CIRCULATION AND RESPIRATION 



59 



Erpobdella festacea 



x>^ Erpobdella octoculafo 



X 



Oxygen concentration, ml/L 



Fig. 30. The relation between oxygen consumption and 



oxygen concentration in the two species of Erpobdella after 



acclimatization overnight to the concentration of oxygen at 



which the readings were taken. From Mann, 1956. 



The low oxygen concentrations must have stimulated the adrener- 

 gic mechanism, thus accelerating the rate of contraction of the 

 lateral sinuses. 



It is of interest to enquire into the function of haemoglobin in 

 leeches, for in many annelids such as Arenicola it is of value only 

 under conditions of extremely low oxygen concentrations in the 

 surrounding water. In Liimhricus it seems likely that the haemo- 

 globin transports between one-quarter and one-half of the oxygen 

 used by the worms. Johnson (1942) compared the oxygen con- 

 sumption of Lumhricus herculeus at various concentrations of 

 atmospheric oxygen, before and after the inactivation of the 

 haemoglobin with carbon monoxide, care being taken to ensure 

 that the respiratory enzymes were not affected. She concluded 

 that the haemoglobin of the blood was responsible for carrying 

 about 23% of the respired oxygen when the oxygen pressure was 



