versialists who have contended for scientific dominion over these bodies; naturalists of the highest eminence have been arrayed on each side. We shall content ourselves with giving the judgment of Dr Johnston, the learned. historian of British Sponges, and one well worthy of being listened to with respect; and we quote him the rather because his decisions, while they tersely exhibit the real merits of the case, have so yielded to accumulated evidence as to shift from the side first advocated to the opposite.

When the "History of the British Zoophytes" was published, the author omitted the Sponges, and gave the following summary of his reasons for so doing :-"If they are not the productions of Polypes, the zoologist who retains them in his province must contend that they are, individually, animals; an opinion to which I cannot assent, seeing that they have no animal structure or individual organs, and exhibit no one function usually supposed to be characteristic of the animal kingdom. Like vegetables, they are permanently fixed; like vegetables, they are nonirritable; their movements, like those of vegetables, are extrinsical and involuntary; their nutriment is elaborated in no appropriated digestive sac; and, like cryptogamous vegetables, or algae, they usually grow and ramify in forms determined by local circumstances; and if they present some peculiarities in the mode of the imbibition of their food and in their secretions, yet even in these they evince a nearer affinity to plants than any animal whatever." *

A few years later, however, the learned writer published his "History of British Sponges," in the introduction to

*Brit. Zooph., p. 29.

which he elaborately examines the whole question, concluding with the following verdict :-" Few, on examining the green Spongilla, would hesitate to pronounce it a vegetable, a conclusion which the exacter examination of the naturalist seems to have proved to be correct; and when we pass on from it to an examination of the calcareous and siliceous marine genera, the impression is not so much weakened but that we can still say with Professor Owen, that if a line could be drawn between the animal and vegetable kingdoms, the Sponges should be placed upon the vegetable side of that line.' We shall possibly, however, arrive at an opposite conclusion if, proceeding in our inquiry, we follow the siliceous species, insensibly gliding, on the one hand, into the fibro-corneous Sponge, filled with its mucilaginous fishy slime, and, on the other, into the fleshy Tethya, in whose oscula the first signs of an obscure irritability shew themselves. Sponges, therefore, appear to be true zoophytes; and it imparts additional interest to their study to consider them, as they probably are, the first matrix and cradle of organic life, and exhibiting before us the lowest organisations compatible with its existence."

Many of our readers are probably cognisant of only one kind of Sponge,-the soft, plump, woolly, pale-brown article, so indispensable in our dressing-rooms; or, at the most, two, if they chance to have noticed the large-pored, coarser sort with which grooms wash carriages. surprise such persons to be informed that the streams and shores of the British Isles produce sixty or seventy distinct species of Sponge; and that every coast, especially in the

* Brit. Sponges, p. 68.

It may

tropical seas, where they are very numerous and varied, has species peculiar to itself.

A Sponge, as it is used in domestic economy, is merely a skeleton : it is the solid frame-work which in life supported the softer flesh. This skeleton is composed of one or two of the following substances,—flint, lime, and a peculiar horny matter. The first two are crystallised, and take the appearance of spicular needles either simple or compound, varying greatly as to their length, thickness, shape, and curvature, but constant in form in the same species. The horny matter, of which the common domestic Sponge affords an example, is arranged in sleuder, elastic, translucent, tough, solid fibres, united to each other irregularly at various points, and in every direction, and thus forming an open netted mass commensurate with the size of the whole sponge. The horny Sponges are almost confined to the warmer seas, but the siliceous and calcareous kinds are common with us, especially the former.

The solid parts are, during life, invested with a glairy transparent slime, so fluid in most species as to run off when the Sponge is taken out of its native element; yet this clear slime is the flesh of the animal.

The spicula, whether of flint or lime, or the horny fibres, are so arranged as to form numberless pores, with which the whole animal is perforated; it is to these that our common Sponge owes its most valuable property of imbibing and retaining water, as we shall presently see when we investigate the history of this species in detail. In life the surrounding water is made to flow through these pores by a continual current (interrupted, however, at the will of the animal) from without into the interior of the

C

body. But whither goes this current? The pores lead into large channels, which also run through the body, like the drains from individual houses, which run into the main sewers; and these open on the exterior of the body by more or less conspicuous.orifices called oscula, or mouths. From these latter the effete water is poured in forcible streams, and thus a circulating current is maintained.

It was Dr Grant who first established the fact of this current from personal observation. His account of the discovery is full of interest. "I put a small branch," he observes, "of the Spongia coalita, with some sea-water, into a watch-glass, under the microscope, and, on moving the watch-glass so as to bring one of the apertures on the side of the Sponge fully into view, I beheld, for the first time, the splendid spectacle of this living fountain vomiting forth from a circular cavity an impetuous torrent of liquid matter, and hurling along, in rapid succession, opaque masses, which it strewed everywhere around. The beauty and novelty of such a scene in the animal kingdom long arrested my attention; but after twentyfive minutes of constant observation, I was obliged to withdraw my eye from fatigue, without having seen the torrent for one instant change its direction, or diminish in the slightest degree the rapidity of its course. I continued to watch the same orifice, at short intervals, for five hours -sometimes observing it for a quarter of an hour at a time, but still the stream rolled on with a constant and equal velocity." The vehemence of the current then began to diminish, and in about an hour ceased.*

No one can have looked with any attention at the rocks

*Edin. Phil. Journ, xiii. 102.