94 



THE PHYSIOLOGY OF EARTHWORMS 



surface area for gaseous exchange to take place. At the same time 

 rhythmic corkscrew movements agitate the water surrounding the 

 worms and stimulate currents of water from above containing more 

 oxygen to flow down around the animals. These movements are 

 inversely proportional to the oxygen supply below the water 

 surface (Alsterberg, 1922, Dausend, 1931). Dobson and Satchell 

 (1956) also have interesting speculations on the availability of 

 oxygen with regard to bodily proportions in the earthworm 

 Eophila ociilata. Prolonged exposure to low oxygen tensions does 



0-5 



0-4 



a. 0-3 



e 



0-2 



O 0- 



Oxygen , 



4 



mL/hr 



Fig. 28. Oxygen consumption of Tuhifex as a function of oxygen 

 tension of surrounding water (from Dausend, 1931). 



not, however, lead to an increase in the amounts of haemoglobin 

 present. 



The respiratory rate of 2\ tubifex is virtually constant at all 

 oxygen tensions above 0-5% O2, at which concentration the uptake 

 is 0-6 mm^/g/hr at 19 °C. If the oxygen tension falls further the 

 respiratory uptake falls, slowly at first, to 04 mm^/g/hr at 0-1% 

 oxygen, and then decreasing rapidly as the oxygen available 

 approaches % (Fig. 28) . The haemoglobin of the blood is responsible 

 for only a fixed fraction of the respiratory exchange since carbon 



