[B0]

[page in Darwin's hand]

Chapter I.

The Habits of Earth-Worms.

Nature of the sites inhabited  —  Can live long under water — Nocturnal — W&er about at night — Often lie close to the mouths of their burrows, & are thus destroyed in large numbers by birds — Structure — Do not possess eyes, but can distinguish between light & darkness — Retreat rapidly when brightly illuminated, not by a reflex action — Power of attention — Sensitive to heat & cold — Completely deaf — Sensitive to vibrations & to touch — Feeble power of smell — Taste — Mental qualities — Nature of food — Omnivorous — Digestion — Leaves before being swallowed, moistened with a fluid of the nature of the pancreatic secretion — Extra-stomachal digestion — Calciferous gl&s, structure of — Calcareous concretions formed in the anterior pair of glands — The calcareous matter primarily an excretion, but secondarily serves to neutralise the acids generated during the digestive process.

1

Hill

Chapter. I

Habits of worms

Earth-worms (Oligcheta terricola) are distributed throughout the world under the form of a few genera, which externally are closely similar to one another. The British species of Lumbricus have never been carefully monographed; but we may judge of their probable number from those inhabiting neighbouring countries. In Scandinavia there are eight species, according to Eisen;* but two of these rarely burrow in the ground, and one inhabits very wet places or even lives under the water. We are here concerned only with the kinds which bring up earth to the surface in the form of castings. Hoffmeister says that the species in Germany are not well known, but gives the same number as Eisen, together with some strongly marked varieties.†

* 'Bidrag till Skandinaviens Oligochætfauna,' 1871.

† 'Die bis jetzt bekannten Arten aus der Familie der Regenwürmer,' 1845.

(2

[page in Darwin's hand]

(Earth-worms abound in England in many different stations. Their castings may be seen in extraordinary numbers on commons and chalk-downs, so as almost to cover the whole surface, where the soil is poor and the grass short and thin. But they are almost or quite as numerous in some of the London parks, where the grass grows well and the soil appears rich. Even on the same field worms are much more frequent in some places than in others, without any visible difference in the nature of the soil. They abound in paved court-yards close to houses; and an instance will be given in which they had burrowed through the floor of a very damp cellar. I have seen worms in black peat in a boggy field; but they are extremely rare, or quite absent in the drier, brown, fibrous peat, which is so much valued by gardeners. On dry, sandy or gravelly tracks, where heath with some gorse, ferns, coarse grass, moss and lichens alone grow, hardly any worms can be found. But in many parts of England, wherever a path crosses a heath, its surface becomes covered with a fine short sward. Whether this change of

(3

[page in Darwin's hand]

vegetation is due to the taller plants being killed by the occasional trampling of man and animals, or to the soil being occasionally manured by the droppings from animals, I do not know.* On such grassy paths worm-castings may often be seen. On a heath in Surrey, which was carefully examined, there were only a few castings on these paths, where they were much inclined; but on the more level parts, where a bed of fine earth had been washed down from the steeper parts and had accumulated to a thickness of a few inches, worm-castings abounded. These spots seemed to be overstocked with worms, so that they had been compelled to spread to a distance of a few feet from the grassy paths, and here their castings had been thrown up among the heath; but beyond this limit, not a single casting could be found. A layer, though a thin one, of fine earth, which probably long retains some moisture, is in all cases, as I believe, necessary for their existence; and the mere compression of the soil appears to be in some degree favourable to them, for they often abound in old gravel walks, and in foot-paths across fields.)

[3V]

[page in Darwin's hand]

Foot-note.

*(a). There is even some reason to believe that pressure is actually favourable to the growth of grasses, for Professor Buckman, who made many observations on their growth in the experimental gardens of the Royal Agricultural College, remarks ('Gardeners' Chronicle,' 1854, p. 619): "Another circumstance in the cultivation of grasses in the separate form or small patches, is the impossibility of rolling or treading them firmly, without which no pasture can continue good."

