All the various kinds of _Foraminifera_ swarm in the present seas, and were not less numerous in the ancient ocean. We have seen that the white chalk almost wholly consists of a few genera of these animalcules; and in many strata of sand they are so abundant, that a cubic inch of the mass contains upwards of sixty thousand. In the _Rotalia_, the body is entirely enclosed within the shell, and occupies all the cells; and long, soft, tentacula are sent off through the foramina. The shell, therefore, though resembling in form that of the Nautilus, is essentially different; for in the latter, the outer chamber only is occupied by the body of the animal, the internal ones being successively quitted empty dwellings; whereas, in the _Rotaliæ_ and analogous _Polythalamia_,[AI] all the cells are contemporaneously filled by the soft parts of the animalcule. [AI] _Polythalamia, many-chambered_, is a general term applied to these shells. [Sidenote: RECENT FORAMINIFERA.] When the shell is removed, which is readily effected by immersion in diluted hydrochloric acid, the body is exposed, and found to consist of a series of lobes or sacs, united by a tube corresponding somewhat in its position with the siphuncle of the Nautilus, but which is the digestive canal. The body of a recent animalcule of this kind, deprived of the shell, is figured in _Lign. 23_. [Illustration: Lign. 23:--The body of a recent animalcule allied to the _Rotalia_, deprived of its shell; _highly magnified_.] Not only the characters of fossil shells of such infinite minuteness can be revealed by the microscope, but even the soft parts of the animalcules which inhabited them; for these are occasionally preserved, and may be demonstrated with as much distinctness as the recent examples.[AJ] In flint the soft parts of _Rotaliæ_, _Textulariæ_, &c., are abundant, and may be seen, with but little preparation, like insects in amber: the specimen figured in _Lign. 12_, p. 39, shews the body of a _Rotalia_ well defined; the only preparation this atom of flint has undergone, is immersion in Canada balsam. To detect such delicate structures in chalk requires, however, some experience in microscopic manipulation, as the calcareous matter must be dissolved in hydrochloric acid, and the animal substance separated from the residuum.[AK] [AJ] See '_Wonders of Geology_,' 6th Edit., p. 322. [AK] See my '_Memoir on the fossil remains of the soft parts of Foraminifera in Chalk, &c._' Philosophical Transactions, 1846, p. 465. Note VII. Page 43. _Isle of Wight Pebbles._ [Sidenote: ISLE OF WIGHT PEBBLES.]