14. NATURE OF ZOOPHYTES.-In the larger and free masses of Flustra, the decomposition of the animal substance after death is very manifest. This specimen of Flustra foliacea, which was dredged up twenty miles SSW. of Brighton, in water eighteen fathoms deep, is a fine example of this brittle species; when first in my possession it was highly offensive from the emanations evolved during the decomposition of the animal matter.. It is now a flexible calcareous skeleton, with here and there portions of the shrivelled integument, but, of course, without any traces of polypes in the cells.

Let us now refer to our previous remarks, and inquire if the Flustra presents the essential characters of animal existence. Its polype possesses a determinate form, and has a calcareous skeleton covered by a soft fleshy substance, that can for a certain period resist chemical and mechanical agency. It is furnished with instruments capable of moving with great celerity, is susceptible of external impressions, and can expand and contract at will. Here, then, is evidence of sensation and of voluntary motion; and although, from the extreme minuteness of the structure, nerves cannot be detected, yet there can be little doubt that it possesses a nervous and also a circulatory system for effecting nutrition and reparation. We find, also, that, when removed from the element in which it lived, the creature dies, and its soft substance, like the flesh of the larger animals, undergoes putrefaction; it has lost the vital principle by which it previously resisted chemical agency, and now submits to the effects of those laws which act upon inorganic matter; the extreme. Organized beings, possessing life and all its functions, have been discovered so small that a million of them would occupy less space than a grain of sand. The malleability of gold, the perfume of musk, the odour of flowers, and many other instances might be given of the excessive minuteness of the atoms of matter; yet, from a variety of circumstances, it may be inferred that matter is not infinitely divisible.”—Mrs. Somerville, p. 125.

calcareous and horny materials that composed its skeleton, and which, like the bones of mammiferous animals, were secreted by the soft parts, alone remain.

I would here particularly remark, that the stony support of all Zoophytes is formed by a similar process; the hard substance called coral being secreted by the integuments or membranes with which it was permeated and invested, in like manner as the bones and nails in man are secreted by the tissues designed for that purpose, and acting without his knowledge or control. Nothing can be more erroneous than the popular notion that the cells of corals are built up by the polypes found in them in the same manner as are the cells of wax by the Bee.

From what has been advanced, it is evident that the Flustra is an aggregation of an immense number of individual polypes attached to a calcareous or horny skeleton, and each of which is doubtlessly susceptible of pain and pleasure independently of the whole; for we have a living proof in the Siamese twins,* that even in our own species there may be a united organization with separate nervous systems, and individual sensations; and, as it is certain that each polype enjoys distinct volition, it is most probable that the sensations of each individual are independent of the general mass. There is, however, a common sensibility pervading the structure that binds together the community of zoophytes, and by which certain actions are performed irrespectively of the individual polypes. Thus the compound zoophytes termed Pennatulæ, or Sea-pens,† upon the slightest touc withdraw themselves into the wet sand, and disappear: and the arborescent Vorticella,‡ upon the microscope being agitated, instantly shrink down into a globular mass, and all appearance of the elegant animalcules, a mo

* See the Philosophical Transactions for 1830, p. 177.

+ Belonging to the Alcyonaria.

See "Thoughts on Animalcules," p. 49.

ment before so active, vanishes. In certain species of Bryozoa (Bugula flabellata,* for example), each cell is accompanied by a bivalved appendage, much resembling in form the beaks and head of a vulture, and termed the "avicularium;" and these appendages open and shut apparently without the control of the polype that occupies the cell; their functions seem to be related to the horny axis that connects the group of independent living animalcules of which the entire compound zoophyte is composed, and not to the polypes themselves.+

15. THE CORALS, OR POLYPIFERA.-The Corals, or Polypifera (Zoophytes proper), present an extensive series of varied and extraordinary forms of zoophytal organization. In some, the skeleton‡ or support consists of various combinations of earthy and animal matter, as it is in the Flustra, but solid and hard as stone; in. many examples it branches out like a tree (Lign. 143, p. 624); in others, it constitutes hemispherical masses, having numerous convolutions on the surface, somewhat resembling in appearance the brains of quadrupeds (Lign. 144); and in many it forms an aggregation of tubes, terminating in star-like openings (Pl. VI. fig.