(4

[page in Darwin's hand]

Ch I

(Beneath large trees few castings can be found during certain seasons of the year, and this is apparently due to the moisture having been sucked out of the ground by the innumerable roots of the trees; for such places may be seen covered with castings after the heavy autumnal rains. Although most coppices and woods support many worms, yet in a forest of tall and ancient beech-trees in Knole Park, where the ground beneath was bare of all vegetation, not a single casting could be found over wide spaces, even during the autumn. Nevertheless, castings were abundant on some grass-covered glades and indentations which penetrated this forest. On the mountains of North Wales and on the Alps, worms, as I have been informed, are in most places rare; and this may perhaps be due to the close proximity of the subjacent rocks, into which worms cannot burrow during the winter so as to escape being frozen. Dr. McIntosh, however, found worm-castings at a height of 1500 feet on Schiehallion in Scotland. They are numerous on some hills near Turin at from 2000 to 3000

(5

[page in Darwin's hand]

Ch I

feet above the sea, and at a great altitude on the Nilgiri Mountains in South India and on the Himalaya.

(Earth-worms must be considered as terrestrial animals, though they are still in one sense semi-aquatic, like the other members of the great class of annelids to which they belong. M. Perrier found that their exposure to the dry air of a room for only a single night was fatal to them. On the other hand he kept several large worms alive for nearly four months, completely submerged in water.*  * I shall have occasion often to refer to M. Perrier's admirable memoir, 'Organisation des Lombriciens terrestres' in 'Archives de Zoolog. expér.' tom. iii. 1874, p. 372. C. F. Morren ('De Lumbrici terrestris,' 1829, p. 14) found that worms endured immersion for fifteen to twenty days in summer, but that in winter they died when thus treated.

During the summer when the ground is dry, they penetrate to a considerable depth and cease to work, as they do during the winter when the ground is frozen. Worms are nocturnal in their habits, and at night may be seen crawling about

in large numbers, but usually with their tails still inserted in their burrows. By the expansion of this part of their bodies, assisted by the short bristles directed slightly backwards with which their bodies are armed, they hold so fast that

(6

[page in Darwin's hand]

Ch I.

they can seldom be dragged out of the ground without being torn into pieces.*  (* Morren, 'De Lumbrici terrestris,' &c., 1829, p. 67.

All observers agree that they   During the day they remain in their burrows, except at the pairing season, when those which inhabit adjoining burrows expose the greater part of their bodies for an hour or two in the early morning. Sick individuals, which are generally affected by the parasitic larvæ of a fly, must also be excepted, as they wander about during the day and die on the surface. After heavy rain succeeding dry weather, an astonishing number of dead worms may sometimes be seen lying on the ground. Mr. Galton informs me that on one such occasion (March, 1881), the dead worms averaged one for every two and a half paces in length on a walk in Hyde Park, four paces in width. He counted no less than 45 dead worms in one place in a length of sixteen paces. From the facts above given, it is not probable that these worms could have been drowned, and if they had been drowned they would have perished in their burrows. I believe that they were already sick, and that their deaths were hastened by the unfavourable conditions.)

(6A

[page in Darwin's hand]

Ch. I

Lurer

It has often been said that under ordinary circumstances healthy

 

worms never, or very rarely, completely leave their burrows at night; but this is an error, as White of Selborne long ago knew. In the morning, after there has been heavy rain, the film of mud or of very fine sand over gravel-walks is often plainly marked with their tracks. I have noticed this from August to May, both months included, and it probably occurs during the two remaining months of the year when they are wet. On these occasions, very few dead worms could anywhere be seen. On January 31, 1881, after a long-continued and unusually severe frost with much snow, as soon as a thaw set in, the walks were marked with innumerable tracks. On one occasion, five tracks were counted crossing a space of only an inch square. They could

(7

[page in Darwin's hand]

Ch. I

 

sometimes be traced either to or from the mouths of the burrows in the gravel-walks, for distances between 2 or 3 up to 15 yards. I have never seen two tracks leading to the same burrow; nor is it likely, from what we shall presently see of their sense-organs, that a worm could find its way back to its burrow after having once left it. They apparently leave their burrows on a voyage of discovery, and thus they find new sites to inhabit.)

