which either the anterior or posterior glands were at this season
so shrunk and empty, that they could be distinguished only with
much difficulty.

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. {25} 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