98 



LEECHES 



centre of the cloud of snail juice (Fig. 51). Hemiclepsis reacts to a 

 fish extract in a similar manner but Piscicola which is also a fish 

 parasite shows no such reaction. This is interesting in view of the 

 fact that Hemiclepsis normally lives in still water and Piscicola in 



Fig. 51. Successive positions of three specimens (1, 2 and 3) 

 of Glossiphonia complanata after addition of snail extract to the 

 water (dotted area) at 16.55 hr. Arrows indicate direction of 

 light; times are in hours and minutes. Temperature, 16°C. 

 From Herter, 1936. 



running water or the surf zones of lakes. It is unlikely that in its 

 natural surroundings chemical substances will stay in one place 

 long enough for Piscicola to react to them. 



A detailed study of the substances which evoke a reaction in 

 Hirudo was made by Kaiser (1954). He placed five leeches in 

 200 ml of water in a dish and when they were at rest he added a 

 test substance drop by drop. With acids the leeches responded 

 by making characteristic jerking and quivering movements, while 