(Morren states* (* 'De Lumbrici terrestris,' &c., p. 14.)  that worms often lie for hours almost motionless close beneath the mouths of their burrows. I have occasionally noticed the same fact with worms kept in pots in the house; so that by looking down into their burrows, their heads could just be seen. If the ejected earth or rubbish over the burrows be suddenly removed, the end of the worm's body may very often be seen rapidly retreating. This habit of lying near the surface leads to their destruction to an immense extent. Every morning during certain seasons of the year, the thrushes and blackbirds on every lawn throughout the country draw out of their holes    without any digging  an astonishing number of worms; and this they could not do, unless the wroms exhibited their heads within their burrows just beneath the surface.

8

[page in Emma Darwin's hand]

Ch I

It is not probable that worms behave in this manner for the sake of breathing fresh air, for we have seen that they can live for a long time under water. I believe that they lie near the surface for the sake of warmth, especially in the morning; and we shall hereafter find that they often coat the mouths of their burrows with leaves, apparently to prevent their bodies from coming into close contact with the cold damp earth. It is said that they completely close their burrows during the winter.

Structure.— A few remarks must be made on this subject. The body of a large worm consists of from 100 to 200 almost cylindrical rings or segments, each furnished with minute bristles. The muscular system is well developed. Worms can crawl backwards as well as forwards, and by the aid of their affixed tails can retreat with astonishing  extraordinary rapidity into their

[8v]

8

Ch I

For they are do not dig them up

[8V]

Fig. I (not Roman fig)

[proof of Fig. 1] Mouth.

Pharnyx.

Œsophagus.

Calciferous glands.

Œsophagus.

Crop.

Gizzard.

Upper part of intestine.

Diagram of the alimentary canal of an earthworm (Lumbricus), copied from Ray Lankester in Quart. Journ. of Microscop. Soc. vol. iv. N.S. Pl. vii. —

((cut back close to right & put names of Parts in small type)

9

[page in Emma Darwin's hand]

Ch I

 

burrows. The mouth is situated at the anterior end of the body, and is provided with a little projection (lobe or lip, as it has been variously called) which is used for prehension. Internally, behind the mouth, there is a strong pharynx, shown in the accompanying diagram (Fig. 1) which is pushed forwards when the animal eats, and this part corresponds, according to Perrier, with the protrudable trunk or proboscis of other annelids. The pharynx leads into the œsophagus, on each side of which in the lower part there are three pairs of large glands, which secrete a surprising amount of carbonate of lime. These calciferous glands are highly remarkable, for nothing like them is known in any other animal. Their use will be discussed when we treat of the digestive process. In most of the species, the œsophagus is enlarged into a crop in front of the gizzard. This latter organ is lined with a smooth thick

10

[page in Emma Darwin's hand]

Ch I

chitinous membrane, and is surrounded by weak longitudinal, but by powerful transverse muscles. Perrier saw these muscles in energetic action; and, as he remarks, the trituration of the food must be chiefly effected by this organ, for worms possess no jaws or teeth of any kind. Grains of sand and small stones, from the 1/20 to a little more than the 1/10 inch in diameter, may generally be found in their gizzards and intestines. As it is certain that worms swallow many little stones, independently of those swallowed while excavating their burrows, it is probable that they serve, like mill-stones, to triturate their food. The gizzard opens into the intestine, which runs in a straight course to the vent at the posterior end of the body. The intestine presents a remarkable structure, the typhosolis, or, as the old anatomists called it, an intestine within an intestine; and Claparède* has shown that this consists of a deep

[10V]

*(a) Histolog. Untersuchungen über die Regenwürmer. 'Zeitschrift für wissenschaft. Zoologie,' B. xix., 1869, p. 611.

11

[page in Emma Darwin's hand]

Ch I

longitudinal involution of the walls of the intestine, by which means an extensive absorbent surface is gained.)

