With respect to the function of the calciferous glands, it is probable that they primarily serve as organs of excretion, and secondarily as an aid to digestion. Worms consume many fallen leaves; and it is known that lime goes on accumulating in leaves until they drop off the parent-plant, instead of being re-absorbed into the stem or roots, like various other organic and inorganic substances. {46} The ashes of a leaf of an acacia 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 calcareous matter must be super-abundant. 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 considerations 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 decay generate an abundance of various kinds of acids, which have been grouped together under the term of humus acids. We shall have to recur to this subject in our fifth chapter, and I need here only say that these acids act strongly on carbonate of lime. The half-decayed leaves which are swallowed in such large quantities by worms would, therefore, after they have been moistened and triturated in the alimentary canal, be apt to produce such acids. And in the case of several worms, the contents of the alimentary canal were found to be plainly acid, as shown by litmus paper. This acidity cannot be attributed to the nature of the digestive fluid, for pancreatic fluid is alkaline; and we have seen that the secretion which is poured out of the mouths of worms for the sake of preparing the leaves for consumption, is likewise alkaline. The acidity can hardly be due to uric acid, as the contents of the upper part of the intestine were often acid. In one case the contents of the gizzard were slightly acid, those of the upper intestines being more plainly acid. In another case the contents of the pharynx were not acid, those of the gizzard doubtfully so, while those of the intestine were distinctly acid at a distance of 5 cm. below the gizzard. Even with the higher herbivorous and omnivorous animals, the contents of the large intestine are acid. “This, however, is not caused by any acid secretion from the mucous membrane; the reaction of the intestinal walls in the larger as in