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THE INTELLECTUAL OBSERVER,
BY HENRY J. SLACK, F.G.S., SEC. R.M.S.
(With a Coloured Plate.)
The shores of the Phillippine Islands yield the exquisite object which has been well called Venus' Flower-basket, and which is known to science as a sponge, to which the name Euplectella speciosa has been appropriately given. The ordinary observer, familiar only with the sponges in domestic use, or with somewhat similar structures of branched and finger-like forms frequently found on the beaches of frequented watering-places, will be much surprised at finding the name of sponge applied to the elaborate network of the Euplectella, which looks like an exceedingly delicate fabric of some such material as biscuit china, and which might readily be taken for a coral, although an investigation of its structure would show that it was entirely different from any polyp formation. Our engraving represents one of the finest of the British Museum specimens, but the following description is chiefly taken from a specimen in the writer's possession, which he was able, at no small risk of its destruction, to examine more carefully than could be effected in any public institution.
The naturalist groups together a number of bodies varying considerably in appearance, in structure, and in material, under the designation sponge. Sponges are, however, all alike in certain general characters. They all consist of a living mass of delicate gelatinous fleshy material, called sarcode, and of a framework or skeleton, with certain appendages, which is either horny (keratose), calcareous, or silicious. The common toilet sponge belongs to the horny series, and the Venus' Flower-basket is the most exquisite of the silicious.
Whatever may be the form of the sponge skeleton, or of the spicules of various shapes which belong to it, or are embedded in the soft flesh, it is by, and in, that flesh, that they
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are all produced. In the silicious series, the glossy threads, or spicules, have a very small channel running through them, and they are formed, not in one piece, as a glass-blower spins his so-called hair, but by a series of additions, arranged as concentric layers, each layer being a deposit from the living sarcode.
In the Euplectella the structure bears, at first sight, an aspect of basket-work, and imagination might picture the young mermaidens varying their legendary occupation of combing their sea-green hair, by employing their finny fingers in weaving together the glittering threads of which it is composed. It is, however, not a product of any mechanical plaiting, but of organic life and growth, and a microscopic examination at once distinguishes it from any structure put together by the intertwisting of separate fibres. To view the Euplectella under the microscope without breaking it to pieces requires a good deal of trouble, and a little skill; but it is very advisable to examine it in an uninjured condition, as well as to study details of structure in fragments that may be broken off. From the size of the Fuplectella it cannot be examined if laid across the stage of Ross's large and fine microscope, as that instrument, so admirable in most other particulars, has not enough rack-room to raise a low-power object-glass to the focussing height above so thick an object. Smith and Beck's pattern is superior in this respect, and in our investigation we employed both. To view the Euplectella under the Ross binocular, we rigged up a temporary stage of card under the brass stage of the instrument, and then got on pretty well with three inch, and one and a half inch powers. Further examination was made with a monocular Smith and Beck, the delicate sponge being placed across the stage, and supported by a box at each end.
A good specimen, fully grown, of the Venus' Flower-basket will be rather more than a foct long, and about two inches in diameter at its widest end. It takes, as our plate shows, the curve, and somewhat the form, of a cornucopia. At the base it is covered with a quantity of silicious hairs, part of which the natives have a knack of removing before sending it to Europe. The natural position of this sponge is upright, and it probably grows on a soft sea-bed. At nearly equal distances, say from one-eighth to three-sixteenths of an inch apart, vertical bundles of silicious threads rise from the base, and are continued to the top of the structure, and at right angles to these we observe a series of horizontal rows, crossing the former and giving rise to square meshes of considerable regularity. Slanting fibres cross the corners of these squares, and give a more or less rounded appearance to the central apertures;