(The circulatory system is well developed. Worms breathe by their skin, as they do not possess any special respiratory organs. The two sexes are united in the same individual, but two individuals pair together. The nervous system is fairly well developed; and the two almost confluent cerebral ganglia are situated very near to the anterior end of the body.

(Sense organs.— Worms are destitute of eyes, and at first I thought that they were quite insensible to light; for those kept in confinement were repeatedly observed by the aid of a candle, and others out of doors by the aid of a lantern, yet they were rarely alarmed, although extremely timid animals. Other persons have found no difficulty in observing worms at night by the same means.*

Hoffmeister, however, states† that worms, with the exception of a few individuals,

[11V]

* For instance, Mr. Bridgman and Mr. Newman ('The Zoologist,' vol. vii. 1849, p. 2576), and some friends who observed worms for me.

† 'Familie der Regenwürmer,' 1845, p. 18.

12

[page in Emma Darwin's hand]

Ch I

are extremely sensitive to light; but he admits that in most cases a certain time is requisite for its action. These statements led me to watch on many successive nights worms kept in pots, which were protected from currents of air by means of glass plates. The pots were approached very gently, in order that no vibration of the floor should be caused. When under these circumstances worms were illuminated by a bull's-eye lantern having slides of dark red and blue glass, which intercepted so much light that they could be seen only with some difficulty, they were not at all affected by this amount of light, however long they were exposed to it. The light, as far as I could judge, was brighter than that from the full moon. Its colour apparently made no difference in the result. When they were illuminated by a candle, or even by a bright paraffin lamp, they were not usually affected at first. Nor were they when the light was alternately admitted and shut off. Sometimes, however, they behaved very differently, for as

13

[page in Emma Darwin's hand]

Ch I

soon as the light fell on them, they withdrew into their burrows with almost instantaneous rapidity. This occurred perhaps once out of a dozen times. When they did not withdraw instantly, they often raised the anterior tapering ends of their bodies from the ground, as if their attention was aroused or as if surprise was felt; or they moved their bodies from side to side as if feeling for some object. They appeared distressed by the light; but I doubt whether this was really the case, for on two occasions after withdrawing slowly, they remained for a long time with their anterior extremities protruding a little from the mouths of their burrows, in which position they were ready for instant and complete withdrawal.

When the light from a candle was concentrated by means of a large lens on the anterior extremity, they generally withdrew instantly; but this concentrated light failed to act perhaps once out of half a dozen trials. The light was on one occasion concentrated on a worm lying beneath water in a saucer,

14

[page in Emma Darwin's hand]

Ch I

and it instantly withdrew into its burrow. In all cases the duration of the light, unless extremely feeble, made a great difference in the result; for worms left exposed before a paraffin lamp or a candle invariably retreated into their burrows within from five to fifteen minutes; and if in the evening the pots were illuminated before the worms had come out of their burrows, they failed to appear.

From the foregoing facts it is evident that light affects worms by its intensity and by its duration. It is only the anterior extremity of the body, where the cerebral ganglia lie, which is affected by light, as Hoffmeister asserts, and as I observed on many occasions. If this part is shaded, other parts of the body may be fully illuminated, and no effect will be produced. As these animals have no eyes, we must suppose that the light passes through their skins, and in some manner excites their cerebral ganglia. It appeared at first probable that the different manner in which they were affected at different

15

[page in Emma Darwin's hand]

Ch I

times 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 of the animal, as if it were an automaton.

16

[page in Emma Darwin's hand]

Ch I

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 object 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

17

[page in Emma Darwin's hand]

Ch I

far-fetched; for we thus attribute to the worm attention and some mental power, nevertheless 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 window, remained during the day-time in their burrows and came out every night; and they continued thus to act for a week. No doubt a little light 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. I judge of this from

18

[page in Emma Darwin's hand]

Ch I

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 notice; a second withdrew 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 temperature, 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 repeatedly 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 undulations in the

19

[page in Emma Darwin's hand]

Ch I

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 pots in which they lived, or the table

20

[page in Emma Darwin's hand]

Ch I

on which the pot stood, was accidentally and lightly struck; but they appeared less sensitive 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 ground 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

21

[page in Emma Darwin's hand]

Ch I

Glass-plates. When a worm first comes out of its burrow, it generally moves the much extended 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.

