CALCIFEROUS GLANDS 29 



haphazard and in most cases a momentary stoppage is followed by 

 further progress in the original direction. If it is assumed, there- 

 fore, that CO 2 may rise to a concentration of 10% in burrows it is 

 unlikely that this will cause the well-known migration which occurs 

 after heavy rain (Darwin, 1881), but it may be reflected by an 

 increased CO2 clearance from the calciferous glands (Voigt, 

 1933). 



Accumulation of carbon dioxide, whether diffusing into the 

 body from a high external concentration, or produced by metabolic 

 reactions within the body, has eff'ects upon the internal pH of the 

 animal. Particularly will this be so in the blood and coelomic fluid, 

 and it has been shown that the oxygen dissociation curve of 

 earthworm haemoglobin is aflfected by pH (Manwell, 1959). 



It is essential, therefore, that some mechanism for the regulation 

 of internal pH be active to counteract changes brought by external 

 conditions or changes in diet constitution. Experiments in which 

 earthworms were kept in 25% CO 2 for 16 hours indicate that the 

 pH of coelomic fluid remains virtually unchanged by such treat- 

 ment. This is taken to indicate that a buffering system is available 

 to maintain a constant internal pH. Removal of the calciferous 

 glands prior to treatment with 5% CO2 for 3 days, however, leads 

 to a depression of coelomic pH, i.e. an increasing acidity, 

 suggesting an accumulation of CO 2 in the system. At the end of 

 this period chemical analysis of the tissue shows that heightened 

 levels of calcium are present indicating that calcium is distributed 

 throughout the body instead of being excreted bound to CO2 

 as calcium carbonate. As a result of these experiments Dotter- 

 weich (1933) concluded that the normal activity of the calciferous 

 glands is concerned with regulating the calcium content of the 

 body and that a buffering action is possible in times of carbon 

 dioxide excess. Robertson (1936) supports this view and places 

 further stress on the probable part played by the glands in main- 

 taining acid-base balance of the body. 



Further evidence as to the working of these glands has been 

 adduced by Clark (1957). This author investigated distribution of 

 carbonic anhydrase in the tissues of the earthworm. This enzyme 

 is involved specifically in the reversible combination of CO2 

 with water to form carbonic acid (H2CO3). In vertebrates this 

 enzyme is found particularly in the red blood corpuscles, where it 



