The medicinal leech is a leech used in bloodletting. It lives in fresh water, and is common in Germany, Bohemia, and Russia. Its diet consists of the blood of vertebrates, to which the leech attaches itself by its suckers. Of these, one is posterior and imperforate, the other anterior, with the mouth in the center. Within the mouth lie three triangular tooth-plates, by means of which a small triradiate incision is made in the skin of the animal attacked. This done, the leech proceeds to fill its crop, which extends almost from end to end of the body, and has eleven lateral pockets. When these have become distended with blood, the leech drops from its temporary host, and the slow process of digestion begins. Leeches usually move by attaching alternately the anterior and posterior suckers, somewhat after the fashion of a 'looping caterpillar', but they can also swim by movements of the whole body. The eggs are laid in cocoons in damp earth.
John H. Finley ed. Nelson's Perpetual Loose-Leaf Encyclopaedia (vol. 7) (New York, NY: Thomas Nelson and Sons, 1917) 260