[21v]

[page in Darwin's hand]

This was tried because it appeared possible that [illeg] they [several words illeg] enemy.

22

[page in Emma Darwin's hand]

Ch I

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 ¼ of an inch of common garden soil; and they were always discovered by the worms. One bit of cabbage was discovered 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

23

[page in Emma Darwin's hand]

Ch I

the 7th  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 discovered within 48 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 onion had been removed, I looked beneath them to see whether the worms had accidentally 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

24

[page in Emma Darwin's hand]

Ch I

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 removed after the second night. These several facts indicate that worms possess some power of smell; and that they discover by this means odoriferous and much-coveted kinds of food.)

(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 distinguish 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

25

[page in Emma Darwin's hand]

Ch I

pickling were given them, and they preferred the green, the red being either wholly neglected or much less gnawed. On two other occasions, however, 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 manifest after many trials that wild cherry leaves were greatly preferred to those of the lime-tree and hazel (Corylus). According to Mr. Bridgman

26

[page in Emma Darwin's hand]

Ch I

the half-decayed leaves of Phlox verna are particularly liked by worms.* *'The Zoologist,' vol. vii. 1849, p. 2576.   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 occasionally 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 by 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

27

[page in Emma Darwin's hand]

Ch I

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.* * 'Familie der Regenwürmer,' p.  13.   Although worms are so remarkably deficient in the several sense-organs, this does not necessarily preclude intelligence, as we know from such cases as those of Laura Bridgman; and we have seen that when their attention is engaged, they neglect impressions to

[27 repeated]

28

[page in Emma Darwin's hand]

Ch I

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 Perichæta eject their castings, so as to construct towers; also by the manner in which the burrows of the common earth-worm are smoothly lined with fine earth and often with little stones, and the mouths of their burrows with leaves. One of their strongest instincts is the plugging up the mouths of their burrows with various objects; and very young worms act in this manner. But some degree of intelligence appears, as we shall see in the next chapter, to be exhibited in this work,—a result which has surprised me more than anything else in regard to worms.)

29

[page in Emma Darwin's hand]

Howlett

Ch I

Food and Digestion.— Worms are omnivorous. They swallow an enormous quantity of earth, out of which they extract any digestible matter which it may contain; but to this subject I must recur. They also consume a large number of half-decayed leaves of all kinds, excepting a few which have an unpleasant taste or are too tough for them; likewise petioles, peduncles and decayed flowers. But they will also consume fresh leaves, as I have found by repeated trials. According to Morren*  * 'De Lumbrici terrestris' p. 19.   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 con-

30

[page in Emma Darwin's hand]

Ch I

sumed. Raw fat seems to be preferred even to raw meat or to any other substance which was given them, and much was consumed. They are cannibals, for the two halves of a dead worm placed in two of the pots were dragged into the burrows and gnawed; but as far a I could judge, they prefer fresh to putrid meat, and in so far I differ from Hoffmeister.

Léon Frédéricq states* * 'Archives de Zoologie expérimentale,' tom. vii. 1878, p. 394.  that the digestive fluid of worms is of the same nature as the pancreatic secretion of the higher animals; and this conclusion agrees perfectly with the kinds of food which worms consume. Pancreatic juice emulsifies fat, and we have just seen how greedily worms devour fat; it dissolves fibrin, and worms eat raw meat; it converts starch into grape-sugar with wonderful rapidity, and we shall presently show that the digestive fluid of worms acts on starch.†  † On the

33

[31-32 missing]

[page in Emma Darwin's hand]

Ch I

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 transparent 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, however, merely show that the secreted fluid is highly injurious or

[33v]

[page in Darwin's hand]

(33

Ch. I

of a dark brown tint; & this change effect must have been produced in less than 12 hours.

