92 



THE PHYSIOLOGY OF EARTHWORMS 



of active movement should be a low respiratory period, and vice 

 versa, particularly when such periods last for hours rather than a 

 few minutes. 



Ejfect of Variations in Oxygen Availability 



When earthworms are living in normal air conditions, as when 

 feeding on the surface of the ground, respiration progresses at an 

 average rate of 38-7-45 -2 mm^/g/hr. The partial pressure of oxygen 

 is approximately 152 mm Hg in normal atmospheric air. Earth- 

 worms, however, spend long periods underground in burrow 

 systems which may be deep, down to 6 feet, and narrow. It is 

 conceivable, but unlikely, that the air in these channels becomes 

 depleted of oxygen as it is utilized by the inhabitant of the burrow, 



Table 13 



Rate of Respiration of Lumhricus terrestris as a Function of 



THE Partial Pressure of Oxygen in the Atmosphere 



(From Johnson, 1942) 



O2 p.p. 

 mm Hg. 



Rate 



mm^/g/hr 



152 



38-7- 

 45-2 



76 



35-2- 

 42.5 



38 



23-3- 

 25-0 



19 



15-4- 

 16-7 



6-7- 



7-2 



but oxygen tensions may fall considerably without the activity of 

 worms (Russell, 1950). Laboratory experiments have indicated that 

 oxygen tensions must be quite drastically lowered to aifect the 

 rate of respiration of earthworms. A decrease of 50% in the partial 

 pressure of oxygen (76 mm Hg) does not alter oxygen consumption 

 rates but a reduction to 25% (38 mm Hg) depresses respiration 

 by 55-60%, and conditions of greater oxygen lack decrease the 

 rate further still (Table 13) (Johnson, 1942). 



The partial pressure of oxygen also affects the respiratory rate of 

 Lumhricus when immersed in water as mentioned previously (p. 

 87). The fresh- water oligochaete Tiihifex tubifex, however, appears 

 unaffected by changes in oxygen availability. The worms live in a 

 mud substratum, which may at times become almost devoid of 



