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Chapter 2

HABITS OF WORMS--continued.


Manner in which worms seize objects--Their power of suction--The instinct of plugging up the mouths of their burrows--Stones piled over the burrows--The advantages thus gained--Intelligence shown by worms in their manner of plugging up their burrows--Various kinds of leaves and other objects thus used--Triangles of paper--Summary of reasons for believing that worms exhibit some intelligence--Means by which they excavate their burrows, by pushing away the earth and swallowing it--Earth also swallowed for the nutritious matter which it contains--Depth to which worms burrow, and the construction of their burrows--Burrows lined with castings, and in the upper part with leaves--The lowest part paved with little stones or seeds--Manner in which the castings are ejected--The collapse of old burrows--Distribution of worms--Tower-like castings in Bengal--Gigantic castings on the Nilgiri Mountains--Castings ejected in all countries.


In the pots in which worms were kept, leaves were pinned down to the soil, and at night the manner in which they were seized could be observed. The worms always endeavoured to drag the leaves towards their burrows; and they tore or sucked off small fragments, whenever the leaves were sufficiently tender. They generally seized the thin edge of a leaf with their mouths, between the projecting upper and lower lip; the thick and strong pharynx being at the same time, as Perrier remarks, pushed forward within their bodies, so as to afford a point of resistance for the upper lip. In the case of broad flat objects they acted in a wholly different manner. The pointed anterior extremity of the body, after being brought into contact with an object of this kind, was drawn within the adjoining rings, so that it appeared truncated and became as thick as the rest of the body. This part could then be seen to swell a little; and this, I believe, is due to the pharynx being pushed a little forwards. Then by a slight withdrawal of the pharynx or by its expansion, a vacuum was produced beneath the truncated slimy end of the body whilst in contact with the object; and by this means the two adhered firmly together. {28} That under these circumstances a vacuum was produced was plainly seen on one occasion, when a large worm lying beneath a flaccid cabbage leaf tried to drag it away; for the surface of the leaf directly over the end of the worm's body became deeply pitted. On another occasion a worm suddenly lost its hold on a flat leaf; and the anterior end of the body was momentarily seen to be cup-formed. Worms can attach themselves to an object beneath water in the same manner; and I saw one thus dragging away a submerged slice of an onion-bulb.

The edges of fresh or nearly fresh leaves affixed to the ground were often nibbled by the worms; and sometimes the epidermis and all the parenchyma on one side was gnawed completely away over a considerable space; the epidermis alone on the opposite side being left quite clean. The veins were never touched, and leaves were thus sometimes partly converted into skeletons. As worms have no teeth and as their mouths consist of very soft tissue, it may be presumed that they consume by means of suction the edges and the parenchyma of fresh leaves, after they have been softened by the digestive fluid. They cannot attack such strong leaves as those of sea-kale or large and thick leaves of ivy; though one of the latter after it had become rotten was reduced in parts to the state of a skeleton.

Worms seize leaves and other objects, not only to serve as food, but for plugging up the mouths of their burrows; and this is one of their strongest instincts. They sometimes work so energetically that Mr. D. F. Simpson, who has a small walled garden where worms abound in Bayswater, informs me that on a calm damp evening he there heard so extraordinary a rustling noise from under a tree from which many leaves had fallen, that he went out with a light and discovered that the noise was caused by many worms dragging the dry leaves and squeezing them into the burrows. Not only leaves, but petioles of many kinds, some flower-peduncles, often decayed twigs of trees, bits of paper, feathers, tufts of wool and horse- hairs are dragged into their burrows for this purpose. I have seen as many as seventeen petioles of a Clematis projecting from the mouth of one burrow, and ten from the mouth of another. Some of these objects, such as the petioles just named, feathers, &c., are never gnawed by worms. In a gravel-walk in my garden I found many hundred leaves of a pine-tree (P. austriaca or nigricans) drawn by their bases into burrows. The surfaces by which these leaves are articulated to the branches are shaped in as peculiar a manner as is the joint between the leg-bones of a quadruped; and if these surfaces had been in the least gnawed, the fact would have been immediately visible, but there was no trace of gnawing. Of ordinary dicotyledonous leaves, all those which are dragged into burrows are not gnawed. I have seen as many as nine leaves of the lime-tree drawn into the same burrow, and not nearly all of them had been gnawed; but such leaves may serve as a store for future consumption. Where fallen leaves are abundant, many more are sometimes collected over the mouth of a burrow than can be used, so that a small pile of unused leaves is left like a roof over those which have been partly dragged in.

A leaf in being dragged a little way into a cylindrical burrow is necessarily much folded or crumpled. When another leaf is drawn in, this is done exteriorly to the first one, and so on with the succeeding leaves; and finally all become closely folded and pressed together. Sometimes the worm enlarges the mouth of its burrow, or makes a fresh one close by, so as to draw in a still larger number of leaves. They often or generally fill up the interstices between the drawn-in leaves with moist viscid earth ejected from their bodies; and thus the mouths of the burrows are securely plugged. Hundreds of such plugged burrows may be seen in many places, especially during the autumnal and early winter months. But, as will hereafter be shown, leaves are dragged into the burrows not only for plugging them up and for food, but for the sake of lining the upper part or mouth.

When worms cannot obtain leaves, petioles, sticks, &c., with which to plug up the mouths of their burrows, they often protect them by little heaps of stones; and such heaps of smooth rounded pebbles may frequently be seen on gravel-walks. Here there can be no question about food. A lady, who was interested in the habits of worms, removed the little heaps of stones from the mouths of several burrows and cleared the surface of the ground for some inches all round. She went out on the following night with a lantern, and saw the worms with their tails fixed in their burrows, dragging the stones inwards by the aid of their mouths, no doubt by suction. "After two nights some of the holes had 8 or 9 small stones over them; after four nights one had about 30, and another 34 stones." {29} One stone--which had been dragged over the gravel-walk to the mouth of a burrow weighed two ounces; and this proves how strong worms are. But they show greater strength in sometimes displacing stones in a well-trodden gravel-walk; that they do so, may be inferred from the cavities left by the displaced stones being exactly filled by those lying over the mouths of adjoining burrows, as I have myself observed.

Work of this kind is usually performed during the night; but I have occasionally known objects to be drawn into the burrows during the day. What advantage the worms derive from plugging up the mouths of their burrows with leaves, &c., or from piling stones over them, is doubtful. They do not act in this manner at the times when they eject much earth from their burrows; for their castings then serve to cover the mouths. When gardeners wish to kill worms on a lawn, it is necessary first to brush or rake away the castings from the surface, in order that the lime-water may enter the burrows. {30} It might be inferred from this fact that the mouths are plugged up with leaves, &c., to prevent the entrance of water during heavy rain; but it may be urged against this view that a few, loose, well-rounded stones are ill-adapted to keep out water. I have moreover seen many burrows in the perpendicularly cut turf-edgings to gravel-walks, into which water could hardly flow, as well plugged as burrows on a level surface. It is not probable that the plugs or piles of stones serve to conceal the burrows from scolopendras, which, according to Hoffmeister, {31} are the bitterest enemies of worms, or from the larger species of Carabus and Staphylinus which attack them ferociously, for these animals are nocturnal, and the burrows are opened at night. May not worms when the mouth of the burrow is protected be able to remain with safety with their heads close to it, which we know that they like to do, but which costs so many of them their lives? Or may not the plugs check the free ingress of the lowest stratum of air, when chilled by radiation at night, from the surrounding ground and herbage? I am inclined to believe in this latter view: firstly, because when worms were kept in pots in a room with a fire, in which case cold air could not enter the burrows, they plugged them up in a slovenly manner; and secondarily, because they often coat the upper part of their burrows with leaves, apparently to prevent their bodies from coming into close contact with the cold damp earth. Mr. E. Parfitt has suggested to me that the mouths of the burrows are closed in order that the air within them may be kept thoroughly damp, and this seems the most probable explanation of the habit. But the plugging-up process may serve for all the above purposes.

