Page:The American Cyclopædia (1879) Volume X.djvu/316

 310 LEECH tory in 1857, and Archbishop King lecturer in divinity in 1863 ; and is now (1874) arch- deacon of Dublin. He has published a num- ber of works, among which are the Donellan lectures for 1852, " Inspiration of Holy Scrip- ture, its Nature and Proof" (1852; 4th ed., 1865); "Three Introductory Lectures on Church History" (1858); "Progress of As- tronomy" (1860); "Translations in English Verse of Ovid, Horace," &c. (1860); and "Re- cent Forms of Unbelief" (1864). LEECH, a red-blooded, footless, smooth- bodied, abranchiate annelid of the family hiru- dinei, and genus sanguisuga (Sav.) or Mrudo (Linn.). The body is soft, retractile, composed of numerous segments, with a sucker at the posterior extremity, serving both to attach and to move the animal. The muscular system is well developed, closely embracing the viscera ; the sucker has both circular and radiating fibres. The nervous system consists of a large anterior cerebral ganglion, and a chain of ventral gan- glia connected by two contiguous cords ; the ganglia are fewer than the segments, the first and last being the largest, the former sending filaments to the lips, and the latter to ttte suck- er ; there is also a splanchnic system of small anterior ganglia which send filaments to the parts about the mouth and to the intestinal ca- nal. The sense of touch is particularly devel- oped at the anterior extremity. There are ten eye specks symmetrically arranged upon the neck, each a transparent cylindrical body bulg- ing out under the skin like a cornea, enveloped in a layer of black pigment, receiving a filament from the cephalic ganglion, according to Wag- ner having a lens and a vitreous body (though this is denied by others), and constituting light-perceiving if not light-refracting organs. The flattened body tapers toward each end, the mouth being at the anterior extremity and pro- vided with a sucking apparatus; at the base of the pharynx are. three fleshy swellings, the projecting border of which is edged with bicus- pid teeth, causing wounds shaped like a three- rayed star. The intestinal canal is straight, but deeply constricted in many places, each such portion sending off short ca3ca on each side ; the anal opening is on the back directly above the posterior sucker. There are salivary glands around the commencement of the intestine, and a glandular hepatic organ envelops a great part of this canal. The blood contains colorless granulated globules; there is a central con- tractile vessel, and a circulation and oscillation in longitudinal and lateral vessels. Respiration is effected by means of 17 pairs of internal branchiaa or aquiferous canals without ciliated epithelium, opening upon the ventral surface of the body, and surrounded by a network of blood vessels. Reproduction is effected by sex- ual organs, and the two sexes are united in the same individual, they being true hermaphro- dites ; the eggs, from 6 to 15, are contained in a cocoon, surrounded by a thick spongy sub- stance said to be ejected from the mouth, de- posited near the edge of the water, and hatch- ed by the heat of the sun ; the young leave the egg without undergoing any metamorphosis. The leech inhabits the water principally, and swims with a vertical undulating motion ; out of the water it moves by the disks or suckers, fastening itself first by one and then by the other, alternately stretching and contracting the body ; it is torpid in winter, hiding in the mud ; it can live a long time in sphagnous moss or in moist earth, and can thus be transported for long distances. Leeches live at the expense of other animals, whose blood they suck ; they attach themselves to fishes, batrachians, inver- tebrates, and to mammals and men that venture into the fresh water inhabited by them. Many species are used for medical purposes, of which the most common are the gray and the green leeches of Europe (S. medicinalis and offici- nalis, Sav.),' generally considered varieties of one species ; both have six longitudinal f erru- Leech (Sanguisuga medicinalis). 1. Leech. 2. Anterior extremity magnified. 8. Jaw detached, magnified. 4. Part of belly magnified. ginous stripes on the back, the four lateral ones interrupted by black spots ; the back varies from blackish to grayish green ; the under parts in the first variety are greenish with black spots and edgings, in the second yellowish green without spots; the length varies from 2 to 4 in. They formerly inhabited in great numbers the marshes and streams of most countries of Eu- rope ; but of late years the demand for medical purposes has exhausted most of the localities in central and southern Europe ; the Swedish leeches are now generally considered the best. There are many American species, of which the Mrudo decora (Sav.) is extensively used in the interior of the middle states ; the color is deep greenish above with three rows of square spots, the central brownish orange, and the lateral black ; the under parts are spotted with black ; it varies in length from 3 to 5 in. ; it is especially abundant in Pennsylvania, and several hundred thousand are employed annu-