*Formerly known as Flustra avicularis. See Busk, op. cit. p. 44, pl. 51, 52.

†The reader will find some highly interesting observations on this phenomenon in Mr. Darwin's "Journal of a Voyage round the World," chap. ix. p. 200. Mr. Gosse has suggested that possibly the use of the avicularia may be to fortuitously catch and to hold minute animals until, attracted by their decomposition, hosts of other animalcules swarm in the neighbourhood and come within the currents produced by the ciliated tentacles of the zoophytes themselves.

The axis, framework, or skeleton of these groups of polypes is termed polypary, or polypidom (polype-habitation); and those of a stony hardness are familiarly known as 66 Coral:" these names therefore refer to the durable skeleton of the zoophytes, and not to the polypes themselves; but in familiar writing the term Coral is often used to designate the entire living mass. In a fossil state the polyparium alone remains, except in a few instances. See "Medals of Creation," chap. vii.

9). Among the branched varieties, some are covered by pores so numerous as to be called Millepora: in many, the openings are distant: some have star-like markings here and there; while in others, the whole surface presents a stellated structure. In many species the fleshy animal matter entirely covers and conceals the stony skeleton during life; in others, the latter becomes exposed, and forms a trunk, having branches covered by living polypes; while in another and numerous division (of which the common Sertularia is an example), the skeleton is flexible, and is secreted by the outer surface of the soft parts, and constitutes an external protection to the polypes (Pl. V. fig. 1). In another family, the Gorgonida (Lign. 145), the skeleton is of a horny or ligneous texture, and flexible, bending to the motions of the waves; while in some it is jointed or articulated, as in the Isis (Lign. 143, fig. 3). Sometimes the skeleton is impressed with the cells, as in the Madrepores (Lign. 143, fig. 2); while in other species, as the Red Coral, the stem is smooth, and exhibits no traces of the peculiar structure of the animal, the polype-cells being formed of the investing soft substance (Pl. V. fig. 9). Yet amidst all these varieties of form, the same essential characters are maintained; in all there is a skeleton or solid support, and a fleshy or gelatinous substance, either investing the polypidom and studded with polypes having more or less simple stomachal cavities; or constituting separate polypes, but more or less intimately connected by imtermediate animal and calcareous matter.

16. THE SERTULARIAN ZOOPHYTES.*. The Hydra, as above mentioned, p. 606, is regarded as the type of the Sertularian Zoophytes;† and, supposing it to be invested with a

* For the classification and description of the members of this group, the reader is referred to Johnston's "British Zoophytes," 2nd Edit.

+ There have been of late years discovered some remarkable points of alliance between these Hydroid zoophytes and the Acalephs (Medusa, &c.).

horny coat, to be elongated by growth, and to retain all the buds, or young Hydra, which are formed on its axis or stem throughout life, we might regard it as truly analogous to a Sertularia. The elegant arborescent Sertulariæ must be familiar to every one who has rambled by the sea-side. This branch of the Sea-pine (Lugn. 141), part of which is snown magnified in fig. 2, exhibits the usual appearance of these zoophytes. The Sertularia consists of tubes united together, and having lateral apertures for the protrusion of each polype; one elegant species, the Sertularia setacea, is very

LIGN. 141.-SERTULARIA NIGRA (JOHNSTON).

Fig. 1. Natural size. 2. A portion highly magnified (the tentacles not being protruded from the cells).

abundant on the shores at Brighton after storms, being attached to fuci and other sea-weeds. The representation of a branch, magnified sixty times, in Plate V. fig. 1, shows the form of the polypes, which, when fully expanded, are of great beauty. On one occasion, when I was present, Mr. Lister was observing a living specimen, when a little globular animalcule swam rapidly by one of the expanded polypes; the latter immediately contracted, seized the globule, and brought it to the mouth or central opening by its tentacula;