Whatever the motive may be, it appears that worms much dislike leaving the mouths of their burrows open. Nevertheless they will reopen them at night, whether or not they can afterwards close them. Numerous open burrows may be seen on recently-dug ground, for in this case the worms eject their castings in cavities left in the ground, or in the old burrows instead of piling them over the mouths of their burrows, and they cannot collect objects on the surface by which the mouths might be protected. So again on a recently disinterred pavement of a Roman villa at Abinger (hereafter to be described) the worms pertinaciously opened their burrows almost every night, when these had been closed by being trampled on, although they were rarely able to find a few minute stones wherewith to protect them.

Intelligence shown by worms in their manner of plugging up their burrows.--If a man had to plug up a small cylindrical hole, with such objects as leaves, petioles or twigs, he would drag or push them in by their pointed ends; but if these objects were very thin relatively to the size of the hole, he would probably insert some by their thicker or broader ends. The guide in his case would be intelligence. It seemed therefore worth while to observe carefully how worms dragged leaves into their burrows; whether by their tips or bases or middle parts. It seemed more especially desirable to do this in the case of plants not natives to our country; for although the habit of dragging leaves into their burrows is undoubtedly instinctive with worms, yet instinct could not tell them how to act in the case of leaves about which their progenitors knew nothing. If, moreover, worms acted solely through instinct or an unvarying inherited impulse, they would draw all kinds of leaves into their burrows in the same manner. If they have no such definite instinct, we might expect that chance would determine whether the tip, base or middle was seized. If both these alternatives are excluded, intelligence alone is left; unless the worm in each case first tries many different methods, and follows that alone which proves possible or the most easy; but to act in this manner and to try different methods makes a near approach to intelligence.

In the first place 227 withered leaves of various kinds, mostly of English plants, were pulled out of worm-burrows in several places. Of these, 181 had been drawn into the burrows by or near their tips, so that the foot-stalk projected nearly upright from the mouth of the burrow; 20 had been drawn in by their bases, and in this case the tips projected from the burrows; and 26 had been seized near the middle, so that these had been drawn in transversely and were much crumpled. Therefore 80 per cent. (always using the nearest whole number) had been drawn in by the tip, 9 per cent. by the base or foot-stalk, and 11 per cent. transversely or by the middle. This alone is almost sufficient to show that chance does not determine the manner in which leaves are dragged into the burrows.

Of the above 227 leaves, 70 consisted of the fallen leaves of the common lime-tree, which is almost certainly not a native of England. These leaves are much acuminated towards the tip, and are very broad at the base with a well-developed foot-stalk. They are thin and quite flexible when half-withered. Of the 70, 79 per cent. had been drawn in by or near the tip; 4 per cent. by or near the base; and 17 per cent. transversely or by the middle. These proportions agree very closely, as far as the tip is concerned, with those before given. But the percentage drawn in by the base is smaller, which may be attributed to the breadth of the basal part of the blade. We here, also, see that the presence of a foot- stalk, which it might have been expected would have tempted the worms as a convenient handle, has little or no influence in determining the manner in which lime leaves are dragged into the burrows. The considerable proportion, viz., 17 per cent., drawn in more or less transversely depends no doubt on the flexibility of these half-decayed leaves. The fact of so many having been drawn in by the middle, and of some few having been drawn in by the base, renders it improbable that the worms first tried to draw in most of the leaves by one or both of these methods, and that they afterwards drew in 79 per cent. by their tips; for it is clear that they would not have failed in drawing them in by the base or middle.

The leaves of a foreign plant were next searched for, the blades of which were not more pointed towards the apex than towards the base. This proved to be the case with those of a laburnum (a hybrid between Cytisus alpinus and laburnum) for on doubling the terminal over the basal half, they generally fitted exactly; and when there was any difference, the basal half was a little the narrower. It might, therefore, have been expected that an almost equal number of these leaves would have been drawn in by the tip and base, or a slight excess in favour of the latter. But of 73 leaves (not included in the first lot of 227) pulled out of worm-burrows, 63 per cent. had been drawn in by the tip; 27 per cent. by the base, and 10 per cent. transversely. We here see that a far larger proportion, viz., 27 per cent. were drawn in by the base than in the case of lime leaves, the blades of which are very broad at the base, and of which only 4 per cent. had thus been drawn in. We may perhaps account for the fact of a still larger proportion of the laburnum leaves not having been drawn in by the base, by worms having acquired the habit of generally drawing in leaves by their tips and thus avoiding the foot-stalk. For the basal margin of the blade in many kinds of leaves forms a large angle with the foot- stalk; and if such a leaf were drawn in by the foot-stalk, the basal margin would come abruptly into contact with the ground on each side of the burrow, and would render the drawing in of the leaf very difficult.

Nevertheless worms break through their habit of avoiding the foot- stalk, if this part offers them the most convenient means for drawing leaves into their burrows. The leaves of the endless hybridised varieties of the Rhododendron vary much in shape; some are narrowest towards the base and others towards the apex. After they have fallen off, the blade on each side of the midrib often becomes curled up while drying, sometimes along the whole length, sometimes chiefly at the base, sometimes towards the apex. Out of 28 fallen leaves on one bed of peat in my garden, no less than 23 were narrower in the basal quarter than in the terminal quarter of their length; and this narrowness was chiefly due to the curling in of the margins. Out of 36 fallen leaves on another bed, in which different varieties of the Rhododendron grew, only 17 were narrower towards the base than towards the apex. My son William, who first called my attention to this case, picked up 237 fallen leaves in his garden (where the Rhododendron grows in the natural soil) and of these 65 per cent. could have been drawn by worms into their burrows more easily by the base or foot-stalk than by the tip; and this was partly due to the shape of the leaf and in a less degree to the curling in of the margins: 27 per cent. could have been drawn in more easily by the tip than by the base: and 8 per cent. with about equal ease by either end. The shape of a fallen leaf ought to be judged of before one end has been drawn into a burrow, for after this has happened, the free end, whether it be the base or apex, will dry more quickly than the end imbedded in the damp ground; and the exposed margins of the free end will consequently tend to become more curled inwards than they were when the leaf was first seized by the worm. My son found 91 leaves which had been dragged by worms into their burrows, though not to a great depth; of these 66 per cent. had been drawn in by the base or foot-stalk; and 34 per cent, by the tip. In this case, therefore, the worms judged with a considerable degree of correctness how best to draw the withered leaves of this foreign plant into their burrows; notwithstanding that they had to depart from their usual habit of avoiding the foot-stalk.

On the gravel-walks in my garden a very large number of leaves of three species of Pinus (P. austriaca, nigricans and sylvestris) are regularly drawn into the mouths of worm burrows. These leaves consist of two so-called needles, which are of considerable length in the two first and short in the last named species, and are united to a common base; and it is by this part that they are almost invariably drawn into the burrows. I have seen only two or at most three exceptions to this rule with worms in a state of nature. As the sharply pointed needles diverge a little, and as several leaves are drawn into the same burrow, each tuft forms a perfect chevaux de frise. On two occasions many of these tufts were pulled up in the evening, but by the following morning fresh leaves had been pulled in, and the burrows were again well protected. These leaves could not be dragged into the burrows to any depth, except by their bases, as a worm cannot seize hold of the two needles at the same time, and if one alone were seized by the apex, the other would be pressed against the ground and would resist the entry of the seized one. This was manifest in the above mentioned two or three exceptional cases. In order, therefore, that worms should do their work well, they must drag pine-leaves into their burrows by their bases, where the two needles are conjoined. But how they are guided in this work is a perplexing question.

