Page:Popular Science Monthly Volume 6.djvu/26

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16
THE POPULAR SCIENCE MONTHLY.

its proper place the invisible cement. The precise method of the operation is not, I think, understood. It seems to me that the process is not a direct one, but rather the result of another process. All can recollect the once-popular mackintosh, a sort of water-proof cloak. It was little else than ordinary cloth, with an insoluble substance infused into the spaces between the fibres of the fabric. Is it not likely that the oyster has a process of its own not very dissimilar?—that it deposits a delicate net-work of animal substance as the staple, and that this is soon filled in with carbonate of lime, taken in mechanically from the salt-water? And this same organ has, along its edge, a series of pigment-cells, from which it exudes the paint that decorates the shell. In this respect the American oyster is a very plain affair. That of Europe has more color on the shell, I think, as it is more corrugated in form, and of less size. Our own oysters, we believe, both in quality and size, excel all others. (For a group of European oysters, of ages varying from that of three days to that of one year, see Fig. 2.)

If the shell of an adult oyster be examined, it will appear to be a series of shells, lying or lapping upon each other like tiles. There is, however, a difference. The lap of the upper one is not merely on the upper end of the lower one, but also on the middle, thus leaving a margin nearly all round. So the uppermost layer is always the smallest, and the lowermost one is always the largest of the series. The oystermen call these laps "shoots"—each one represents a season's growth. Thus each "shoot" shows the precise size of the oyster at a given year of its life, while the sum of the entire series gives the exact number of years the creature has lived. This shows how often the logic of Nature runs in parallel lines; for it brings up the old maxim again, "Every one to his own trade." The botanist counts the season-rings in the bole of a tree. The jockey tells the age of the horse by its teeth. The drover sets down the age of the cattle he buys by counting the rings on the horns; and in like manner the oysterman comes to a judgment by the number of "shoots" on the bivalve's shell. But all these specialists alike err when giving judgment upon an individual that has reached extreme old age.

The capability of the univalve mollusks to repair the shell when broken has been long known and understood by naturalists. In respect to the bivalves not so much is known. The oyster has some wonderful things in the way of repairing its house after being broken into. A case is known to us in which an oyster was so badly fractured at the nib that a piece of shell about an inch wide was broken off, and the poor animal protruded. An oysterman, for experiment's sake, restored it to the water, and, to be sure, put it close by a pole driven into the bed. This was in the spring. In September it was taken up and examined, when lo! the ingenious little builder had thoroughly repaired all damages!

The Nervous System of an Oyster.—Physically unstrung, the