34

[page in Emma Darwin's hand]

Ch I

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 discoloured 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 days they were affected in a 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

35

[page in Emma Darwin's hand]

Ch I

2 mm in diameter. The appearance thus presented 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 transudation 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

36

[page in Emma Darwin's hand]

Ch I

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 preserved 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,*

[36V]

* Claparède doubts whether saliva is secreted by worms: see 'Zeitschrift für wissenschaft. Zoologie,' B. xix. 1869, p. 601.

37

[page in Emma Darwin's hand]

Ch I

but pancreatic secretion; and we know from Frédéricq that a secretion of this kind is found in the intestines of worms. As the leaves which are dragged into the burrows are often dry and shrivelled, it is indispensable 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 canal. I am not aware of any other case of extra-stomachal digestion having been recorded. 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 Dionæa; for here animal matter is digested and converted into peptone not within a stomach, but on the surfaces of the leaves.)

(38

[in Darwin's hand]

Ch I

Calciferous Glands. — These glands (see Fig. 1), judging from their size and from their rich supply of blood-vessels, must be of much importance to the animal. But almost as many theories have been advanced on their use as there have been observers. They consist of three pairs, which in the common earth-worm debouch into the alimentary canal in advance of the gizzard, but posteriorly to it in Urochtæa and some other genera.*(a) The two posterior pairs are formed by lamellæ, which according to Claparède, are diverticula from the œsophagus.†(a)

[in Emma Darwin's hand]

 These lamellæ are coated with a pulpy cellular layer, with the outer cells lying free in infinite numbers. If one of these glands is punctured and squeezed, a quantity of white pulpy matter exudes, consisting of these free cells. They are minute, and vary in diameter from 2 to 6 μ. They contain in their centres a little excessively fine granular matter; but they look so like oil globules that Claparède and others at first treated them with ether. This prod

[38v]

[page in Darwin's hand]

* Archives de Zoolog. expér. July, 1874, p. 416, 419.—

† 'Zeitschrift für wissenschaft. Zoologie, B. xix. 1869, pp. 603-606.

39

[page in Emma Darwin's hand]

Ch I

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 occasionally aggregates into small rhombic crystals or into concretions, which lie between the lamellæ; but I have seen only one, and Claparède 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

40

[page in Emma Darwin's hand]

Ch I

several small, or two or three larger, or a single very large concretion of carbonate of lime, as much as 1½ mm. in diameter. When a gland includes only a few very small concretions, or, as sometimes happens, none at all, it is easily overlooked. The large concretions are round or oval, and exteriorly almost smooth. One was found which filled up not only the whole gland, as is often the case, but its neck; so that it resembled an olive-oil flask in shape. These concretions when broken are seen to be more or less crystalline in structure. How they escape from the gland is a marvel; but that they do escape is certain, for they are often found in the gizzard, intestines, and in the castings of worms, both with those kept in confinement and those in a state of nature.)

(Claparède 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 posterior glands.

41

[page in Emma Darwin's hand]

Ch I

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, lamellæ like those in the posterior glands and coated with cellular matter could be plainly seen, together with a multitude of free calciferous cells readily soluble in acetic acid. When a gland is completely filled with a single large concretion, there are no free cells, as these have been all consumed in forming the concretion. But if such a concretion, or one of only moderately large size is dissolved in acid, much membranous matter is left, which appears to consist of the remains of the formerly active lamellæ. After the formation and expulsion of a large concretion, new lamellæ 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 concretions, for near the walls

42

[page in Emma Darwin's hand]

Ch I

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 lamellæ.

Besides the free calciferous cells in which no nucleus was visible, other and rather larger free cells were seen on three occasions; and these contained a distinct nucleus and nucleolus. They were only so far acted on by acetic acid that the nucleus was thus rendered more distinct. A very small concretion was removed from between two of the lamellæ 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 I am led to suspect that the calciferous cells

43

[page in Emma Darwin's hand]

Ch I

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 irregular 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 concretions increase in size, they come into contact and unite, thus enclosing the now functionless lamellæ; 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

16 67

[page in Emma Darwin's hand]

Ch II

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

19 70

[page in Emma Darwin's hand]

Ch ii

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.)