This difficulty led my son Francis and myself to observe worms in confinement during several nights by the aid of a dim light, while they dragged the leaves of the above named pines into their burrows. They moved the anterior extremities of their bodies about the leaves, and on several occasions when they touched the sharp end of a needle they withdrew suddenly as if pricked. But I doubt whether they were hurt, for they are indifferent to very sharp objects, and will swallow even rose-thorns and small splinters of glass. It may also be doubted, whether the sharp ends of the needles serve to tell them that this is the wrong end to seize; for the points were cut off many leaves for a length of about one inch, and fifty-seven of them thus treated were drawn into the burrows by their bases, and not one by the cut-off ends. The worms in confinement often seized the needles near the middle and drew them towards the mouths of their burrows; and one worm tried in a senseless manner to drag them into the burrow by bending them. They sometimes collected many more leaves over the mouths of their burrows (as in the case formerly mentioned of lime-leaves) than could enter them. On other occasions, however, they behaved very differently; for as soon as they touched the base of a pine-leaf, this was seized, being sometimes completely engulfed in their mouths, or a point very near the base was seized, and the leaf was then quickly dragged or rather jerked into their burrows. It appeared both to my son and myself as if the worms instantly perceived as soon as they had seized a leaf in the proper manner. Nine such cases were observed, but in one of them the worm failed to drag the leaf into its burrow, as it was entangled by other leaves lying near. In another case a leaf stood nearly upright with the points of the needles partly inserted into a burrow, but how placed there was not seen; and then the worm reared itself up and seized the base, which was dragged into the mouth of the burrow by bowing the whole leaf. On the other hand, after a worm had seized the base of a leaf, this was on two occasions relinquished from some unknown motive.

As already remarked, the habit of plugging up the mouths of the burrows with various objects, is no doubt instinctive in worms; and a very young one, born in one of my pots, dragged for some little distance a Scotch-fir leaf, one needle of which was as long and almost as thick as its own body. No species of pine is endemic in this part of England, it is therefore incredible that the proper manner of dragging pine-leaves into the burrows can be instinctive with our worms. But as the worms on which the above observations were made, were dug up beneath or near some pines, which had been planted there about forty years, it was desirable to prove that their actions were not instinctive. Accordingly, pine-leaves were scattered on the ground in places far removed from any pine-tree, and 90 of them were drawn into the burrows by their bases. Only two were drawn in by the tips of the needles, and these were not real exceptions, as one was drawn in for a very short distance, and the two needles of the other cohered. Other pine-leaves were given to worms kept in pots in a warm room, and here the result was different; for out of 42 leaves drawn into the burrows, no less than i6 were drawn in by the tips of the needles. These worms, however, worked in a careless or slovenly manner; for the leaves were often drawn in to only a small depth; sometimes they were merely heaped over the mouths of the burrows, and sometimes none were drawn in. I believe that this carelessness may be accounted for either by the warmth of the air, or by its dampness, as the pots were covered by glass plates; the worms consequently did not care about plugging up their holes effectually. Pots tenanted by worms and covered with a net which allowed the free entrance of air, were left out of doors for several nights, and now 72 leaves were all properly drawn in by their bases.

It might perhaps be inferred from the facts as yet given, that worms somehow gain a general notion of the shape or structure of pine-leaves, and perceive that it is necessary for them to seize the base where the two needles are conjoined. But the following cases make this more than doubtful. The tips of a large number of needles of P. austriaca were cemented together with shell-lac dissolved in alcohol, and were kept for some days, until, as I believe, all odour or taste had been lost; and they were then scattered on the ground where no pine-trees grew, near burrows from which the plugging had been removed. Such leaves could have been drawn into the burrows with equal ease by either end; and judging from analogy and more especially from the case presently to be given of the petioles of Clematis montana, I expected that the apex would have been preferred. But the result was that out of 121 leaves with the tips cemented, which were drawn into burrows, 108 were drawn in by their bases, and only 13 by their tips. Thinking that the worms might possibly perceive and dislike the smell or taste of the shell-lac, though this was very improbable, especially after the leaves had been left out during several nights, the tips of the needles of many leaves were tied together with fine thread. Of leaves thus treated 150 were drawn into burrows--123 by the base and 27 by the tied tips; so that between four land five times as many were drawn in by the base as by the tip. It is possible that the short cut-off ends of the thread with which they were tied, may have tempted the worms to drag in a larger proportional number by the tips than when cement was used. Of the leaves with tied and cemented tips taken together (271 in number) 85 per cent. were drawn in by the base and 15 per cent. by the tips. We may therefore infer that it is not the divergence of the two needles which leads worms in a state of nature almost invariably to drag pine-leaves into their burrows by the base. Nor can it be the sharpness of the points of the needles which determines them; for, as we have seen, many leaves with the points cut off were drawn in by their bases. We are thus led to conclude, that with pine-leaves there must be something attractive to worms in the base, notwithstanding that few ordinary leaves are drawn in by the base or foot-stalk.

Petioles.--We will now turn to the petioles or foot-stalks of compound leaves, after the leaflets have fallen off. Those from Clematis montana, which grew over a verandah, were dragged early in January in large numbers into the burrows on an adjoining gravel- walk, lawn, and flower-bed. These petioles vary from 2.5 to 4.5 inches in length, are rigid and of nearly uniform thickness, except close to the base where they thicken rather abruptly, being here about twice as thick as in any other part. The apex is somewhat pointed, but soon withers and is then easily broken off. Of these petioles, 314 were pulled out of burrows in the above specified sites; and it was found that 76 per cent. had been drawn in by their tips, and 24 per cent by their bases; so that those drawn in by the tip were a little more than thrice as many as those drawn in by the base. Some of those extracted from the well-beaten gravel- walk were kept separate from the others; and of these (59 in number) nearly five times as many had been drawn in by the tip as by the base; whereas of those extracted from the lawn and flower- bed, where from the soil yielding more easily, less care would be necessary in plugging up the burrows, the proportion of those drawn in by the tip (130) to those drawn in by the base (48) was rather less than three to one. That these petioles had been dragged into the burrows for plugging them up, and not for food, was manifest, as neither end, as far as I could see, had been gnawed. As several petioles are used to plug up the same burrow, in one case as many as 10, and in another case as many as 15, the worms may perhaps at first draw in a few by the thicker end so as to save labour; but afterwards a large majority are drawn in by the pointed end, in order to plug up the hole securely.

The fallen petioles of our native ash-tree were next observed, and the rule with most objects, viz., that a large majority are dragged into the burrows by the more pointed end, had not here been followed; and this fact much surprised me at first. These petioles vary in length from 5 to 8.5 inches; they are thick and fleshy towards the base, whence they taper gently towards the apex, which is a little enlarged and truncated where the terminal leaflet had been originally attached. Under some ash-trees growing in a grass- field, 229 petioles were pulled out of worm burrows early in January, and of these 51.5 per cent. had been drawn in by the base, and 48.5 per cent. by the apex. This anomaly was however readily explained as soon as the thick basal part was examined; for in 78 out of 103 petioles, this part had been gnawed by worms, just above the horse-shoe shaped articulation. In most cases there could be no mistake about the gnawing; for ungnawed petioles which were examined after being exposed to the weather for eight additional weeks had not become more disintegrated or decayed near the base than elsewhere. It is thus evident that the thick basal end of the petiole is drawn in not solely for the sake of plugging up the mouths of the burrows, but as food. Even the narrow truncated tips of some few petioles had been gnawed; and this was the case in 6 out of 37 which were examined for this purpose. Worms, after having drawn in and gnawed the basal end, often push the petioles out of their burrows; and then drag in fresh ones, either by the base for food, or by the apex for plugging up the mouth more effectually. Thus, out of 37 petioles inserted by their tips, 5 had been previously drawn in by the base, for this part had been gnawed. Again, I collected a handful of petioles lying loose on the ground close to some plugged-up burrows, where the surface was thickly strewed with other petioles which apparently had never been touched by worms; and 14 out of 47 (i.e. nearly one-third), after having had their bases gnawed had been pushed out of the burrows and were now lying on the ground. From these several facts we may conclude that worms draw in some petioles of the ash by the base to serve as food, and others by the tip to plug up the mouths of their burrows in the most efficient manner.

