第8章

Mental Qualities.--There is little to be said on this head.We have seen that worms are timid.It may be doubted whether they suffer as much pain when injured, as they seem to express by their contortions.Judging by their eagerness for certain kinds of food, they must enjoy the pleasure of eating.Their sexual passion is strong enough to overcome for a time their dread of light.They perhaps have a trace of social feeling, for they are not disturbed by crawling over each other's bodies, and they sometimes lie in contact.According to Hoffmeister they pass the winter either singly or rolled up with others into a ball at the bottom of their burrows. Although worms are so remarkably deficient in the several sense-organs, this does not necessarily preclude intelligence, as we know from such cases as those of Laura Bridgman; and we have seen that when their attention is engaged, they neglect impressions to which they would otherwise have attended; and attention indicates the presence of a mind of some kind.They are also much more easily excited at certain times than at others.They perform a few actions instinctively, that is, all the individuals, including the young, perform such actions in nearly the same fashion.This is shown by the manner in which the species of Perichaeta eject their castings, so as to construct towers; also by the manner in which the burrows of the common earth-worm are smoothly lined with fine earth and often with little stones, and the mouths of their burrows with leaves.One of their strongest instincts is the plugging up the mouths of their burrows with various objects; and very young worms act in this manner.But some degree of intelligence appears, as we shall see in the next chapter, to be exhibited in this work,--a result which has surprised me more than anything else in regard to worms.

Food and Digestion.--Worms are omnivorous.They swallow an enormous quantity of earth, out of which they extract any digestible matter which it may contain; but to this subject I must recur.They also consume a large number of half-decayed leaves of all kinds, excepting a few which have an unpleasant taste or are too tough for them; likewise petioles, peduncles, and decayed flowers.But they will also consume fresh leaves, as I have found by repeated trials.According to Morren they will eat particles of sugar and liquorice; and the worms which I kept drew manybits of dry starch into their burrows, and a large bit had its angles well rounded by the fluid poured out of their mouths.But as they often drag particles of soft stone, such as of chalk, into their burrows, I feel some doubt whether the starch was used as food.Pieces of raw and roasted meat were fixed several times by long pins to the surface of the soil in my pots, and night after night the worms could be seen tugging at them, with the edges of the pieces engulfed in their mouths, so that much was consumed.Raw fat seems to be preferred even to raw meat or to any other substance which was given them, and much was consumed.They are cannibals, for the two halves of a dead worm placed in two of the pots were dragged into the burrows and gnawed; but as far as I could judge, they prefer fresh to putrid meat, and in so far I differ from Hoffmeister.

Leon Fredericq states that the digestive fluid of worms is of the same nature as the pancreatic secretion of the higher animals; and this conclusion agrees perfectly with the kinds of food which worms consume.Pancreatic juice emulsifies fat, and we have just seen how greedily worms devour fat; it dissolves fibrin, and worms eat raw meat; it converts starch into grape-sugar with wonderful rapidity, and we shall presently show that the digestive fluid of worms acts on starch. But they live chiefly on half-decayed leaves; and these would be useless to them unless they could digest the cellulose forming the cell-walls; for it is well known that all other nutritious substances are almost completely withdrawn from leaves, shortly before they fall off.It has, however, now been ascertained that some forms of cellulose, though very little or not at all attacked by the gastric secretion of the higher animals, are acted on by that from the pancreas.

The half-decayed or fresh leaves which worms intend to devour, are dragged into the mouths of their burrows to a depth of from one to three inches, and are then moistened with a secreted fluid.It has been assumed that this fluid serves to hasten their decay; but a large number of leaves were twice pulled out of the burrows of worms and kept for many weeks in a very moist atmosphere under a bell-glass in my study; and the parts which had been moistened by the worms did not decay more quickly in any plain manner than the other parts.When fresh leaves were given in theevening to worms kept in confinement and examined early on the next morning, therefore not many hours after they had been dragged into the burrows, the fluid with which they were moistened, when tested with neutral litmus paper, showed an alkaline reaction.This was repeatedly found to be the case with celery, cabbage and turnip leaves.Parts of the same leaves which had not been moistened by the worms, were pounded with a few drops of distilled water, and the juice thus extracted was not alkaline.Some leaves, however, which had been drawn into burrows out of doors, at an unknown antecedent period, were tried, and though still moist, they rarely exhibited even a trace of alkaline reaction.