34 



THE PHYSIOLOGY OF EARTHWORMS 



the gland its constitution has been somewhat altered. The cal- 

 careous aggregations form within the cells as a consequence and 

 are released by rupture of the cells into the lumen. 



It would seem, therefore, that the calciferous glands are an 

 organ of excretion in the earthworm, effective in salt and water 

 balance, and presumably assisting the nephridia to maintain a 

 constant internal composition by removal of calcium carbonate. 

 This would be of particular value to species living in calcareous 

 habitats. Indeed such species are known to have much larger 



Direction of blood flow 

 _^orsal "blood vesse)^ 



COz (From tissues] 



Ca (From gut) 



rbonic 

 hydrase 



Gut lumen 



Mid region 



Co CO J 

 Posterior 



Fig. 12. Formation and secretion of calcium carbonate con- 

 cretions from two areas of the calciferous glands (after van 



Gansen). 



organs than species from less calcareous soils. And its probable role 

 in the removal of carbon dioxide and maintenance of a steady 

 internal pH must not be forgotten. 



Summary 



The calciferous glands of earthworms secrete calcium carbonate 

 concretions into the lumen of the gut. Blood flows forward from 

 the intestine to these glands, the concretions are passed into the gut 

 and move posteriorly to be voided unchanged through the anus. 



