The Formation of Vegetable Mould through the Action of Worms

different occasions might be explained, either by the degree of extension of their skin and its consequent transparency, or by some particular incidence of the light; but I could discover no such relation. One thing was manifest, namely that when worms were employed in dragging leaves into their burrows or in eating them, and even during the short intervals whilst they rested from their work, they either did not perceive the light or were regardless of it; and this occurred even when the light was concentrated on them through a large lens. So, again, whilst they are paired, they will remain for an hour or two out of their burrows, fully exposed to the morning light; but it appears from what Hoffmeister says that a light will occasionally cause paired individuals to separate.

When a worm is suddenly illuminated and dashes like a rabbit into its burrow—to use the expression employed by a friend—we are at first led to look at the action as a reflex one. The irritation of the cerebral ganglia appears to cause certain muscles to contract in an inevitable manner, independently of the will or consciousness cf the animal, as if it were an automaton. But the different effect which a light produced on different occasions, and especially the fact that a worm when in any way employed and in the intervals of such employment, whatever set of muscles and ganglia may then have been brought into play, is often regardless of light, are opposed to the view of the sudden withdrawal being a simple reflex action. With the higher animals, when close attention to some abject leads to the disregard of the impressions which other objects must be producing on them, we attribute this to their attention being then absorbed; and attention implies the presence of a mind. Every sportsman knows that he can approach animals whilst they are grazing, fighting or courting, much more easily than at other times. The state, also, of the nervous system of the higher animals differs much at different times, for instance, a horse is much more readily startled at one time than at another. The comparison here implied between the actions of one of the higher animals and of one so low in the scale as an earth-worm, may appear far:

fetched; for we thus attribute to the worm attention and some mental power, neverthe- less I can see no reason to doubt the justice of the comparison. Although worms cannot be said to possess the power of vision, their sensitiveness to light enables them to distinguish between day and night; and they thus escape extreme danger from the many diurnal animals which prey on them. Their withdrawal into their burrows during the day appears, however, to have become an _ habitual action; for worms kept in pots covered by glass-plates, over which sheets of black paper were spread, and placed before a north-east win- dow, remained during the day-time in their burrows and came out every night; and they continued thus to act fora week. No doubt a little ight may have entered between the sheets of glass and the blackened paper, but we know from the trials with coloured glass, that worms are indifferent to a small amount of light.

Worms appear to be less sensitive to moderate radiant heat than to a bright light. [ judge of this from having held at different times a poker heated to dull redness near some worms, at a distance which caused a very sensible degree of warmth in my hand, One of them took no notice; a second with- drew into its burrow, but not quickly; the third and fourth much more quickly, and the fifth as quickly as possible. The light from a candle, concentrated by a lens and passing through a sheet of glass which would intercept most of the heat-rays, generally caused a much more rapid retreat than did the heated poker. Worms are sensitive to a low temper- ature, as may be inferred from their not coming out of their burrows during a frost. Worms do not possess any sense of hearing. They took not the least notice of the shrill notes from a metal whistle, which was re- peatedly sounded near them; nor did they | of the deepest and loudest tones of a bassoon, They were indifferent to shouts, if care was taken that the breath did not strike them. When placed on a table close to the keys of a piano, which was played as loudly as possible, they remained perfectly quiet. Although they are indifferent to undula- tions in the air audible by us, they are

extremely sensitive to vibrations in any solid object. When the pots containing two worms which had remained quite indifferent to the sound of the piano, were placed on this instrument, and the note C in the bass clef was struck, both instantly retreated into their burrows. After a time they emerged, and when G above the line in the treble clef was struck they again retreated. Under similar circumstances on another night one worm dashed into its burrow on a very high note being struck only once, and the other worm when C in the treble clef was struck. On these occasions the worms were not touching the sides of the pots, which stood in saucers; so that the vibrations, before reaching their bodies, had to pass from the sounding board of the piano, through the saucer, the bottom of the pot and the damp, not very compact earth on which they lay with their tails in their burrows. They often showed their sensitiveness when the pot in which they lived, or the table on which the pot stood, was accidentally and lightly struck; but they appeared less sensi- tive to such jars than to the vibrations of the

