Leeches 175 



Leeches — The leeches constitute a small group whose 

 members are nearly all found in fresh -water. They 

 occur under stones and logs, in water- weeds or bottom 

 mud, or attached to larger animals. The body is 

 always depressed, and narrowed toward the ends, more 

 abruptly toward the posterior end where a strong sucker 

 is developed. The front end is more tapering and neck- 

 like, and very pliant. There is no distinct head, but 

 at the front is a sort of cerebral nerve ring and there are 

 rudimentary eyes in pairs, and surrounding the m.outh 

 is a more or less well-developed anterior sucker. The 

 great pliancy of the muscular body, the presence of the 

 two terminal suckers, and the absence of legs or other 

 appendages determine the leech's mode of locomotion. 

 It ordinarily crawls about by a series of loopings like a 

 ''measuring worm," using the suckers like legs for 

 attachment. The more elongate leeches swim readily 

 with gentle undulations of the ribbon-like body. The 

 shorter broader forms hold more constantly with the 

 rear sucker to some solid support, and when detached 

 tend to curl up ventrally like an armadillo. 



Leeches range in size from little pale species half an 

 inch long when grown, to the huge blackish members 

 of the horse-leech group {Hcemopis) a foot or more in 

 length. Many of them are beautifully colored with 

 soft green and yellow tints. The much branched 

 alimentary canal, when filled with food, shows through 

 the skin of the more transparent species in a pattern 

 that is highly decorative. 



Leeches eat mainly animal food. They are para- 

 sites on large animals or foragers on small animals or 

 scavengers on dead animals. Very commonly one finds 

 the parasites attached to the thinner portions of the 

 skins of turtles, frogs, fishes and craw-fishes. There is 

 no group in which the boundary between predatory and 

 parasitic habits is less distinct than in this one; many 