The petioles of Robinia pseudo-acacia vary from 4 or 5 to nearly 12 inches in length; they are thick close to the base before the softer parts have rotted off, and taper much towards the upper end. They are so flexible that I have seen some few doubled up and thus drawn into the burrows of worms. Unfortunately these petioles were not examined until February, by which time the softer parts had completely rotted off, so that it was impossible to ascertain whether worms had gnawed the bases, though this is in itself probable. Out of 121 petioles extracted from burrows early in February, 68 were imbedded by the base, and 53 by the apex. On February 5 all the petioles which had been drawn into the burrows beneath a Robinia, were pulled up; and after an interval of eleven days, 35 petioles had been again dragged in, 19 by the base, and 16 by the apex. Taking these two lots together, 56 per cent. were drawn in by the base, and 44 per cent. by the apex. As all the softer parts had long ago rotted off, we may feel sure, especially in the latter case, that none had been drawn in as food. At this season, therefore, worms drag these petioles into their burrows indifferently by either end, a slight preference being given to the base. This latter fact may be accounted for by the difficulty of plugging up a burrow with objects so extremely thin as are the upper ends. In support of this view, it may be stated that out of the 16 petioles which had been drawn in by their upper ends, the more attenuated terminal portion of 7 had been previously broken off by some accident.

Triangles of paper.--Elongated triangles were cut out of moderately stiff writing-paper, which was rubbed with raw fat on both sides, so as to prevent their becoming excessively limp when exposed at night to rain and dew. The sides of all the triangles were three inches in length, with the bases of 120 one inch, and of the other 183 half an inch in length. These latter triangles were very narrow or much acuminated. {32} As a check on the observations presently to be given, similar triangles in a damp state were seized by a very narrow pair of pincers at different points and at all inclinations with reference to the margins, and were then drawn into a short tube of the diameter of a worm-burrow. If seized by the apex, the triangle was drawn straight into the tube, with its margins infolded; if seized at some little distance from the apex, for instance at half an inch, this much was doubled back within the tube. So it was with the base and basal angles, though in this case the triangles offered, as might have been expected, much more resistance to being drawn in. If seized near the middle the triangle was doubled up, with the apex and base left sticking out of the tube. As the sides of the triangles were three inches in length, the result of their being drawn into a tube or into a burrow in different ways, may be conveniently divided into three groups: those drawn in by the apex or within an inch of it; those drawn in by the base or within an inch of it; and those drawn in by any point in the middle inch.

In order to see how the triangles would be seized by worms, some in a damp state were given to worms kept in confinement. They were seized in three different manners in the case of both the narrow and broad triangles: viz., by the margin; by one of the three angles, which was often completely engulfed in their mouths; and lastly, by suction applied to any part of the flat surface. If lines parallel to the base and an inch apart, are drawn across a triangle with the sides three inches in length, it will be divided into three parts of equal length. Now if worms seized indifferently by chance any part, they would assuredly seize on the basal part or division far oftener than on either of the two other divisions. For the area of the basal to the apical part is as 5 to 1, so that the chance of the former being drawn into a burrow by suction, will be as 5 to 1, compared with the apical part. The base offers two angles and the apex only one, so that the former would have twice as good a chance (independently of the size of the angles) of being engulfed in a worm's mouth, as would the apex. It should, however, be stated that the apical angle is not often seized by worms; the margin at a little distance on either side being preferred. I judge of this from having found in 40 out of 46 cases in which triangles had been drawn into burrows by their apical ends, that the tip had been doubled back within the burrow for a length of between 1/20 of an inch and 1 inch. Lastly, the proportion between the margins of the basal and apical parts is as 3 to 2 for the broad, and 2.5 to 2 for the narrow triangles. From these several considerations it might certainly have been expected, supposing that worms seized hold of the triangles by chance, that a considerably larger proportion would have been dragged into the burrows by the basal than by the apical part; but we shall immediately see how different was the result.

Triangles of the above specified sizes were scattered on the ground in many places and on many successive nights near worm-burrows, from which the leaves, petioles, twigs, &c., with which they had been plugged, were removed. Altogether 303 triangles were drawn by worms into their burrows: 12 others were drawn in by both ends, but as it was impossible to judge by which end they had been first seized, these are excluded. Of the 303, 62 per cent. had been drawn in by the apex (using this term for all drawn in by the apical part, one inch in length); 15 per cent. by the middle; and 23 per cent. by the basal part. If they had been drawn indifferently by any point, the proportion for the apical, middle and basal parts would have been 33.3 per cent. for each; but, as we have just seen, it might have been expected that a much larger proportion would have been drawn in by the basal than by any other part. As the case stands, nearly three times as many were drawn in by the apex as by the base. If we consider the broad triangles by themselves, 59 per cent. were drawn in by the apex, 25 per cent. by the middle, and 16 per cent. by the base. Of the narrow triangles, 65 per cent. were drawn in by the apex, 14 per cent, by the middle, and 21 per cent. by the base; so that here those drawn in by the apex were more than 3 times as many as those drawn in by the base. We may therefore conclude that the manner in which the triangles are drawn into the burrows is not a matter of chance.

In eight cases, two triangles had been drawn into the same burrow, and in seven of these cases, one had been drawn in by the apex and the other by the base. This again indicates that the result is not determined by chance. Worms appear sometimes to revolve in the act of drawing in the triangles, for five out of the whole lot had been wound into an irregular spire round the inside of the burrow. Worms kept in a warm room drew 63 triangles into their burrows; but, as in the case of the pine-leaves, they worked in a rather careless manner, for only 44 per cent. were drawn in by the apex, 22 per cent. by the middle, and 33 per cent. by the base. In five cases, two triangles were drawn into the same burrow.

It may be suggested with much apparent probability that so large a proportion of the triangles were drawn in by the apex, not from the worms having selected this end as the most convenient for the purpose, but from having first tried in other ways and failed. This notion was countenanced by the manner in which worms in confinement were seen to drag about and drop the triangles; but then they were working carelessly. I did not at first perceive the importance of this subject, but merely noticed that the bases of those triangles which had been drawn in by the apex, were generally clean and not crumpled. The subject was afterwards attended to carefully. In the first place several triangles which had been drawn in by the basal angles, or by the base, or a little above the base, and which were thus much crumpled and dirtied, were left for some hours in water and were then well shaken while immersed; but neither the dirt nor the creases were thus removed. Only slight creases could be obliterated, even by pulling the wet triangles several times through my fingers. Owing to the slime from the worms' bodies, the dirt was not easily washed off. We may therefore conclude that if a triangle, before being dragged in by the apex, had been dragged into a burrow by its base with even a slight degree of force, the basal part would long retain its creases and remain dirty. The condition of 89 triangles (65 narrow and 24 broad ones), which had been drawn in by the apex, was observed; and the bases of only 7 of them were at all creased, being at the same time generally dirty. Of the 82 uncreased triangles, 14 were dirty at the base; but it does not follow from this fact that these had first been dragged towards the burrows by their bases; for the worms sometimes covered large portions of the triangles with slime, and these when dragged by the apex over the ground would be dirtied; and during rainy weather, the triangles were often dirtied over one whole side or over both sides. If the worms had dragged the triangles to the mouths of their burrows by their bases, as often as by their apices, and had then perceived, without actually trying to draw them into the burrow, that the broader end was not well adapted for this purpose--even in this case a large proportion would probably have had their basal ends dirtied. We may therefore infer--improbable as is the inference-- that worms are able by some means to judge which is the best end by which to draw triangles of paper into their burrows.

