Darwin 1881 was one of the first scientists to formally record that earthworms excrete calcium carbonate granules, with some up to 2 mm in diameter. However, since Darwin’s studies they have received relatively little attention. The function of the granules remains a mystery, but may be related to regulation of Ca, CO2, pH or some other as yet undiscovered metabolic process (Robertson, 1936; Piearce, 1972). There has recently been an increase in research activity focussed on earthworm calcium carbonate granules driven by the work of Canti (Canti, 1998, 2007; Canti and...

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