58 



LEECHES 



pulsatile vesicles so it is perhaps not surprising that its rate of 

 metabolism is high. In the two Erpohdella species as well as in 

 Piscicola the oxygen uptake was proportional to the oxygen 

 concentration of the water, suggesting that low oxygen concentra- 

 tions produced no special physiological response from the animals. 

 The curves for Glossiphonia complanata and Helohdella stagnalis 

 on the other hand are comparatively level over part of the range 

 of oxygen concentration, suggesting that there is some regulation 

 of oxygen uptake by the leeches. 



Fig. 29a. Apparatus used in leech respiration studies, giving 

 the results illustrated in Fig. 32. The leeches were placed in 

 the chamber C and subjected to a constant stream of water 

 from reservoir A, driven by pressure from a gas or air cylinder. 

 The oxygen content of the outflow was determined by a drop- 

 ping mercury electrode in chamber F. From Mann, 1958. 



The experiments described above were all repeated with leeches 

 which were allowed to become acclimatized overnight to the 

 oxygen concentration of the experiment. Only one leech responded 

 to this treatment, Erpohdella testacea, which began to regulate its 

 oxygen uptake at concentrations above J air-saturation (Fig. 30). 

 Further investigations showed that such acclimatization occurs in 

 summer but not in winter. This leech lives in ponds which are 

 relatively anaerobic in summer and the adaptive significance of 

 such a mechanism is clear. When the actual method of adaptation 

 was studied it was estabHshed that the leech did not make ventila- 

 tory movements so presumably it increased its rate of circulation. 



