CALCIFEROUS GLANDS 27 



varies only slightly. Worm casts formed after the passage of soil 

 through the gut have pH values very close to that of the parent 

 soil. Very acid substrates such as moorland peat, lemon juice and 

 other acid media have been observed to cause a decrease in the 

 secretory activity of the gland, supposed by Robinet (1883) and 

 Harrington (1899) to be due to over-production of CaCOs and 

 subsequent depletion of the gland — but suggested by Robertson, 

 with the aid of X-ray photographs, to be due to a physical dis- 

 ruption of the gland cells by the acid, and as the calcium carbonate 

 concretions can still be identified in casts from very acid media 

 they cannot play a great part in regulating intestinal pH by solution 

 in the gut contents. Rather do the other secretions of the gut, 

 enzymes and mucus, affect the intestinal pH. The optimal range of 

 enzymes for the gut is pH 6'4-7-0 (Robertson, 1936). 



The secretions of the calciferous glands also seem unlikely to 

 play much part in any other physical processes of digestion such as 

 crushing and trituration of food. The granules pass unchanged 

 along the gut, and must be of very slight importance compared 

 with the action of soil particles in crushing the food in the gut. 



The fourth hypothesis regarding the function of the calciferous 

 glands is due to M'Dowall (1926). This suggests that the calciferous 

 glands excrete excess calcium carbonate absorbed from the diet. 

 Large earthw^orms are known to favour areas in which limestone 

 and other calcareous rocks are present. In these cases an excess of 

 calcium may be taken in with the diet, but there is no direct 

 evidence that such calcium is in fact absorbed in its passage through 

 the gut. The blood supply to the glands arises from the plexal 

 vessels surrounding the rear intestine, passing anteriorly to the 

 glands. Thus if calcium is indeed absorbed in the intestine the 

 calciferous glands are well placed to remove excessive quantities 

 from the blood, by secreting the concretions into the lumen of the 

 gut. But as they do so at the anterior end of the gut the calcium 

 carbonate aggregations have again to pass along the length of the 

 intestine before reaching the exterior, perhaps indicating that 

 calcium carbonate in the diet is not absorbed, and that calcium 

 uptake is from calcium oxalate and nitrate. It is also not clear that 

 the initial absorption of materials from the gut occurs into the blood 

 vessels. Rather it would seem that the chloragogen cells are 

 the prime movers in absorption, being ideally placed along the 



