160 MEDICAL ZOOLOGY. 



tinuous. The margins are of an olive color both on the back and belly. 

 This species closely resembles the above, and is found in the same localities. 



H. decora (American leech), Say. 



Body livid, with a dorsal series of twenty-two small red dots, and a lateral 

 series of the same number of black dots of a similar size ; a transverse line 

 of ocular points in -close order before ; on each side of which, and at a short 

 distance from them and from each other, are two points of the same kind ; 

 hence the fulvous with a few black spots. 



Anatomy. The jaws of the leech are three in number, placed longitudin- 

 ally : one superior and median, two others inferior or lateral. Each jaw is 

 semicircular, thin, smooth, and moderately strong. The free convex surface 

 is furnished with forty-six to eighty-three teeth-like chevron-shaped processes, 

 arranged parallel to each other and placed across the cutting edge of the 

 jaw, having the angle turned toward the axis of the mouth. (Moquin- 

 Tandon.) The ventral ganglia of the nervous system are much fewer than 

 the segments of the body, and are bound together by two contiguous cords. 

 The first and last of these ganglia are remarkable for their size. The first 

 sends filaments to the lips, the second to the caudal sucker. Each eye-speck 

 composed of a transparent cylindrical body, a little attenuated and rounded 

 at its inferior extremity, while the opposite one causes the skin to bulge out 

 like a cornea. Its remaining portion is enveloped with a layer of black pig- 

 ment. The intestinal canal varies very much, especially as to the number 

 and volume of its appended caeca. Its very narrow anal opening is upon 

 the back above the pedal sucker. The blood-vessel system resembles in plan 

 that of other Annelida. Beside two median vessels, there are distinguished 

 two lateral ones, which intercommunicate by very numerous transverse ves- 

 sels. From the contractions of these vessels, the blood is driven sometimes 

 forward and sometimes backward, and oscillates from side to side through 

 the transverse canals. With the Hirudinea the two sexes are always united 

 in the same individual. The sexual organs consist of testicles, vasa defer- 

 entia, and vesiculae seminales ; then ovaries, oviducts, and the male and 

 female copulatory organs. The latter are upon the ventral surface of the 

 anterior part of the body and behind the male organs, so that two individuals, 

 by placing together their anterior ventral surfaces in an inverse position, can 

 be mutually impregnated. 



