PORIPHORA SPONGE OCEAN LIFE There are certain forms of organization so closely allied to both the animal and vegetable kingdoms, that it is difficult to say precisely in which they ought to be included. Such are the Sponges, which, although by common consent admitted. into the animal series, will be found to be excluded, by almost every point of their structure, from all the definitions of an animal hitherto devised. What is an animal ? How are we to distin guish it as contrasted with a mineral or a vegetable? The con cise axiom of Linnaeus upon this subject is well known :—" Stones grow; vegetables grow and live ; animals grow, live, and feel." The capability of feeling, therefore, formed, in the opinion of Linnaeus, the great characteristic separating the animal from the vegetable kingdom; yet, in the class before us, no indication of sensation has been witnessed ; contact, however rude, excites no movement or contraction which might indicate its being per ceived; no torture has ever elicited from them an intimation of suffering; they have been pinched with forceps, lacerated in all directions, bored with hot irons, and attacked with the most energetic chemical stimuli, without shrinking or exhibiting the remotest appearance of sensibility.
On the other hand, in the vegetable world we have plants which apparently feel, in this sense of the word. The sensitive plant, for example, which droops its leaves upon the slightest touch, would have far greater claims to be considered as being an animal than the Sponges, of which we are speaking. The best definition of an animal, as distinguished from a vegetable, which has yet been given, is, that whereas the latter, fixed in the soil by roots, or immersed perpetually in the fluid from which it derives its nourishment, absorbs by its whole surface the nourish ment which it requires ; the animal being, generally, in a greater or less degree capable of changing its position, is provided with an internal receptacle for food, or stomachial cavity, from whence, after undergoing the process of digestion, the nutritious matter is taken up. But, in the case of the Sponge, no such reservoir is found, and in its place we find only anastamosing canals which permeate the whole body, and convey the circumambient medium to all parts of the porous mass.—T. Rymer Jones.
In a work entitled "Principles of Zoology, by L. Agassiz and A. A. Gould," 1856, it is stated, " The Sponges have so great a resemblance to some of the polypi, that they have been classed among animals, although in reality they belong to the vegetable kingdom." Dr. George Johnson says :—" Sponge is a light, elastic, porous substance, formed of interlaced horny fibres, producing, by their numerous inosculations, a rude sort of net work, with meshes or pores of unequal size, and usually of a square or rounded angu lated figure. Besides these pores, there are some circular holes of a larger size (Oscula), scattered over the surface of most Sponges, and which lead into sinuous canals that permeate their interior in every direction. The oscula, canals and pores, com municate freely together, for the structure of the Sponge is alike throughout the mass, or at most the texture of the surface is merely a little more compact than the inner parts. The charac
teristic property of Sponge is the facility with which it imbibes a large quantity of any fluid, more especially of water, which is re tained amid the meshes until forced out again by a sufficient degree of compression, when the specimen returns elastic to its former bulk. From this peculiarity, combined with its pleasant soft ness, arises the value of Sponge, (the dried Sponge is only the skeleton of the living animal.) When the Sponge is living and recent, its canals and pores are filled with a glairy, colorless fluid, like the white of an egg, which flows freely out on the re moval of the Sponge from the water. The quantity of this fluid varies according to the species. In some it is copious, even to nauseousness, but in the compact Halichondriae there is little of it, and in the firm, inelastic, and calcareous Grantiaz it appears to be entirely wanting.". " It has an unctuous feel, emits a fishy odor when burnt, leaves a thin film or membrane when evaporat ed, and appears to the naked eye transparent, colorless, and homogeneous, like the colorless part of an egg ; but when a drop of it is examined on a plate of glass, under the microscope, it appears entirely composed of very minute, transparent, spheri cal or ovate granules, like monades, with some moisture. These monade-like bodies, nearly all of the same size and form, resemble the pellucid granules or vesicles, which Trembley has represented as composing the whole texture of the Hydrae, or the soft granular matter we observe in the stems of living Sertularim ; and, indeed, most of the fleshy parts of organized bodies appear to be com posed of similar pellucid, granular, or monade-like bodies in dif ferent states of aggregation." The composition of the skeleton or fibrous portion of the Sponge is remarkably diversified. Its liquid food is not received into any cavity, but permeates to all points, and is equally elaborated in every part of the system, which, in one sense, is an unconfined digestive cavity, where the various ingredients are selected, separated, and fitted for appro priation by each species, agreeably to its nature. For example, it is very common to find growing on the same rock or sea weed, a siliceous, a calcareous, and a horny sponge ; they have all the same exposure, and are all recipients of the same nutriment, yet does each act upon this differently. One extracts from the fluid silica, which it causes to assume a solid crystalline form ; another selects, in the same manner, the calcareous particles which obe dient to the laws of life, assume figures novel to them in their mineral state ; and, again, another rejects both the lime and the flint as injurious to its constitution. Sponges appear to be true Zoophytes, and it imparts additional interest to their study to consider them, as they possibly are, the first matrix and cradle of organic life, and exhibiting before us the lowest organizations compatible with its existence.