96 THE PHYSIOLOGY OF EARTHWORMS 



that this product does not alter respiration greatly. Intense activity 

 or prolonged incarceration within the burrow may cause a build up 

 of carbon dioxide in the atmosphere. Shiraishi (1954) placed E. 

 foetida in an artificial burrow and found that when CO 2 is passed 

 over the animal no effect is noted upon its movement until a 

 concentration of 25 % is reached. Any further increase leads to the 

 withdrawal from the area of high concentration. It is possible that 

 such high concentrations may occur, though Russell (1950) says 

 that the maximum concentration of CO 2 obtained in soil is only 

 7%, particularly so after heavy rain has occluded the orifices of the 

 burrow and the well-known migration on the surface of the ground of 

 some species after rain may be ascribable to this reaction. It has 

 also been suggested, however, that this movement is due to lack of 

 oxygen and no conclusion can yet be reached (Ledebur, 1939). 

 Svendsen (1957) suggests that this may simply be a normal dis- 

 persal mechanism. 



In the case of T. tiihifex excess carbon dioxide does not accelerate 

 the waving movements in response to lack of oxygen, on the 

 contrary it may depress and stop this activity (Alsterberg, 1922, 

 Dausend, 1931). 



Thus far we have discussed the mechanisms, pattern and bodily 

 reactions of oligochaetes, in particular Liimhricus and Tiihifex^ in 

 respiration. With the exchange of oxygen and carbon dioxide across 

 the body wall now dealt with it remains to consider the methods, if 

 any, used to transport these gases, and how they are involved in 

 cell metabolism. 



Blood Vessels and Haemoglohin 



First transport — there is an extensive closed blood system 

 composed of vessels and capillaries in the oligochaetes the exact 

 layout of which can be obtained from any standard text book such 

 as Borrodaile, Eastham, Potts and Saunders or Parker and 

 Haswell or a more detailed account is in Stephenson (1930). The 

 major vessels, one ventral and one dorsal, run longitudinally through 

 the body. In the ventral vessel blood moves to the posterior 

 extremity whilst the dorsal vessel collects blood back from the 

 segmental vessels and passes it forward. The dorsal vessel pulsates 

 as also do certain commissural vessels anteriorly, the pseudohearts. 

 The frequency with which the vessels contract varies according to 



