Observations on the structure and nature of flustrae / by R. E. Grant.

Date:
[1827]
Catalogue details

Licence: Public Domain Mark

Credit: Observations on the structure and nature of flustrae / by R. E. Grant. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    part of a line in length, of equal thickness throughout, round at their free extremities, and dissolve with effervescence in diluted nitric acid. They are not perceptible without the aid of a microscope. The spicula are arranged along the whole of each side of the cell; they are placed in nearly parallel groups, of three or four, at short distances from each other, and are ihost numerous at the middle of the cell where the principal part of the polypus is usually coiled up in a spiral turn. In the newly formed cells at the extremities of the branches, we at first ob- serve the spicula only at the part of the cell where the body of the young po- lypus is still entirely shut up in a sac. The cell is usually shut, or nearly shut, at the top, in the retracted state of the polypus, but opens by a kind of semilunar valve, with firm margins, when the polypus is advancing out from the aperture. The back of the cell is formed by a transparent tough membrane, which contains some opaque spots of calcareous matter, and exhibits numerous transparent branched lines, like vessels or fibres, running chiefly in a longi- tudinal direction. When the polypus is dead, and nearly absorbed, many of these vessels are seen radiating from the last remains of the polypus, which appear as a small red or brown spot in the centre of the posterior wall of the cell. The lateral walls of the cell appear to consist of a thin calcareous lami- na, lying perpendicularly to the general plane of the cells, it is white, and very tough; and, when highly magnified, it exhibits fibres or vessels, running lon- gitudinally on its surface. Mr Ellis supposed the lateral walls of the cells of Flustrce to be formed by a tube. When we look perpendicularly on this part, it appears as a white filament; but when viewed laterally, we observe it to consist of a regular thin plate, surrounding the whole margin of the cell. By examining carefully with the microscope the margins and corners of the oells, we observe, that there is a thin transparent membranous lining within the walls of the cell. In the young cells, this internal lining forms a small shut sac at the bottom of the cell, in which the infant polypus is inclosed and matured: this sac gradually extends to the aperture of the cell through which the polypus at length protrudes its tentacula ; and, at last, it is found nearly applied to the walls of the cell. The particles of sand and other matter, which sometimes appear to be within the cells, are generally on the outside, adher- ing to the posterior wall. The polypus of the F. carbasea is nearly twice as long as the cell which con- tains it, and when retracted within the cell, it is found coiled up in a spiral turn, extending from the aperture to the base of the cell. The polypus con- sists of the tentacula, the head, the body, and a large globular appendix, at- tached to the posterior part of the body. The tentacula are usually twenty- two in number, sometimes we observe only twenty-one ; they are long, slen- der, cylindrical, of equal thickness throughout, and have each a single row of cilia;, extending along both the lateral margins from their base to their free extremity. The tentacula are nearly a third of the length of the body of the polypus, and there appear to be about 50 cilise on each side of a tentaculum, making 2200 cilise on each polypus. In this species there are more than 18 cells in a square line, or 1800 in a square inch of surface, and the branches of an ordinary specimen present about 10 square inches of surface; So that a com- mon specimen of the F. carbasea presents more than 18,000 polypi, 3<)fi,ftop