The percentage results of the foregoing observations on the manner in which worms draw various kinds of objects into the mouths of their burrows may be abridged as follows:-

Drawn into the Drawn in, Drawn in, Nature of Object. burrows, by or by or by or near near near the the the apex. middle. base. Leaves of various kinds 80 11 9 - of the Lime, basal margin of blade broad, apex acuminated 79 17 4 - of a Laburnum, basal part of blade as narrow as, or some- times little narrower than the apical part 63 10 27 - of the Rhododendron, basal part of blade often narrower than the apical part 34 ... 66 - of Pine-trees, consisting of two needles arising from a common base ... ... 100 Petioles of a Clematis, somewhat pointed at the apex, and blunt at the base 76 ... 24 - of the Ash, the thick basal end often drawn in to serve as food 48.5 ... 51.5 - of Robinia, extremely thin, especially towards the apex, so as to be ill-fitted for plugging up the burrows 44 ... 56 Triangles of paper, of the two sizes 62 15 23 - of the broad ones alone 59 25 16 - of the narrow ones alone 65 14 21

If we consider these several cases, we can hardly escape from the conclusion that worms show some degree of intelligence in their manner of plugging up their burrows. Each particular object is seized in too uniform a manner, and from causes which we can generally understand, for the result to be attributed to mere chance. That every object has not been drawn in by its pointed end, may be accounted for by labour having been saved through some being inserted by their broader or thicker ends. No doubt worms are led by instinct to plug up their burrows; and it might have been expected that they would have been led by instinct how best to act in each particular case, independently of intelligence. We see how difficult it is to judge whether intelligence comes into play, for even plants might sometimes be thought to be thus directed; for instance when displaced leaves re-direct their upper surfaces towards the light by extremely complicated movements and by the shortest course. With animals, actions appearing due to intelligence may be performed through inherited habit without any intelligence, although aboriginally thus acquired. Or the habit may have been acquired through the preservation and inheritance of beneficial variations of some other habit; and in this case the new habit will have been acquired independently of intelligence throughout the whole course of its development. There is no a priori improbability in worms having acquired special instincts through either of these two latter means. Nevertheless it is incredible that instincts should have been developed in reference to objects, such as the leaves of petioles of foreign plants, wholly unknown to the progenitors of the worms which act in the described manner. Nor are their actions so unvarying or inevitable as are most true instincts.

As worms are not guided by special instincts in each particular case, though possessing a general instinct to plug up their burrows, and as chance is excluded, the next most probable conclusion seems to be that they try in many different ways to draw in objects, and at last succeed in some one way. But it is surprising that an animal so low in the scale as a worm should have the capacity for acting in this manner, as many higher animals have no such capacity. For instance, ants may be seen vainly trying to drag an object transversely to their course, which could be easily drawn longitudinally; though after a time they generally act in a wiser manner, M. Fabre states {33} that a Sphex--an insect belonging to the same highly-endowed order with ants--stocks its nest with paralysed grass-hoppers, which are invariably dragged into the burrow by their antennae. When these were cut off close to the head, the Sphex seized the palpi; but when these were likewise cut off, the attempt to drag its prey into the burrow was given up in despair. The Sphex had not intelligence enough to seize one of the six legs or the ovipositor of the grasshopper, which, as M. Fabre remarks, would have served equally well. So again, if the paralysed prey with an egg attached to it be taken out of the cell, the Sphex after entering and finding the cell empty, nevertheless closes it up in the usual elaborate manner. Bees will try to escape and go on buzzing for hours on a window, one half of which has been left open. Even a pike continued during three months to dash and bruise itself against the glass sides of an aquarium, in the vain attempt to seize minnows on the opposite side. {34} A cobra-snake was seen by Mr. Layard {35} to act much more wisely than either the pike or the Sphex; it had swallowed a toad lying within a hole, and could not withdraw its head; the toad was disgorged, and began to crawl away; it was again swallowed and again disgorged; and now the snake had learnt by experience, for it seized the toad by one of its legs and drew it out of the hole. The instincts of even the higher animals are often followed in a senseless or purposeless manner: the weaver-bird will perseveringly wind threads through the bars of its cage, as if building a nest: a squirrel will pat nuts on a wooden floor, as if he had just buried them in the ground: a beaver will cut up logs of wood and drag them about, though there is no water to dam up; and so in many other cases.

Mr. Romanes, who has specially studied the minds of animals, believes that we can safely infer intelligence, only when we see an individual profiting by its own experience. By this test the cobra showed some intelligence; but this would have been much plainer if on a second occasion he had drawn a toad out of a hole by its leg. The Sphex failed signally in this respect. Now if worms try to drag objects into their burrows first in one way and then in another, until they at last succeed, they profit, at least in each particular instance, by experience.

But evidence has been advanced showing that worms do not habitually try to draw objects into their burrows in many different ways. Thus half-decayed lime-leaves from their flexibility could have been drawn in by their middle or basal parts, and were thus drawn into the burrows in considerable numbers; yet a large majority were drawn in by or near the apex. The petioles of the Clematis could certainly have been drawn in with equal ease by the base and apex; yet three times and in certain cases five times as many were drawn in by the apex as by the base. It might have been thought that the foot-stalks of leaves would have tempted the worms as a convenient handle; yet they are not largely used, except when the base of the blade is narrower than the apex. A large number of the petioles of the ash are drawn in by the base; but this part serves the worms as food. In the case of pine-leaves worms plainly show that they at least do not seize the leaf by chance; but their choice does not appear to be determined by the divergence of the two needles, and the consequent advantage or necessity of drawing them into their burrows by the base. With respect to the triangles of paper, those which had been drawn in by the apex rarely had their bases creased or dirty; and this shows that the worms had not often first tried to drag them in by this end.

If worms are able to judge, either before drawing or after having drawn an object close to the mouths of their burrows, how best to drag it in, they must acquire some notion of its general shape. This they probably acquire by touching it in many places with the anterior extremity of their bodies, which serves as a tactile organ. It may be well to remember how perfect the sense of touch becomes in a man when born blind and deaf, as are worms. If worms have the power of acquiring some notion, however rude, of the shape of an object and of their burrows, as seems to be the case, they deserve to be called intelligent; for they then act in nearly the same manner as would a man under similar circumstances.

To sum up, as chance does not determine the manner in which objects are drawn into the burrows, and as the existence of specialized instincts for each particular case cannot be admitted, the first and most natural supposition is that worms try all methods until they at last succeed; but many appearances are opposed to such a supposition. One alternative alone is left, namely, that worms, although standing low in the scale of organization, possess some degree of intelligence. This will strike every one as very improbable; but it may be doubted whether we know enough about the nervous system of the lower animals to justify our natural distrust of such a conclusion. With respect to the small size of the cerebral ganglia, we should remember what a mass of inherited knowledge, with some power of adapting means to an end, is crowded into the minute brain of a worker-ant.

Means by which worms excavate their burrows.--This is effected in two ways; by pushing away the earth on all sides, and by swallowing it. In the former case, the worm inserts the stretched out and attenuated anterior extremity of its body into any little crevice, or hole; and then, as Perrier remarks, {36} the pharynx is pushed forwards into this part, which consequently swells and pushes away the earth on all sides. The anterior extremity thus serves as a wedge. It also serves, as we have before seen, for prehension and suction, and as a tactile organ. A worm was placed on loose mould, and it buried itself in between two and three minutes. On another occasion four worms disappeared in 15 minutes between the sides of the pot and the earth, which had been moderately pressed down. On a third occasion three large worms and a small one were placed on loose mould well mixed with fine sand and firmly pressed down, and they all disappeared, except the tail of one, in 35 minutes. On a fourth occasion six large worms were placed on argillaceous mud mixed with sand firmly pressed down, and they disappeared, except the extreme tips of the tails of two of them, in 40 minutes. In none of these cases, did the worms swallow, as far as could be seen, any earth. They generally entered the ground close to the sides of the pot.

A pot was next filled with very fine ferruginous sand, which was pressed down, well watered, and thus rendered extremely compact. A large worm left on the surface did not succeed in penetrating it for some hours, and did not bury itself completely until 25 hrs. 40 min. had elapsed. This was effected by the sand being swallowed, as was evident by the large quantity ejected from the vent, long before the whole body had disappeared. Castings of a similar nature continued to be ejected from the burrow during the whole of the following day.

