30 THE PHYSIOLOGY OF EARTHWORMS 



has a vital role in the transport of CO2 from the tissues to the 

 lungs, in the muscle tissues and pancreas. It is also particularly 

 important in parietal cells of the stomach and in the tubules of the 

 kidney, in both of which situations it is thought to be concerned 

 with the process of hydrogen ion secretion and hence is involved, 

 directly or indirectly, in acid-base reactions. 



The situation in the earthworm L. terrestris differs from that of 

 the vertebrates in that carbonic anhydrase is completely absent 

 from the blood of the animal, and thus is unable to play a part in 

 the transport of CO2, if such occurs in the blood system. The 

 enzyme is also absent from the coelomic fluid, body wall and the 



Table 4 



Carbonic Anhydrase Activity of Earthworm Tissues (From 



Clark, 1957) 



intestine. It is, however, present in the gizzard, crop, oesophagus 

 and calciferous glands, increasing in amount in that order (Table 

 4). We have noted above that carbonic anhydrase is found in 

 systems that cause shifts of pH, as during the secretion of hydro- 

 gen ions, by the same token this enzyme has been associated with 

 the solution and deposition of calcium carbonate in other situations, 

 such as during bone formation (Meldrum and Roughton, 1934), 

 and also in the laying down of the calcareous shell of some 

 molluscs (Bevelander, 1952). It thus seems likely that a similar role 

 can be postulated for carbonic anhydrase in the calciferous glands 

 of oligochaetes. 



