1 88 TJic h'ish NahiraHst. [August, 



THE IRISH FRESHWATER LEECHES. 



BY R. F. SCHARFF, PH.D. 



Eeeches are closely allied to earthworms, but they are 

 readily distinguished from the latter by their oval contour 

 and flattened shape, and by the possession of two suckers, 

 one at each end of the body. There are also anatomical 

 differences which I need not dwell upon, as b}^ the characters 

 mentioned, all the Irish leeches can be at once identified as 

 such. 



Not all the Irish leeches inhabit fresh water ; some live in 

 the sea, and to these I may, perhaps, refer on another 

 occasion. The Common Horse-leech is frequently found 

 under stones in damp situations, occasionally^ far removed 

 from a pond or stream. It might, therefore, be looked upon 

 as a land-leech, however, its usual habitat is the w^ater, and 

 it will never move to a place which does not provide it with 

 a more or less constant supply of moisture necessary'- for its 

 comfort. Real land-leeches exist, but these are mostly con- 

 fined to the tropics, and are fortunately absent from Ireland. 



The word " leech " not being now used to denote a medical 

 man, at once suggests to the popular mind a ferocious blood- 

 sucking animal. Only the Medicinal Eeech, however, is 

 capable of piercing the human skin, whilst the Horse- 

 leech, which is so commonly met with in Ireland, is perfectly 

 harmless. The Irish freshw^ater leeches may be conveniently 

 divided into two groups, viz., Rhyrichobdcllce and Giiath- 

 obdellce. The first of these include the smaller leeches which 

 are unprovided with jaws and possess an exsertile snout or 

 proboscis. Their blood is colourless. All the snail-leeches 

 belong to this group, so-called because they suck the blood 

 of water-snails and other aquatic animals. Though un- 

 provided with jaws, the muscular proboscis can be pushed 

 through the tissues of the victim and the nourishing juices 

 pumped out. 



All leeches with red blood and without a proboscis belong 

 to the other group the Gnathobdella:. As a rule these possess 

 jaws — all the Irish species at any rate do but in England 

 a gnathobdellous leech exists, viz., Trocheta viridis, in which 