piano; and their sensitiveness to jars varied much at different times. It has often been said that if the ground is beaten or otherwise made to tremble, worms believe that they are pursued by a mole and leave their burrows. I beat the eround in many places where worms abounded, but not one emerged. When, however, the ground is dug with a fork and is violently disturbed beneath a worm, it will often crawl quickly out of its burrow. The whole body of a worm is sensitive to contact. A slight puff of air from the mouth causes an instant retreat. The glass plates placed over the pots did not fit closely, and blowing through the very narrow chinks thus left, often sufficed to cause a rapid retreat. They sometimes perceived the eddies in the air caused by quickly removing the glass plates. When a worm first comes out of its burrow, it generally moves the much ex- tended anterior extremity of its body from side to side in all directions, apparently as an organ of touch; and there is some reason to believe, as we shall see in the next chapter, that they are thus enabled to gain a general

notion of the form of an object. Of all their senses that of touch, including in this term the perception of a vibration, seems much the most highly developed. In worms the sense of smell apparently is confined to the perception of certain odours, and is feeble. They were quite indifferent to my breath, as long as I breathed on them very gently. This was tried, because it appeared possible that they might thus be warned of the approach of an enemy. They exhibited the same indifference to my breath whilst I chewed some tobacco, and while a pellet of cotton-wool with a few drops of mille-fleurs perfume or of acetic acid was kept in my mouth. Pellets of cotton-wool soaked in tobacco juice, and in millefleurs perfume, and in paraffin, were held with pincers and were waved about within two or three inches of several worms, but they took no notice. On one or two occasions, however, when acetic acid had been placed on the pellets, the worms appeared a little uneasy, and this was probably due to the irritation of their skins, The perception of such unnatural odours would be of no service to worms; and as such

timid creatures would almost certainly exhibit some signs of any new impression, we may conclude that they did not perceive these odours. The result was different when cabbage- leaves and pieces of onion were employed, both of which are devoured with much relish by worms. Small square pieces of fresh and half-decayed cabbage-leaves and of. onion bulbs were on nine occasions buried in my pots, beneath about 4 of an inch of common garden soil; and they were always discovered by the worms. One bit of cabbage was dis- covered and removed in the course of two hours; three were removed by the next morning, that is, after a single night; two others after two nights; and the seventh bit after three nights. Two pieces of onion were discovered and removed after three nights. Bits of fresh raw meat, of which worms are very fond, were buried, and were not dis- covered within forty-eight hours, during which time they had not become putrid. The earth above the various buried objects was generally pressed down only slightly, so as not to prevent the emission of any odour.

On two occasions, however, the surface was well watered, and was thus rendered some- what compact. After the bits of cabbage and onicn had been removed, I looked beneath them to see whether the worms had acci- dentally come up from below, but there was no sign of a burrow; and twice the buried | objects were laid on pieces of tin-foil which were not in the least displaced. It is of course possible that the worms whilst moving about on the surface of the ground, with their tails affixed within their burrows, may have poked their heads into the places where the above objects were buried ; but I have never seen worms acting in this manner. Some pieces of cabbage-leaf and of onion were twice buried beneath very fine ferruginous sand, which was slightly pressed down and well watered, so as to be rendered very compact, and these pieces were never discovered. On a third occasion the same kind of sand was neither pressed down nor watered, and the pieces of cabbage were discovered and_ re- moved after the second night. These several facts indicate that worms possess some power of smell; and that they. discover by this

It may be presumed that all animals which feed on various substances possess the sense of taste, and this is certainly the case with worms. Cabbage-leaves are much liked by worms; and it appears that they can dis- tinguish between different varieties; but this may perhaps be owing to differences in their texture. On eleven occasions pieces of the fresh leaves of a common green variety and of the red variety used for pickling were given them, and they preferred the green, the red being either wholly neglected or much less gnawed. On two other occasions, how- ever, they seemed to prefer the red. Half- decayed leaves of the red variety and fresh leaves of the green were attacked about equally. When leaves of the cabbage, horse- radish (a favourite food) and of the onion were given together, the latter were always and manifestly preferred. Leaves of the cabbage, lime-tree, Ampelopis, parsnip (Pastinaca), and celery (Apium) were likewise given together ; and those of the celery were first eaten. But when leaves of cabbage, turnip, beet, celery,

