Page:Popular Science Monthly Volume 17.djvu/495

Rh still three-parted wound. It follows that the sucking of the leech must be without effect on the hairy parts of the body, where a cupping-glass could not be made air-tight, and this is the case. When the space between the skin and lips, which answers to the interior of the cupping-glass, is filled with blood, the throat is opened, the blood is drawn

 (Hirudo medicinalis) seen from above. 2. The same, under side; a b, sexual organs. 3. The nervous cord with its ramifications: a, forward upper part; b, forward lower part; c, posterior nervous node.

by sucking movements of the body into the maw, and the mouth of the worm is filled anew with blood. The long, narrow maw is competent, by means of twenty-six peculiarly formed sacs or valves, which are arranged in two rows, to retain an immense quantity of blood without any of it being driven back by the muscular activity of the body; and, if a hole is pricked in the body of the leech at the rear end of the maw, all the blood that has been sucked up may be made to flow out. On account of the narrowness of its throat, the leech can not take solid food. Its usual nourishment consists of animal and vegetable infusoria,