As doubts have been expressed by some writers whether worms ever swallow earth solely for the sake of making their burrows, some additional cases may be given. A mass of fine reddish sand, 23 inches in thickness, left on the ground for nearly two years, had been penetrated in many places by worms; and their castings consisted partly of the reddish sand and partly of black earth brought up from beneath the mass. This sand had been dug up from a considerable depth, and was of so poor a nature that weeds could not grow on it. It is therefore highly improbable that it should have been swallowed by the worms as food. Again in a field near my house the castings frequently consist of almost pure chalk, which lies at only a little depth beneath the surface; and here again it is very improbable that the chalk should have been swallowed for the sake of the very little organic matter which could have percolated into it from the poor overlying pasture. Lastly, a casting thrown up through the concrete and decayed mortar between the tiles, with which the now ruined aisle of Beaulieu Abbey had formerly been paved, was washed, so that the coarser matter alone was left. This consisted of grains of quartz, micaceous slate, other rocks, and bricks or tiles, many of them from 1/20 to 1/10 inch in diameter. No one will suppose that these grains were swallowed as food, yet they formed more than half of the casting, for they weighed 19 grains, the whole casting having weighed 33 grains. Whenever a worm burrows to a depth of some feet in undisturbed compact ground, it must form its passage by swallowing the earth; for it is incredible that the ground could yield on all sides to the pressure of the pharynx when pushed forwards within the worm's body.

That worms swallow a larger quantity of earth for the sake of extracting any nutritious matter which it may contain than for making their burrows, appears to me certain. But as this old belief has been doubted by so high an authority as Claparede, evidence in its favour must be given in some detail. There is no a priori improbability in such a belief, for besides other annelids, especially the Arenicola marina, which throws up such a profusion of castings on our tidal sands, and which it is believed thus subsists, there are animals belonging to the most distinct classes, which do not burrow, but habitually swallow large quantities of sand; namely, the molluscan Onchidium and many Echinoderms. {37}

If earth were swallowed only when worms deepened their burrows or made new ones, castings would be thrown up only occasionally; but in many places fresh castings may be seen every morning, and the amount of earth ejected from the same burrow on successive days is large. Yet worms do not burrow to a great depth, except when the weather is very dry or intensely cold. On my lawn the black vegetable mould or humus is only about 5 inches in thickness, and overlies light-coloured or reddish clayey soil: now when castings are thrown up in the greatest profusion, only a small proportion are light coloured, and it is incredible that the worms should daily make fresh burrows in every direction in the thin superficial layer of dark-coloured mould, unless they obtained nutriment of some kind from it. I have observed a strictly analogous case in a field near my house where bright red clay lay close beneath the surface. Again on one part of the Downs near Winchester the vegetable mould overlying the chalk was found to be only from 3 to 4 inches in thickness; and the many castings here ejected were as black as ink and did not effervesce with acids; so that the worms must have confined themselves to this thin superficial layer of mould, of which large quantities were daily swallowed. In another place at no great distance the castings were white; and why the worms should have burrowed into the chalk in some places and not in others, I am unable to conjecture.

Two great piles of leaves had been left to decay in my grounds, and months after their removal, the bare surface, several yards in diameter, was so thickly covered during several months with castings that they formed an almost continuous layer; and the large number of worms which lived here must have subsisted during these months on nutritious matter contained in the black earth.

The lowest layer from another pile of decayed leaves mixed with some earth was examined under a high power, and the number of spores of various shapes and sizes which it contained was astonishingly great; and these crushed in the gizzards of worms may largely aid in supporting them. Whenever castings are thrown up in the greatest number, few or no leaves are drawn into the burrows; for instance the turf along a hedgerow, about 200 yards in length, was daily observed in the autumn during several weeks, and every morning many fresh castings were seen; but not a single leaf was drawn into these burrows. These castings from their blackness and from the nature of the subsoil could not have been brought up from a greater depth than 6 or 8 inches. On what could these worms have subsisted during this whole time, if not on matter contained in the black earth? On the other hand, whenever a large number of leaves are drawn into the burrows, the worms seem to subsist chiefly on them, for few earth-castings are then ejected on the surface. This difference in the behaviour of worms at different times, perhaps explains a statement by Claparede, namely, that triturated leaves and earth are always found in distinct parts of their intestines.

Worms sometimes abound in places where they can rarely or never obtain dead or living leaves; for instance, beneath the pavement in well-swept courtyards, into which leaves are only occasionally blown. My son Horace examined a house, one corner of which had subsided; and he found here in the cellar, which was extremely damp, many small worm-castings thrown up between the stones with which the cellar was paved; and in this case it is improbable that the worms could ever have obtained leaves. Mr. A. C. Horner confirms this account, as he has seen castings in the cellars of his house, which is an old one at Tonbridge.

But the best evidence, known to me, of worms subsisting for at least considerable periods of time solely on the organic matter contained in earth, is afforded by some facts communicated to me by Dr. King. Near Nice large castings abound in extraordinary numbers, so that 5 or 6 were often found within the space of a square foot. They consist of fine, pale-coloured earth, containing calcareous matter, which after having passed through the bodies of worms and being dried, coheres with considerable force. I have reason to believe that these castings had been formed by species of Perichaeta, which have been naturalized here from the East. {38} They rise like towers, with their summits often a little broader than their bases, sometimes to a height of above 3 and often to a height of 2.5 inches. The tallest of those which were measured was 3.3 inches in height and 1 inch in diameter. A small cylindrical passage runs up the centre of each tower, through which the worm ascends to eject the earth which it has swallowed, and thus to add to its height. A structure of this kind would not allow leaves being easily dragged from the surrounding ground into the burrows; and Dr. King, who looked carefully, never saw even a fragment of a leaf thus drawn in. Nor could any trace be discovered of the worms having crawled down the exterior surfaces of the towers in search of leaves; and had they done so, tracks would almost certainly have been left on the upper part whilst it remained soft. It does not, however, follow that these worms do not draw leaves into their burrows during some other season of the year, at which time they would not build up their towers.

From the several foregoing cases, it can hardly be doubted that worms swallow earth, not only for the sake of making their burrows, but for obtaining food. Hensen, however, concludes from his analyses of mould that worms probably could not live on ordinary vegetable mould, though he admits that they might be nourished to some extent by leaf-mould. {39} But we have seen that worms eagerly devour raw meat, fat, and dead worms; and ordinary mould can hardly fail to contain many ova, larvae, and small living or dead creatures, spores of cryptogamic plants, and micrococci, such as those which give rise to saltpetre. These various organisms, together with some cellulose from any leaves and roots not utterly decayed, might well account for such large quantities of mould being swallowed by worms. It may be worth while here to recall the fact that certain species of Utricularia, which grow in damp places in the tropics, possess bladders beautifully constructed for catching minute subterranean animals; and these traps would not have been developed unless many small animals inhabited such soil.

The depth to which worms penetrate, and the construction of their burrows.--Although worms usually live near the surface, yet they burrow to a considerable depth during long-continued dry weather and severe cold. In Scandinavia, according to Eisen, and in Scotland, according to Mr. Lindsay Carnagie, the burrows run down to a depth of from 7 to 8 feet; in North Germany, according to Hoffmeister, from 6 to 8 feet, but Hensen says, from 3 to 6 feet. This latter observer has seen worms frozen at a depth of 1.5 feet beneath the surface. I have not myself had many opportunities for observation, but I have often met with worms at depths of 3 to 4 feet. In a bed of fine sand overlying the chalk, which had never been disturbed, a worm was cut into two at 55 inches, and another was found here at Down in December at the bottom of its burrow, at 61 inches beneath the surface. Lastly, in earth near an old Roman Villa, which had not been disturbed for many centuries, a worm was met with at a depth of 66 inches; and this was in the middle of August.

The burrows run down perpendicularly, or more commonly a little obliquely. They are said sometimes to branch, but as far as I have seen this does not occur, except in recently dug ground and near the surface. They are generally, or as I believe invariably, lined with a thin layer of fine, dark-coloured earth voided by the worms; so that they must at first be made a little wider than their ultimate diameter. I have seen several burrows in undisturbed sand thus lined at a depth of 4 ft. 6 in.; and others close to the surface thus lined in recently dug ground. The walls of fresh burrows are often dotted with little globular pellets of voided earth, still soft and viscid; and these, as it appears, are spread out on all sides by the worm as it travels up or down its burrow. The lining thus formed becomes very compact and smooth when nearly dry, and closely fits the worm's body. The minute reflexed bristles which project in rows on all sides from the body, thus have excellent points of support; and the burrow is rendered well adapted for the rapid movement of the animal. The lining appears also to strengthen the walls, and perhaps saves the worm's body from being scratched. I think so because several burrows which passed through a layer of sifted coal-cinders, spread over turf to a thickness of 1.5 inch, had been thus lined to an unusual thickness. In this case the worms, judging from the castings, had pushed the cinders away on all sides and had not swallowed any of them. In another place, burrows similarly lined, passed through a layer of coarse coal-cinders, 3.5 inches in thickness. We thus see that the burrows are not mere excavations, but may rather be compared with tunnels lined with cement.

