CHAP. I. CALCIFEROUS GLANDS. 51 



have been known to contain as much as 

 72 per cent, of lime. Worms therefore would 

 be liable to become charged with this earth, 

 unless there were some special means for its 

 excretion; and the calciferous glands are 

 well adapted for this purpose. The worms 

 which live in mould close over the chalk, 

 often have their intestines filled with this 

 substance, and their castings are almost white. 

 Here it is evident that the supply of cal- 

 careous matter must be superabundant. 

 Nevertheless with several worms collected on 

 such a site, the calciferous glands contained 

 as many free calciferous cells, and fully as 

 many and large concretions, as did the 

 glands of worms which lived where there was 

 little or no lime ; and this indicates that the 

 lime is an excretion, and not a secretion 

 poured into the alimentary canal for some 

 special purpose. 



On the other hand, the following considera- 

 tions render it highly probable that the 

 carbonate of lime, which is excreted by the 

 glands, aids the digestive process under 

 ordinary circumstances. Leaves during their 



E 2 



