Mr.Bowerbank*, however, has satisfactorily proved that some sponges possess a power of opening and closing the oscula at pleasure. He found that in a specimen of Spongilla fluviatilis about half an inch in diameter, which had attached itself to a watch-glass, there was at the summit of a large oval inflation a single osculum, which opened or closed according to the necessities of the animal, and from which, when in full action, a constant stream of water was poured forth. The inhalation of the water by the porous system presented some remarkable peculiarities: when in a state of repose, the dermal membrane appeared to be completely imperforate; but when about to commence vigorous inhalant action, a slight perforation appeared here and there over its surface, the orifices gradually increased in size until the full diameter of the pores was attained, and their margins then became thickened and rounded. On a little indigo being diffused in the water, it was seen to be absorbed with avidity; and the inhalant action continued for a considerable period, the interior of the sponge becoming strongly coloured with indigo.

A, a common Sponge: the arrows indicate the direction of the entrant and issuing currents.

Fig. 10. A, a common Sponge: the arrows indicate the direction of the entrant and issuing currents. B, a ciliated gemmule magnified.

* Quarterly Journal of Microscopical Science, vol. vi. p. 78.

After a time the rapid inhalant process ceased, either abruptly or~ gradually, a very languid action only remained, and nearly the whole of the pores were closed. When this operation was about to take place, the rounded margin of the orifice lost its form and became thin and sharp, while the circumference gradually melted inwards until the orifice entirely closed, and not a vestige of the organ previously existing remained: the operation of closing occupied rather less than a minute. When once closed, these orifices do not appear to be reopened, but fresh pores are produced. The colouring matter absorbed during the period of active inhalation was apparent in the sponge from twelve to eighteen hours; and during this period the stream from the osculum was extremely languid. The structure and habits of the freshwater Sponges are entirely in accordance with those of marine species.

(51). Prom this description of the structure of a sponge, it will be apparent that all parts of the mass are similarly organized: a necessary consequence will be, that each part is able to carry on, independently of the rest, those functions needful for existence. If therefore a sponge be mechanically divided into several pieces, every portion becomes a distinct animal.

(52). In Cliona celata, one of the freshwater sponges, M. Dujardin* discovered, mixed up amongst the pin-like spicula that constitute their skeleton, irregularly shaped globules, composed of a contractile glutinous substance, which, when examined under the microscope, were seen continually to change their shape, presenting a constantly varying outline, exactly similar to what is witnessed in the protean animalcule, Amceba diffluens, above described; and to this contractile substance, whereof the living substance of the sponge seems principally to consist, he proposed to give provisionally the name of Halisarca (sponge-flesh1.) Subsequent observations have shown that these proteiform bodies are not only thus changeable in their shape, but are able to exercise a distinct power of locomotion by agitating long flagelliform filaments that are appended to their bodies (fig. 11, l); in fact, the whole of the living portion of the sponge seems to be made up of agglomerations of these amorphous bodies, spread over the spicula or skeleton of the sponge, all individually capable of changing their form by emitting processes in different directions, so as to increase their means of contact with the surrounding fluid, from which they evidently derive materials for assimilation.

(53). These sponge-cells, as they are called by Mr. Carter 2, are about the 1/1000th part of an inch in diameter. If one of them be selected for observation, it will be found to be composed of its proper cell-wall, a number of granules fixed to its upper and inner surface, and towards its centre generally one or more hyaline vesicles.

* Ann. des Sc. Nat. torn. x. 1838. 1 Lit. "sea-flesh".

2 On the Freshwater Sponges of Bombay, Ann. Nat. Hist. 1849.

1. Remarkable forms assumed by Proteans developed from the matter of the seed like bodies of Spongilla.

Fig. 11. 1. Remarkable forms assumed by Proteans developed from the matter of the seed-like bodies of Spongilla, magnified. 2. General form of large spiculum. 3. Spiniferous spiculum. (After Mr. H. J. Carter).

(54). The granules are round or ovoid, translucent, and of an emerald-or yellowish-green colour, varying in diameter below the 1/13,000th part of an inch, which is the average linear measurement of the largest. In some cells they are so minute and colourless as to appear only under the form of a nebular mass, while in others they are of the largest kind, and few in number.

(55). The hyaline vesicles, on the other hand, are transparent, colourless, and globular, and, although variable in point of size like the green granules, are seldom recognized before they much exceed the latter in diameter. They generally possess the remarkable property of slowly dilating and suddenly contracting themselves, and present, in their interior, molecules of extreme minuteness in rapid commotion.

(56). The sponge-cell when in situ is constantly changing its form, both partially and wholly; its granules also are ever varying their position, in unison with, or independently of, the movements of the cell; and its pellucid vesicle or vesicles may be seen dilating or contracting themselves, or remaining passively distended, exhibiting in their interior the molecules above mentioned in rapid commotion. When first separated from the common mass, an isolated cell for a short time assumes a globular form, and afterwards, in addition to its becoming polymorphic, evinces a power of locomotion; it emits expansions of its cell-wall in the form of obtuse or globular projections or digital and tentacular prolongations. If in progression it meets with another cell, both combine; and if more are in the immediate neighbourhood, they all unite together into one globular mass. Should a spiculum chance to be placed in the path of a cell thus in motion, it will ascend it and traverse it from end to end, subsequently quitting it; or else, assuming its globular form, it will embrace some part of the spiculum and remain stationarily attached to it.