The mouths of the burrow are in addition often lined with leaves; and this is an instinct distinct from that of plugging them up, and does not appear to have been hitherto noticed. Many leaves of the Scotch-fir or pine (Pinus sylvestris) were given to worms kept in confinement in two pots; and when after several weeks the earth was carefully broken up, the upper parts of three oblique burrows were found surrounded for lengths of 7, 4, and 3.5 inches with pine- leaves, together with fragments of other leaves which had been given the worms as food. Glass beads and bits of tile, which had been strewed on the surface of the soil, were stuck into the interstices between the pine-leaves; and these interstices were likewise plastered with the viscid castings voided by the worms. The structures thus formed cohered so well, that I succeeded in removing one with only a little earth adhering to it. It consisted of a slightly curved cylindrical case, the interior of which could be seen through holes in the sides and at either end. The pine- leaves had all been drawn in by their bases; and the sharp points of the needles had been pressed into the lining of voided earth. Had this not been effectually done, the sharp points would have prevented the retreat of the worms into their burrows; and these structures would have resembled traps armed with converging points of wire, rendering the ingress of an animal easy and its egress difficult or impossible. The skill shown by these worms is noteworthy and is the more remarkable, as the Scotch pine is not a native of this district.

After having examined these burrows made by worms in confinement, I looked at those in a flower-bed near some Scotch pines. These had all been plugged up in the ordinary manner with the leaves of this tree, drawn in for a length of from 1 to 1.5 inch; but the mouths of many of them were likewise lined with them, mingled with fragments of other kinds of leaves, drawn in to a depth of 4 or 5 inches. Worms often remain, as formerly stated, for a long time close to the mouths of their burrows, apparently for warmth; and the basket-like structures formed of leaves would keep their bodies from coming into close contact with the cold damp earth. That they habitually rested on the pine-leaves, was rendered probable by their clean and almost polished surfaces.

The burrows which run far down into the ground, generally, or at least often, terminate in a little enlargement or chamber. Here, according to Hoffmeister, one or several worms pass the winter rolled up into a ball. Mr. Lindsay Carnagie informed me (1838) that he had examined many burrows over a stone-quarry in Scotland, where the overlying boulder-clay and mould had recently been cleared away, and a little vertical cliff thus left. In several cases the same burrow was a little enlarged at two or three points one beneath the other; and all the burrows terminated in a rather large chamber, at a depth of 7 or 8 feet from the surface. These chambers contained many small sharp bits of stone and husks of flax-seeds. They must also have contained living seeds, for on the following spring Mr. Carnagie saw grass-plants sprouting out of some of the intersected chambers. I found at Abinger in Surrey two burrows terminating in similar chambers at a depth of 36 and 41 inches, and these were lined or paved with little pebbles, about as large as mustard seeds; and in one of the chambers there was a decayed oat-grain, with its husk. Hensen likewise states that the bottoms of the burrows are lined with little stones; and where these could not be procured, seeds, apparently of the pear, had been used, as many as fifteen having been carried down into a single burrow, one of which had germinated. {40} We thus see how easily a botanist might be deceived who wished to learn how long deeply buried seeds remained alive, if he were to collect earth from a considerable depth, on the supposition that it could contain only seeds which had long lain buried. It is probable that the little stones, as well as the seeds, are carried down from the surface by being swallowed; for a surprising number of glass beads, bits of tile and of glass were certainly thus carried down by worms kept in pots; but some may have been carried down within their mouths. The sole conjecture which I can form why worms line their winter-quarters with little stones and seeds, is to prevent their closely coiled-up bodies from coming into close contact with the surrounding cold soil; and such contact would perhaps interfere with their respiration which is effected by the skin alone.

A worm after swallowing earth, whether for making its burrow or for food, soon comes to the surface to empty its body. The ejected earth is thoroughly mingled with the intestinal secretions, and is thus rendered viscid. After being dried it sets hard. I have watched worms during the act of ejection, and when the earth was in a very liquid state it was ejected in little spurts, and by a slow peristaltic movement when not so liquid. It is not cast indifferently on any side, but with some care, first on one and then on another side; the tail being used almost like a trowel. When a worm comes to the surface to eject earth, the tail protrudes, but when it collects leaves its head must protrude. Worms therefore must have the power of turning round in their closely-fitting burrows; and this, as it appears to us, would be a difficult feat. As soon as a little heap has been formed, the worm apparently avoids, for the sake of safety, protruding its tail; and the earthy matter is forced up through the previously deposited soft mass. The mouth of the same burrow is used for this purpose for a considerable time. In the case of the tower-like castings (see Fig. 2) near Nice, and of the similar but still taller towers from Bengal (hereafter to be described and figured), a considerable degree of skill is exhibited in their construction. Dr. King also observed that the passage up these towers hardly ever ran in the same exact line with the underlying burrow, so that a thin cylindrical object such as a haulm of grass, could not be passed down the tower into the burrow; and this change of direction probably serves in some manner as a protection.

Worms do not always eject their castings on the surface of the ground. When they can find any cavity, as when burrowing in newly turned-up earth, or between the stems of banked-up plants, they deposit their castings in such places. So again any hollow beneath a large stone lying on the surface of the ground, is soon filled up with their castings. According to Hensen, old burrows are habitually used for this purpose; but as far as my experience serves, this is not the case, excepting with those near the surface in recently dug ground. I think that Hensen may have been deceived by the walls of old burrows, lined with black earth, having sunk in or collapsed; for black streaks are thus left, and these are conspicuous when passing through light-coloured soil, and might be mistaken for completely filled-up burrows.

It is certain that old burrows collapse in the course of time; for as we shall see in the next chapter, the fine earth voided by worms, if spread out uniformly, would form in many places in the course of a year a layer 0.2 of an inch in thickness; so that at any rate this large amount is not deposited within the old unused burrows. If the burrows did not collapse, the whole ground would be first thickly riddled with holes to a depth of about ten inches, and in fifty years a hollow unsupported space, ten inches in depth, would be left. The holes left by the decay of successively formed roots of trees and plants must likewise collapse in the course of time.

The burrows of worms run down perpendicularly or a little obliquely, and where the soil is at all argillaceous, there is no difficulty in believing that the walls would slowly flow or slide inwards during very wet weather. When, however, the soil is sandy or mingled with many small stones, it can hardly be viscous enough to flow inwards during even the wettest weather; but another agency may here come into play. After much rain the ground swells, and as it cannot expand laterally, the surface rises; during dry weather it sinks again. For instance, a large flat stone laid on the surface of a field sank 3.33 mm. whilst the weather was dry between May 9th and June 13th, and rose 1.91 mm, between September 7th and 19th of the same year, much rain having fallen during the latter part of this time. During frosts and thaws the movements were twice as great. These observations were made by my son Horace, who will hereafter publish an account of the movements of this stone during successive wet and dry seasons, and of the effects of its being undermined by worms. Now when the ground swells, if it be penetrated by cylindrical holes, such as worm-burrows, their walls will tend to yield and be pressed inwards; and the yielding will be greater in the deeper parts (supposing the whole to be equally moistened) from the greater weight of the superincumbent soil which has to be raised, than in the parts near the surface. When the ground dries, the walls will shrink a little and the burrows will be a little enlarged. Their enlargement, however, through the lateral contraction of the ground, will not be favoured, but rather opposed, by the weight of the superincumbent soil.

