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Updated: June 16, 2025
This singular and interesting weed propagates itself on the waves, and there sustains, as on the shore of New Providence, zoöphytes and mollusks which also abound in these latitudes.
Among the Mollusks, Brachiopods are still prominent, one new genus among them, the Productus, being very remarkable on account of the manner in which one valve rises above the other.
It has been estimated that there are about four thousand species or kinds of Protozoans, about twenty-five thousand species of Mollusks, about ten thousand species of birds, about three thousand five hundred species of mammals, and from two hundred thousand to one million species of insects, or from two to five times as many kinds of insects as all other animals combined.
The objection that broad statements of this kind, after all, rest largely on negative evidence is obvious, but it has less force than may at first be supposed; for, as might be expected from the circumstances of the case, we possess more abundant positive evidence regarding Fishes and marine Mollusks than respecting any other forms of animal life; and yet these offer us, through the whole range of geological time, no species ordinarily distinct from those now living; while the far less numerous class of Echinoderms presents three, and the Crustacea two, such orders, though none of these come down later than the Palæozoic age.
One sees in a moment that the Sargassos, of which there are several species on Tropical shores, are a genus of themselves and by themselves; and a certain awe may, if the beholder be at once scientific and poetical, come over him at the first sight of this famous and unique variety thereof, which has lost ages since the habit of growing on rock or sea-bottom, but propagates itself for ever floating; and feeds among its branches a whole family of fish, crabs, cuttlefish, zoophytes, mollusks, which, like the plant which shelters them, are found nowhere else in the world.
I should add, that, beside the Polyps and the Acalephs, Mollusks also have their representatives among the Corals.
The objection that broad statements of this kind, after all, rest largely on negative evidence is obvious, but it has less force than may at first be supposed; for, as might be expected from the circumstances of the case, we possess more abundant positive evidence regarding Fishes and marine Mollusks than respecting any other forms of animal life; and yet these offer us, through the whole range of geological time, no species ordinally distinct from those now living; while the far less numerous class of Echinoderms presents three; and the Crustacea two, such orders, though none of these come down later than the Paleozoic age.
The aquarium must be built up slowly and tentatively, object by object: plants first, and of the simplest kinds; and not until they are well settled, and the water beaded with oxygen bubbles, should we think of introducing living creatures, and even then only the hardier kinds of actinias, mollusks, and crabs.
The crustaceans live within their shells or take advantage of ready-made refuges of limestone, expelling their former owners; the animal-plants exhale toxins; the planctonic beings, transparent and gelatinous, burn like a crystal exposed to fire; some organisms apparently weak and flabby, have in their tails the force of a carpenter's bit, perforating the rock sufficiently to create a cavern of refuge in its hard interior.... And the timid mollusks, trembling and succulent pulp, have fabricated for their protection the strong shields of their valves, two concave walls that on opening form their door, and on closing, their house.
The swimming life gave rise to higher and stronger forms; but did its maintenance give immediate advantage in the struggle for existence? This is an exceedingly interesting and important question, and demands most careful consideration. But we shall be better prepared to answer it in a future lecture. The period of development of mollusks, articulates, and vertebrates, is really one.
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