After I had puzzled in and out of the question, and that our play was ended, my uncle told me that sponges, of which there are now known more than a hundred different species, are found in a multitude of places, on the shores of both the old and new Continents. “Those most valued in the arts,” said he, “are inhabitants of the Mediterranean, and part of the Indian Ocean; two small kinds of sponge thrive even on the frozen shores of Greenland; and forty species have been discovered on the coasts of Great Britain. They are found equally in places that are always covered by the sea, and in those which it leaves dry with the ebb tide. They adhere to rocks, and spread all over their surface; in some places they keep possession of the most exposed cliffs, but they thrive best in sheltered cavities, and are found lining the walls of submarine caves, attaching themselves indifferently to mineral or vegetable, or even to animal substances.
“The size to which sponge attains is very uncertain; I lately saw an account of one found at Singapore in the East Indies, which was shaped like a goblet, and measured round the brim fifty-one inches; the stem was seventeen inches, and it contained thirty-six quarts of water! Naturalists have agreed to seven general divisions of form; so as to make something like an arrangement of this most singular class of organized beings.”
I interrupted my uncle here, to ask whether, in calling them organized beings, he meant the substance of the sponge, or the insects that are supposed to form it.
“It is curious,” replied he, “that two thousand years ago, the Greeks were occupied with this very inquiry; some endeavouring to prove the vitality of sponge, and others, to shew that it was merely the work of certain worms: and even so late as the year 1752, Peysonnel, the naturalist, communicated to the Royal Society a paper in support of this last opinion.
“Most naturalists, however, now agree in regarding sponge as a zoophyte, or a kind of animal approaching nearly to the form and nature of a plant; and Linnæus himself, latterly, classed it amongst animals. As the large orifices appeared to be the only means of entrance to the internal canals, it was supposed that the nourishment of this animal was drawn in through them; but later discoveries have shewn that, besides those apertures, there are minute pores over the whole surface; that through these pores the water is imbibed, by which the creature is nourished; and that the large round holes convey a constant stream of water away from the interior of the body. This stream carries off the particles of matter which are constantly separating from the interior, and which are not only perceptible by the assistance of the microscope, but may be occasionally seen by the naked eye, like small flakes. When a living sponge is allowed to remain a day at rest, in a white vessel filled with pure sea water, an accumulation of feculent matter is always found immediately under each orifice. If it is confined in the same basin of water for two days, the currents appear to cease; but, on plunging it again into water newly taken from the sea, they are renewed in a few minutes; and the continual circulation of water through the body, Dr. Grant, who appears to have studied this subject with great perseverance, says, he no longer doubts, forms one of the living functions of this animal.
“It would only burthen your memory,” continued my uncle, “were I to tell you all the various opinions which have been formed respecting the anatomy of the sponge. I will merely say, that Dr. Grant affirms, though in opposition to M. Cuvier, that the fibrous part of the sponge, which is insoluble in water, and forms a net work through every part of the body, is the skeleton of this zoophyte, serving, as in other animals, to give form to the body, and support to the softer organs.
“Sponge attaches itself sometimes to marine plants, so as to choak up their pores. Small bits of the same species will spread towards each other, and become one piece; and it is amusing to observe, says Dr. Grant, the growth of the young Spongiæ parasiticæ on the back and legs of a species of crab, where they frequently collect to the number of forty or fifty, interrupting the motion of its joints, and spreading like a mantle over its back, or perhaps rising in fantastic ornaments upon its head, which the crab is unable to remove.”
21st.—When I parted from Mrs. P. at Falmouth, my uncle, who was much pleased with her kindness to me, made her promise to pay a visit here in some little time. That time has, at last, come. We have her now actually in the house, and I have once more the pleasure of being with a friend who was so kind and tender to me when I left you, my beloved Mamma.—How many little circumstances are recalled to my mind by seeing her! She has just the same quiet composed look that she used to have; and, though always ready to converse and to impart the information she possesses, yet her countenance seldom loses a certain expression of sadness.
She arrived last night, and has promised to stay till after Christmas. I believe a few other friends are to be here also; but I am no longer such a fool about strangers.
Many a time, things which you have said to me, and which then I scarcely heeded, return to my mind. How often, for instance, you have told me that we lose much real enjoyment by that sort of fear or reserve which I used to feel at the sight of a new face; and now that I have learned to listen attentively to conversation, I see what amusement, as well as knowledge, one may gain from the mixture of characters to be met with in society. Indeed, every day shews me how much real goodness there is, though of various kinds, among people who at first sight seem only intent on their own affairs.