Distribution of Worms.--Earth-worms are found in all parts of the world, and some of the genera have an enormous range. {41} They inhabit the most isolated islands; they abound in Iceland, and are known to exist in the West Indies, St. Helena, Madagascar, New Caledonia and Tahiti. In the Antarctic regions, worms from Kerguelen Land have been described by Ray Lankester; and I found them in the Falkland Islands. How they reach such isolated islands is at present quite unknown. They are easily killed by salt-water, and it does not appear probable that young worms or their egg- capsules could be carried in earth adhering to the feet or beaks of land-birds. Moreover Kerguelen Land is not now inhabited by any land-bird.

In this volume we are chiefly concerned with the earth cast up by worms, and I have gleaned a few facts on this subject with respect to distant lands. Worms throw up plenty of castings in the United States. In Venezuela, castings, probably ejected by species of Urochaeta, are common in the gardens and fields, but not in the forests, as I hear from Dr. Ernst of Caracas. He collected 156 castings from the court-yard of his house, having an area of 200 square yards. They varied in bulk from half a cubic centimeter to five cubic centimeters, and were on an average three cubic centimeters. They were, therefore, of small size in comparison with those often found in England; for six large castings from a field near my house averaged 16 cubic centimeters. Several species of earth-worms are common in St. Catharina in South Brazil, and Fritz Muller informs me "that in most parts of the forests and pasture-lands, the whole soil, to a depth of a quarter of a metre, looks as if it had passed repeatedly through the intestines of earth-worms, even where hardly any castings are to be seen on the surface." A gigantic but very rare species is found there, the burrows of which are sometimes even two centimeters or nearly 0.8 of an inch in diameter, and which apparently penetrate the ground to a great depth.

In the dry climate of New South Wales, I hardly expected that worms would be common; but Dr. G. Krefft of Sydney, to whom I applied, after making inquiries from gardeners and others, and from his own observations, informs me that their castings abound. He sent me some collected after heavy rain, and they consisted of little pellets, about 0.15 inch in diameter; and the blackened sandy earth of which they were formed still cohered with considerable tenacity.

The late Mr. John Scott of the Botanic Gardens near Calcutta made many observations for me on worms living under the hot and humid climate of Bengal. The castings abound almost everywhere, in jungles and in the open ground, to a greater degree, as he thinks, than in England. After the water has subsided from the flooded rice-fields, the whole surface very soon becomes studded with castings--a fact which much surprised Mr. Scott, as he did not know how long worms could survive beneath water. They cause much trouble in the Botanic garden, "for some of the finest of our lawns can be kept in anything like order only by being almost daily rolled; if left undisturbed for a few days they become studded with large castings." These closely resemble those described as abounding near Nice; and they are probably the work of a species of Perichaeta. They stand up like towers, with an open passage in the centre.

A figure of one of these castings from a photograph is here given (Fig. 3). The largest received by me was 3.5 inches in height and 1.35 inch in diameter; another was only 0.75 inch in diameter and 2.75 in height. In the following year, Mr. Scott measured several of the largest; one was 6 inches in height and nearly 1.5 in diameter: two others were 5 inches in height and respectively 2 and rather more than 2.5 inches in diameter. The average weight of the 22 castings sent to me was 35 grammes (1.25 oz.); and one of them weighed 44.8 grammes (or 2 oz.). All these castings were thrown up either in one night or in two. Where the ground in Bengal is dry, as under large trees, castings of a different kind are found in vast numbers: these consist of little oval or conical bodies, from about the 1/20 to rather above 1/10 of an inch in length. They are obviously voided by a distinct species of worms.

The period during which worms near Calcutta display such extraordinary activity lasts for only a little over two months, namely, during the cool season after the rains. At this time they are generally found within about 10 inches beneath the surface. During the hot season they burrow to a greater depth, and are then found coiled up and apparently hybernating. Mr. Scott has never seen them at a greater depth than 2.5 feet, but has heard of their having been found at 4 feet. Within the forests, fresh castings may be found even during the hot season. The worms in the Botanic garden, during the cool and dry season, draw many leaves and little sticks into the mouths of their burrows, like our English worms; but they rarely act in this manner during the rainy season.

Mr. Scott saw worm-castings on the lofty mountains of Sikkim in North India. In South India Dr. King found in one place, on the plateau of the Nilgiris, at an elevation of 7000 feet, "a good many castings," which are interesting for their great size. The worms which eject them are seen only during the wet season, and are reported to be from 12 to 15 inches in length, and as thick as a man's little finger. These castings were collected by Dr. King after a period of 110 days without any rain; and they must have been ejected either during the north-east or more probably during the previous south-west monsoon; for their surfaces had suffered some disintegration and they were penetrated by many fine roots. A drawing is here given (Fig. 4) of one which seems to have best retained its original size and appearance. Notwithstanding some loss from disintegration, five of the largest of these castings (after having been well sun-dried) weighed each on an average 89.5 grammes, or above 3 oz.; and the largest weighed 123.14 grammes, or 4.33 oz.,--that is, above a quarter of a pound! The largest convolutions were rather more than one inch in diameter; but it is probable that they had subsided a little whilst soft, and that their diameters had thus been increased. Some had flowed so much that they now consisted of a pile of almost flat confluent cakes. All were formed of fine, rather light-coloured earth, and were surprisingly hard and compact, owing no doubt to the animal matter by which the particles of earth had been cemented together. They did not disintegrate, even when left for some hours in water. Although they had been cast up on the surface of gravelly soil, they contained extremely few bits of rock, the largest of which was only 0.15 inch in diameter.

Dr. King saw in Ceylon a worm about 2 feet in length and 0.5 inch in diameter; and he was told that it was a very common species during the wet season. These worms must throw up castings at least as large as those on the Nilgiri Mountains; but Dr. King saw none during his short visit to Ceylon.

Sufficient facts have now been given, showing that worms do much work in bringing up fine earth to the surface in most or all parts of the world, and under the most different climates.


{28} Claparede remarks ('Zeitschrift fur wisseuschaft. Zoolog.' B. 19, 1869, p. 602) that the pharynx appears from its structure to be adapted for suction.

{29} An account of her observations is given in the 'Gardeners' Chronicle,' March 28th, 1868, p. 324.

{30} London's 'Gard. Mag.' xvii. p. 216, as quoted in the 'Catalogue of the British Museum Worms,' 1865, p. 327.

{31} 'Familie der Regenwurmer,' p. 19.

{32} In these narrow triangles the apical angle is 9 degrees 34 seconds, and the basal angles 85 degrees 13 seconds. In the broader triangles the apical angle is 19 degrees 10 seconds and the basal angles 80 degrees 25 seconds.

{33} See his interesting work, 'Souvenirs entomologiques,' 1879, pp. 168-177.

{34} Mobius, 'Die Bewegungen der Thiere,' &c., 1873, p. 111.

{35} 'Annals and Mag. of N. History,' series ii. vol. ix. 1852, p. 333.

{36} 'Archives de Zoolog. exper.' tom. iii. 1874, p. 405.

{37} I state this on the authority of Semper, 'Reisen im Archipel der Philippinen,' Th. ii. 1877, p. 30.

{38} Dr. King gave me some worms collected near Nice, which, as he believes, had constructed these castings. They were sent to M. Perrier, who with great kindness examined and named them for me: they consisted of Perichaeta affinis, a native of Cochin China and of the Philippines; P. Luzonica, a native of Luzon in the Philippines; and P. Houlleti, which lives near Calcutta. M. Perrier informs me that species of Perichaeta have been naturalized in the gardens near Montpellier and in Algiers. Before I had any reason to suspect that the tower-like castings from Nice had been formed by worms not endemic in the country, I was greatly surprised to see how closely they resembled castings sent to me from near Calcutta, where it is known that species of Perichaeta abound.

{39} 'Zeitschrift fur wissenschaft. Zoolog.' B. xxviii. 1877, p. 364.

{40} 'Zeitschrift fur wissenschaft. Zoolog.' B. xxviii. 1877, p. 356.

{41} Perrier, 'Archives de Zoolog. exper.' tom. 3, p. 378, 1874.


Charles Darwin

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