THE AMERICAN MEDICINAL LEECH. 833 



minute tentacles at the end; the body is long, smooth, and tapers gradually to both ends, and 

 the muscular system is very powerful, and so arranged as to enable these Worms to coil them- 

 selves up into the shape of an open spiral, like a corkscrew, and then to rapidly rotate themselves 

 on the axis of the spiral. When the sharp head is inserted into the loose mud or sand and the 

 body is thus rotated, it penetrates with great rapidity and disappears almost instantly. Both 

 these species are found on sandy as well as on muddy shores and flats near low-water mark, and 

 also in deeper water. The one usually most abundant is R. dibranchiatus'. This is readily distin- 

 guished by having a simple gill both on the upper and lower sides of the lateral appendages. 

 The other, R, americanux, has gills that are more or less branched on the upper side of the 

 appendages, but none on the lower side ; the appendages are also longer, especially posteriorly, 

 and differently shaped. The proboscis is remarkably long and large, and when fully protruded it 

 shows four large, black, sharp, fang-like jaws or hooks. Both these Worms are destitute of true 

 bloodvessels, such as most of the allied Worms possess, but have the general cavity of the body 

 tilled, between the various organs, with bright red blood, which shows through the skin, giving a 

 more or less red or purple color to the whole body and proboscis." 



The principal species of marine Worms which are used as bait are the Nereis virens, Nereis 

 Timliuta, Diopatra cuprea, Arenicola marina, Clymenella torquata, Marphysa sanguined, Arabella 

 opal ina, and Rhynchobolus dibranchiatus. 



The Earth Worm might also be mentioned in this connection, as it is likewise very commonly 

 used as a fish-bait, especially in fresh waters. All sportsmen, from boyhood up, are acquainted 

 with this simple form of bait, which is more easily obtained than any other. Large quantities are 

 used annually, but no statistics can ever exist to determine the amount, which is irregularly 

 distributed over the country. 



234. THE LEECHES. 

 THE AMERICAN MEDICINAL LEECH MACROBDELLA DECORA, Verrill. 



Structure of Leeches. In the true Leeches, which belong to the order Hirudinea, the body is 

 flattened, divided into numerous short and indistinctly marked segments, and bears neither bristles 

 nor appendages of any kind. The head is small, with five pairs of minute, simple eyes, and each 

 end of the body terminates in a sucker. " The mouth is armed internally with three pharyngeal 

 teeth arranged in a triradial manner, so that the wound made in the flesh of persons to whom the 

 Leech is applied consists of three short, deep gashes radiating from a common center." The 

 stomach is large, and the nervous system consists of a "brain" and ventral cord. The Leech is 

 hermaphroditic. The eggs, which range from six to fifteen in number, are contained in a sort of 

 spongy, slimy cocoon, from half an inch to an inch in diameter. These are deposited near the 

 water's edge and hatched by the heat of the sun. Eespiration in the Leeches is carried on through 

 small apertures arranged along the under surface of the body. The Leech swims with a vertical 

 undulatory motion and moves both in and out of the water by means of its suckers, fastening itself 

 first by one and then by the other, and alternately stretching out and contracting its body. 



There are two or three species of Leeches, known as medicinal Leeches, which afford the 

 most convenient means of drawing blood from the human body. They have been used l>y 

 physicians for this purpose for many years, and have given rise to a very extensive and profitable 

 trade. One of the species belongs to North America. 



Distribution and structure of the American Leech. Although numerous species of Leeches 

 abound in the fresh waters of the United States and are related to the fisheries in various ways, 

 r>3 F ' 



