28 THE PHYSIOLOGY OF EARTHWORMS 



intestine, containing many metabolites and the tissue as a whole is 

 associated with many blood vessels, and in this case the calcium 

 absorbed would be eventually passed to the glands but would need 

 to be mobilized first by the chloragogen cells. 



Lastly, there is the possibility that the calciferous glands are 

 involved in acid-base balance of the body by a role in the fixation 

 of respiratory carbon dioxide. Robertson (1936) kept earthworms 

 in solutions containing either calcium nitrate or calcium chloride, 

 and after a period of one week analysed the carbon dioxide produc- 

 tion in the atmosphere, and also the amount of calcium carbonate 

 present in the soil casts of the animals. As no carbonate was present 

 in solution any carbonate appearing must have come as a result of 

 fixation of carbon dioxide from metabolic sources. The results 

 indicated that less than 10% of the atmospheric CO2 is fixed in the 

 animal body in the form of carbonate voided during casting. A 

 considerable degree of variation occurred, depending on whether 

 or not the animal was active, but an average figure of 5-3% of total 

 carbon dioxide output was produced in the form of carbonate. Con- 

 sequently Robertson believes that only a small fraction of metabolic 

 carbon dioxide is removed as carbonate. A different approach 

 has been tried by Voigt (1933). He kept earthworms in gaseous 

 atmospheres containing 14% CO2 for 5 days, or in 25% CO2 

 for 3 days. Under such conditions the contents of the calciferous 

 glands diminish and Voigt believed that in unsuitable conditions of 

 carbon dioxide stress the concretions of the calciferous glands are 

 useful in removing the gas diffusing into the body. 



An increase in the rate of secretion of the calciferous glands may 

 be caused by an increase in the atmospheric CO2, but the normal 

 concentration of CO2 is about 0-03%, and this may rise only to 

 0-25% at a soil depth of 6 inches (Russell, 1950). In wet soil, values 

 far above this may occur for short periods, and as the earthworm in 

 its burrow respires and produces carbon dioxide the concentra- 

 tion may rise even higher. 



A direct motor response to high concentrations of gaseous CO2 

 is reported by Shiraishi (1954). He passed CO2 down tubes so that 

 it impinged on Eisenia foetida crawling in the tube. If high 

 concentrations of CO2 (100-25%) are used many animals withdraw 

 their prostomium and anterior extremity and begin to take evasive 

 action. At low gas concentrations (12-5-6%) the reactions are more 



