Page:Popular Science Monthly Volume 17.djvu/494

478 may be better rewarded for their toil and their sagacity than was the Babylonian philosopher; for perhaps, by that time, the magi also may be reckoned among the members of a forgotten fauna, extinguished in the struggle for existence against their great rival common sense.—Nineteenth Century.

 

ANY swamps and ponds, which are now considered utterly worthless, might be made sources of great profit by devoting them to the production of a worm which is exceedingly valuable, and the cultivation of which requires no expensive outlay. This worm is the medicinal leech; formerly esteemed of no value, and hated and hunted on account of its bloodthirstiness, it has commanded extremely high prices since its useful qualities have been recognized. Its general appearance is familiar, its internal structure is very wonderful. Its body forms a cylindrical sac, composed of a course of about one hundred rings. The terminal ring of the hinder part is broader and stouter than the others, and serves as a foot. At the front extremity, which is more pointed than the hinder part, are two fine, separated lips, which, when brought together, form a closed ring. Several straight lines run along the back for the whole length of the body, while the belly is of a clearer color and is mottled with irregular dark spots. The body of the leech is so elastic that it can stretch itself out to a length of nearly ten inches, and draw itself up again to within the dimensions of an olive. Within and back of the lips are three thick membranous pads covered with a thin, horny mass bearing several rows of microscopic teeth; they may be described as the jaws. Between the jaws passes the very narrow throat, which can be opened and closed at will by means of a transverse muscle. The animal derives its importance to man from the close aggregation of the movable lips, the narrow throat, and the toothed jaws, for it is enabled by this peculiarity to break through the skin and suck the blood from it. The mechanical operation is as follows: When the lips close in a circle upon the air-tight skin, the jaws are also brought down to it and their saw-like teeth are pressed tight upon the cuticle. The throat having now become fast closed, the head of the worm is drawn back a little, and the lips are thereby given the form of an exhausted cupping-glass, which is divided internally, by the jaws still fastened to the skin, into three distinctly separated parts. The skin is powerfully sucked up into these three divisions of the cupping apparatus till it is torn, and rents are formed corresponding to the three spaces between the jaws, the inner ends of which run into each other and form a larger,