HABITS OF LEECHES. 213 



Class DISCOPHORA or HIRUDINEA. Leeches. 



This class includes forms in which the body is elongated 

 or flattened, devoid of appendages or bristles, and marked 

 externally by rings, which are much more numerous than the 

 segments as displayed in the internal structure. The body 

 cavity is much reduced and communicates with the well- 

 developed vascular system. The nephridia are numerous and 

 segmentally arranged. There is always a posterior sucker, and 

 the mouth is frequently suctorial also. Almost all are herma- 

 phrodite, the male organs are numerous and usually segmentally 

 arranged. The nephridia do not function as ducts for the 

 reproductive organs. 



Leeches show several very distinct Annelid characters, 

 but on the other hand differ from ringed worms and agree 

 with flat worms in having suckers, in the absence of bristles, 

 in the frequently flattened form and other features. It is 

 impossible to say how far these resemblances with flat worms 

 are due to the adoption of a peculiar mode of nutrition, but 

 the evidence on the whole seems to be in favour of Annelid 

 affinities. 



Most leeches are worm-like aquatic animals, with blood 

 sucking propensities, but some live in moist soil, and others 

 keep to the open surface, while the parasitic "vampire" 

 habit, familiarly illustrated by the apothecary's ancient 

 panacea, is in many cases replaced by carnivorous habits 

 and predatory life. The medicinal leech (Hirudo) is 

 typical of the majority, for it lives in ponds and marshes, 

 and sucks the blood of snails, fishes, frogs, or of larger 

 available victims. The giant leech (Macrobdella valdiviana\ 

 said to measure 2\ feet in length, is subterranean and 

 carnivorous, while the wiry land leeches (Hcemadipsa, &c.), 

 of Ceylon and other parts of the East move in rapid somer- 

 saults along the ground, fasten on to the legs of man or 

 beast, and gorge themselves with blood. By attaching the 

 head end by the mouth and loosening the tail sucker, then 

 fixing the tail and extending the anterior region, many leeches 

 move very quickly and deftly, while at other times, or in 

 other forms, the mode of locomotion is by graceful serpent- 

 like swimming, or by gentle gliding after the manner of 

 snails. The hungry horse leeches, "whose daughters cry 



