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THE POPULAR SCIENCE MONTHLY.

effort that carries belief to an opposite extreme—changing approval into a disapproval that is entire instead of partial. Hence, in the one case, as in the other, we must infer that the resulting obstacle to well-balanced conclusions can become less only as social evolution becomes greater.

 

THE BORERS OF THE SEA.

MANY stories are current as to how inventors have borrowed or stolen their ideas from Nature, and there has been much ingenious discussion as to whether hints thus appropriated are properly patentable. Boring is an example of natural processes that have been thus used by art, and it is remarkable that the lowest creatures are the most skilful mechanics in this particular. An eminent living inventor, who has made a fortune out of a patent auger, hit upon the method followed by the most successful insects which bore into hard wood. And so we are assured that the celebrated engineer Brunei, in constructing the Thames Tunnel, but imitated the shell-lined burrow of the Teredo navalis, or Ship-worm. This mollusk in shape resembles a worm, and surrounds itself with a shell open at both ends. From the mouth it can protrude its short foot, and the other extremity of its body; the "tail" is bifurcated, one prong being the inspirator and the other the expirator tube of the siphon which constitutes the animal's nutritive apparatus.

It has long been a subject of controversy among naturalists how the Ship-worm and other mollusks of the same family bore their way into the rocks and timbers which they penetrate. As regards the Pholades, for instance, Mr. Robertson, who kept these animals alive in their chalky burrows, and studied their habits with the closest attention, found that when burrowing they make a half-revolution of their shell to the right, and then back to the left, after the manner of a carpenter using a brad-awl. The Pholas is a bivalve, club-shaped, and the outer surface of its shell is covered with small teeth in curves, and resembling the face of a rasp. These teeth would naturally seem well suited for the purpose of boring, yet all naturalists are not agreed on this point. Thus, some hold that the animal secretes an acid solvent, which causes the material in which it is burrowing to decay. Then only is it that, securing itself with its sucker-like foot, it works itself from right to left, and vice versa, to widen the passage. But Mr. Gwynn Jeffreys, as stated in the December number of The Popular Science Monthly, is of opinion that the foot, which he says is charged with siliceous particles, is the true boring apparatus of all the conchifera, and acts like the leaden wheel of the lapidary.

The history of the development of the Teredo is thus given by M.