第10章

Calciferous Glands.--These glands (see Fig.1), judging from their size and from their rich supply of blood-vessels, must be of much importance to the animal.But almost as many theories have been advanced on their use as there have been observers.They consist of three pairs, which in the common earth-worm debouch into the alimentary canal in advance of the gizzard, but posteriorly to it in Urochaeta and some other genera. The two posterior pairs are formed by lamellae, which, according to Claparede, are diverticula from the oesophagus. These lamellae are coated with a pulpy cellular layer, with the outer cells lying free in infinite numbers.If one of these glands is punctured and squeezed, a quantity of white pulpy matter exudes, consisting of these free cells.They are minute, and vary in diameter from 2 to 6 microns.They contain in their centres a little excessively fine granular matter; but they look so like oil globules that Claparede and others at first treated them with ether.This produces no effect; but they are quickly dissolved with effervescence in acetic acid, and when oxalate of ammonia is added to the solution a white precipitate is thrown down.We may therefore conclude that they contain carbonate of lime.If the cells are immersed in a very little acid, they become more transparent, look like ghosts, and are soon lost to view; but if much acid isadded, they disappear instantly.After a very large number have been dissolved, a flocculent residue is left, which apparently consists of the delicate ruptured cell-walls.In the two posterior pairs of glands the carbonate of lime contained in the cells occasionally aggregates into small rhombic crystals or into concretions, which lie between the lamellae; but I have seen only one case, and Claparede only a very few such cases.

The two anterior glands differ a little in shape from the four posterior ones, by being more oval.They differ also conspicuously in generally containing several small, or two or three larger, or a single very large concretion of carbonate of lime, as much as 1.5 mm.in diameter.When a gland includes only a few very small concretions, or, as sometimes happens, none at all, it is easily overlooked.The large concretions are round or oval, and exteriorly almost smooth.One was found which filled up not only the whole gland, as is often the case, but its neck; so that it resembled an olive-oil flask in shape.These concretions when broken are seen to be more or less crystalline in structure.How they escape from the gland is a marvel; but that they do escape is certain, for they are often found in the gizzard, intestines, and in the castings of worms, both with those kept in confinement and those in a state of nature.

Claparede says very little about the structure of the two anterior glands, and he supposes that the calcareous matter of which the concretions are formed is derived from the four posterior glands.But if an anterior gland which contains only small concretions is placed in acetic acid and afterwards dissected, or if sections are made of such a gland without being treated with acid, lamellae like those in the posterior glands and coated with cellular matter could be plainly seen, together with a multitude of free calciferous cells readily soluble in acetic acid.When a gland is completely filled with a single large concretion, there are no free cells, as these have been all consumed in forming the concretion.But if such a concretion, or one of only moderately large size, is dissolved in acid, much membranous matter is left, which appears to consist of the remains of the formerly active lamellae.After the formation and expulsion of a large concretion, new lamellae must be developed in some manner.In one section made by my son, the process had apparently commenced, althoughthe gland contained two rather large concretions, for near the walls several cylindrical and oval pipes were intersected, which were lined with cellular matter and were quite filled with free calciferous cells.A great enlargement in one direction of several oval pipes would give rise to the lamellae.

Besides the free calciferous cells in which no nucleus was visible, other and rather larger free cells were seen on three occasions; and these contained a distinct nucleus and nucleolus.They were only so far acted on by acetic acid that the nucleus was thus rendered more distinct.A very small concretion was removed from between two of the lamellae within an anterior gland.It was imbedded in pulpy cellular matter, with many free calciferous cells, together with a multitude of the larger, free, nucleated cells, and these latter cells were not acted on by acetic acid, while the former were dissolved.From this and other such cases I am led to suspect that the calciferous cells are developed from the larger nucleated ones; but how this was effected was not ascertained.