254 



GENERAL ZOOLOGY 



The digestive system of a leech secretes substances that 

 prevent the blood used as food from clotting. This is in- 

 teresting because after a leech is filled with blood it has 

 enough food to last it for several months. When gorged 



with blood a leech is relatively inac- 

 tive, staying in some secluded place 

 until ready to seek new prey. 



Leeches of a different genus 

 (Pisci'cola) frequently become 

 parasitic on fishes. The horseleech 

 (Hsemop'is marmora'tis) lives only 

 part of the time in water and 

 spends much time burrowing in 

 the soil. This species is largely 

 a scavenger, though it also feeds 

 snails, earthworms, and other 

 small animals, and 

 frequently becomes a 

 bloodsucker. Some 

 species in the tropical 

 countries live on land 

 permanently and are a 

 great nuisance to pe- 

 destrians in the forests. 

 There are two differ- 

 ent kinds of wounds 

 made by leeches. Some 

 leeches have three saw-like jaws which cut a Y-shaped open- 

 ing in the skin. The jawless leeches have a conical lancing 

 organ in the pharynx with which they pierce the skin. 



Bloodsuckers feed upon human blood of bathers in 

 fresh-water streams and lakes of many regions. In the not 

 very distant past leeches were commonly used by physi- 

 cians as a relief from many diseases. Blood-letting was then 



Fig. 133. Leech. (Slightly reduced) 



