally a rounded mass of spongy appearance, and now it presents itself as a flat lamelliform inarticulated expansion. In some of the marine species the shell of the mussel is covered as with a fine lace. It is a remarkable fact that these cells are not always inert. They seem to enjoy the power of motion. It is well known that the leaves and branches of the sensitive plant (_Mimosa_) contract and expand under the touch of the finger; the same phenomenon, according to Mr. Rymer Jones, takes place on touching the cells of certain species of Bryozoaires. The moment they are touched they quickly incline themselves; and the movement is immediately communicated from one to the other, until all the cells of the community are in motion.