wild cherry and carrots were given together, the two latter kinds, especially those of the carrot, were preferred to all the others, including those of celery. It was also mani fest after many trials that wild cherry leaves were greatly preferred to those of the lime- tree and hazel (Corylus). According to Mr. Bridgman the ‘half-decayed leaves of Pilow verna are particularly liked by worms.* Pieces of the leaves of cabbage, turnip, horse-radish and onion were left on the pots during 22 days, and were all attacked and had to be renewed; but during the whole of this time leaves of an Artemisia and of the culinary sage, thyme and mint, mingled with the above leaves, were quite neglected excepting those of the mint, which were occa- sionally and very slightly nibbled. These latter four kinds of leaves do not differ in texture in a manner which could make them disagreeable to worms; they all have a strong taste, but so have the four first mentioned kinds of leaves; and the wide difference in the result must be attributed to a preference ny the worms for one taste over another,

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 remark- ably 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 thei1 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 Perichzta 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 plug- ging up the mouths of their burrows with various objects; and very young worms act in this manner. But some degree of in- telligence 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 omnivo- rous. They swallow an enormous quantity of earth, out of which they extract any diges- tible matter which it may contain; but to this subject I must recur. They also con- sume a large number of half-decayed leaves of all kinds, excepting a few which have an 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 many bits 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 eiven 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 1 could judge, they prefer fresh to putrid meat, and in so far I differ from Hoffmeister.

Léon Frédéricq 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. Pan- creatic 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 wonder- ful rapidity, and we shall presently show that the digestive fluid of worms acts on starch.7 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 otber nutri- tious substances are almost completely with- drawn from leaves, shortly before they fall off. It has, however, now been ascertained that cellulose, though very little or not at all attacked by the gastric secretion of the higher animals, is acted on by that from the pancreas.

t¢ Schmulewitsch, ‘ Action des Sucs digestifs sur la Cellulose, Bull. de PAcad. Imp. de St. Pétersbourg, tom. xxv. p. 549. 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 the evening 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. | The fluid, with which the leaves are bathed, acts on them whilst they are fresh or nearly fresh, in a remarkable manner ; for it quickly kills and discolours them. Thus the ends of a fresh carrot-leaf, which had been dragged into a burrow, were found after twelve hours of a dark brown tint. Leaves of celery, turnip, maple, elm, lime, thin leaves of ivy, and occasionally those of the cabbage were similarly acted on. The end of a leaf of Triticum repens, still attached to a growing plant, had been drawn into a burrow, and this part was dark brown and dead, whilst the rest of the leaf was fresh and green. Several leaves of lime and elm removed from burrows out of doors were found affected in different degrees. The first change appears to be that the veins become of a dull reddish-orange. The cells with chlorophyll next lose more or less completely their green colour, and their contents finally become brown. ‘The parts thus affected often appeared almost black by

reflected light; but when viewed as a trans- parent object under the microscope, minute specks of light were transmitted, and this was not the case with the unaffected parts of the*same leaves. These effects, how- ever, merely show that the secreted fluid is highly injurious or poisonous to leaves; for nearly the same effects were produced in from one to two days on various kinds of young leaves, not only by artificial pancreatic fluid, prepared with or without thymol, but quickly by a solution of thymol by itself. On one occasion leaves of Corylus were much dis- coloured by being kept for eighteen hours in pancreatic fluid, without any thymol, With young and tender leaves immersion in human saliva during rather warm weather, acted in the same manner as the pancreatic fluid, but not so quickly. The leaves in all these cases often became infiltrated with the fluid.

Large leaves from an ivy plant growing on a wall were so tough that they could not be gnawed by worms, but after four dave they were affected ina peculiar manner by the secretion poured out of their mouths. 'The upper surfaces of the leaves, over which the worms had crawled, as was shown by the dirt left on them, were marked in sinuous lines. by either a continuous or broken chain of whitish and often star-shaped dots, about 2mm. in diameter. The appearance thus pre- sented was curiously like that of a leaf, into which the larva of some minute insect had burrowed. But my son Francis, after making and examining sections, could nowhere find that the cell-walls had been broken down or that the epidermis had been penetrated. When the section passed through the whitish dots, the grains of chlorophyll were seen to be more or less discoloured, and some of the palisade and mesophyll cells contained nothing but broken down granular matter. These effects must be attributed to the trans- udation of the secretion through the epidermis into the cells.

