CHAPTER XVIII 

 LEECHES 



The annelids as a group are not of such primary importance 

 as parasites as are the two other great groups of " worms." 

 In fact only one class, the Hirudinea or leeches, contain species 

 which are parasitic on the higher animals. 



No boy who has ever experienced the unbounded delights of 

 hanging his clothes on a bush and immersing his naked body 

 for a swim in a muddy-bottomed river or pond is unfamiliar 

 with leeches or " bloodsuckers." Still more familiar with them 

 is any tourist who has journeyed on foot through the jungles of 

 Ceylon or Sumatra, or any explorer who has walked through 

 the warm moist valleys of the Himalayas or Andes, and who has 

 been attacked by hordes of bloodthirsty land-leeches which in- 

 fest these places. Nor is it hkely that the thirsty traveler in 

 North Africa or Palestine who stops to gulp a few mouthfuls of 

 water from a pool or stream and who accidentally inbibes one of 

 the leeches which infest such waters will not always remember 

 the bleeding and unpleasant sensations, and perhaps dangerous 

 symptoms, which follow the settlement of the leech in the mouth 

 or nasal passages. 



General Anatomy. — The leeches are segmented worms be- 

 longing to the phylum Annelida, in company with earthworms, 

 kelp worms, etc. They are distinguished from other annelids 

 by the absence of any bristle-hke outgrowths from the body 

 (setae) and by the presence of two suckers, one at the mouth for 

 sucking food, and a large one at the posterior end for adhering 

 to surfaces. The rings of the body as seen on the surface do not 

 correspond to true segments of the body as they do in other 

 annelids; there are several rings to most of the segments. The 

 bodies of leeches are extremely elastic, and can be stretched at 

 will to several times the contracted length. In fact the usual 

 method of locomotion, other than an undulating mode of swim- 

 ming, is by alternately expanding and contracting the body, 



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