ANNELIDS IN GENERAL 



245 



284. Hirudinea. — The class Hiriulinea contains the leeches, which 

 differ from other annelids in that they possess two suckers, one inclosing 

 the mouth and the other being ventral to the anal opening. They also 

 have a smaller number of metameres than in other annelids. There 

 appears to be a greater number of these, however, than really exist, 

 because each one is marked by several transverse grooves (Fig. 147). 



/4nfer/or 

 sucker 



Jaws 

 Mouth 



Opening oF 

 vois deferens 



Opening of 

 o\/i<pluct — 



A/ephrip/io 

 pore 



Sense 

 papillae 



XXTTT 

 VXIV 



XXVt 



Anus 



Pes ferior 

 sucker' 



Fig. 147. — The medicinal leech, Hirudo medicinalis Linnaeus. (From Borradaile, 

 " Manual of Elementary Zoology," by the courtesy of Oxford University Press.) A, the whole 

 animal, ventral surface. The segments are shown by roman numerals. B, the anterior 

 end, dorsal surface. C, the posterior end, dorsal surface. A, natural size; B and C slightly 

 enlarged. 



The suckers are used as organs of attachment when the animal is at 

 rest and also as organs of locomotion when the animal moves about upon 

 a firm substratum, the movement being similar to that of a measuring 

 worm. Leeches are able to swim freely through the water, the body 

 performing vertical undulations. 



The mouths of some leeches, such as the medicinal leech (Fig. 147), 

 are provided with jaws armed with chitinous teeth. When such a leech 