The secretion with which worms moisten leaves likewise acts on the starch granules within the cells. My son examined some leaves of the ash and many of the lime, which had fallen off the trees and had been partly dragged into worm-burrows. It is known that with fallen leaves the starch- grains are preserved in the guard-cells of the stomata. Now in several cases the starch had partially or wholly disappeared from these cells, in the parts which had been moistened by the secretion; while they were still well pre- served in the other parts of the same leaves. Sometimes the starch was dissolved out of only one of the two guard-cells. The nucleus in one case had disappeared, together with the starch-granules. The mere burying of lime-leaves in damp earth for nine days did not cause the destruction of the starch- granules. On the other hand, the immersion of fresh lime and cherry leaves for eighteen hours in artificial pancreatic fluid, led to the dissolution of the starch-granules in the guard- cells as well as in the other cells.

From the secretion with which the leaves are moistened being alkaline, and from its acting both on the starch-granules and on the protoplasmic contents of the cells, we may infer that it resembles in nature not saliva,* but pancreatic secretion; and we know from Frédéricq that a secretion of this * Claparéde doubts whether saliva is secreted by worms: sea Zeitschrift fiir wissenschaft. Zcologie,’ B. xix. 1869, p. 601. kind is found in the intestines of worms. As the leaves which are dragged into the bur- rows are often dry and shrivelled, it is in- dispensable for their disintegration by the unarmed mouths of worms that they should first be moistened and softened; and fresh leaves, however soft and tender they may be, are similarly treated, probably from habit. The result is that they are partially digested before they are taken into the alimentary eanal. Iam not aware of any other case of extra-stomachal digestion having been re- corded. The boa-constrictor bathes its prey with saliva, but this is solely for lubricating it. Perhaps the nearest analogy may be found in such plants as Drosera and Dionza ; for here animal matter is digested and con- verted into peptone not within a stomach, but on the surfaces of the leaves.

Caleiferous Glands.—These glands (sce 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 pos- teriorly to it in Urochtea and some other genera.* The two posterior pairs are formed by lamellw, which according to Claparede, are diverticula from the cesophagus.t These lamellz are coated with a pulpy cellular layer, with the outer cells lying free in in- finite numbers. If one of these glands is punctured and sqneezed, a quantity of white pulpy matter exudes, consisting of these free cells. They are minute, and vary in diameter from 2 to 6 w 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 is added, 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 oc- casionally aggregates into small rhombic crystals or into concretions, which lie be- tween the lamelle; but I have seen only one, 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 concre- tion of carbonate of lime, as much as 1} 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 coucretions 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. Claparéde 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, lamelle 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 con-

cretion, 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 lamella must be developed in some manner. In one section made by my son, the process had apparently commenced, although the gland contained two rather large concre- tions, 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 lamelle.

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 con- cretion was removed from between two of the Jamellee within an anterior gland. It was embedded 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 Iam led to suspect that the calciferous cells are developed from the larger nucleated ones; but how this is effected was not ascertained. When an anterior gland contains several minute concretions, some of these are generally angular or crystalline in outline, while the greater number are rounded with an irregu- lar mulberry-like surface. Calciferous cells adhered to many parts of these mulberry-like masses, and their gradual disappearance could be traced while they still remained attached. It was thus evident that the concretions are formed from the lime contained within the free calciferous cells. As the smaller concre- tions increase in size, they come into eontact and unite, thus enclosing the now functionless lamella; and by such steps the formation of the largest concretions could be followed. Why the process regularly takes place in the two anterior glands, and only rarely in the four posterior glands is quite unknown. Morren says that these glands disappear

during the winter; and I have seen some instances of this fact, and others in 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 calci- ferous glands, it is probable that they pri- marily 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 sub- stances.* 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 hable 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. 7 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 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, there- fore, 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 pre- paring 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 ease 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 in- testine 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 “yeaction of the intestinal walls in the larger ‘as in the small intestine is alkaline. It “must therefore arise from acid fermentations