Levens

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

20 71

[page in Emma Darwin's hand]

Ch ii

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

21 72

[page in Emma Darwin's hand]

Ch ii

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

22 73

[in Emma Darwin's hand]

Ch ii

instinctive in worms; and a very young one, born in one of my pots, dragged for some little distance a Scotchfir 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

[in Darwin's hand]

40 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

(23 74

[in Darwin's hand]

Ch. II.—

warm room, and here the result was different; for out of 42 leaves drawn into the burrows, no less than 16 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 by the air of the room being warm, and the worms consequently not being anxious to plug up their holes effectually. Pots tenanted by worms and covered with a net which allowed the entrance of cold air, were left out of doors for several nights, and now 72 leaves were all properly drawn in by their bases.

[in Emma Darwin's hand]

Petioles.—  We will now turn to the petioles or foot-stalks of compound leaves, after the leaflets have fallen off. Those from Clematis (I belive C. montana,) which grew over a verandah, were dragged early in

24 75

[page in Emma Darwin's hand]

Ch ii

January in large numbers into the burrows on an adjoining gravel-walk, lawn, and flower-bed. These petioles vary from 2½ to 4½ 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,

25 76

[page in Emma Darwin's hand]

Ch ii

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   by the worms.  It appeared therefore that the apex is generally seized in preference to the base in order that the work may be done either more conveniently or more perfectly.

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 8½ inches;

26 77

[page in Emma Darwin's hand]

Ch ii

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

27 78

[page in Emma Darwin's hand]

Ch ii

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

28 79

[page in Emma Darwin's hand]

Ch ii

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 embedded 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.(a)(Back) As all the softer parts had long ago rotted off, we may

[79v]

[page in Darwin's hand]

(a)(text)- Taking these two lots together, 56 per cent were drawn in by the base, and 44 per cent by the apex.

29 80

[in Emma Darwin's hand]

Ch ii

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 and lost.)

[in Darwin's hand]

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 & dew. The side all these triangles were three inches in length, with the base of nearly half of them one inch, & of the others half-an-inch in length. These latter triangles appeared

30 81

[page in Darwin's hand]

Ch. II

very narrow or much acuminated.* As a check on the observations presently to be given, similar triangles in a damp state were seized with fine pincers at different points & at all inclinations with reference to the margins by a very narrow pair of pincers,   & 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 distance, for instance at half-an-inch from the apex, this much was doubled back within the tube. So it was with the base & 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 & 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; & those drawn in by any point in the middle inch.)

[81V]

* In these narrow triangles the apical angle is 9° 34′ & the basal angles 85° 13′. In the broader triangles the apical angle is 19° 10′ & the basal angles 80° 25′.

[calculations]

(31 82

[page in Emma Darwin's hand]

Ch. II

Leff

(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

32 83

[page in Emma Darwin's hand]

Ch. II

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 1/20th 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 2½ 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.)

33 84

[page in Emma Darwin's hand]

Ch II

(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

34 85

[page in Emma Darwin's hand]

Ch II

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

35 86

[page in Emma Darwin's hand]

Ch II

in a 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

36 87

[page in Emma Darwin's hand]

Ch II

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

[88A]

[page in Darwin's hand]

(Small type)

Nature of Object.	Drawn into the burrows, by or near the apex.	Drawn in, by or near the middle.	Drawn in, by or near the 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 sometimes 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

[this published table differs from Darwin's draft]

(36 B.) 38 88

Ch ii

Leicester

for drawing triangles of paper into their burrows.)

(The results of the observation on the manner in which worms draw various objects into the mouths of burrows may be absorbed as follows.

 

(If we consider these several cases, we can hardly

(36 A) 37 89

[page in Emma Darwin's hand]

Ch II

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 to seize

36 C 90

[page in Emma Darwin's hand]

Ch ii

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

36 D 91

[page in Emma Darwin's hand]

Ch ii

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 à 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 or 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

36 E 92

[page in Emma Darwin's hand]

Ch ii

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* * See his interesting work, 'Souvenirs entomologiques,' 1879, p. 168 to 177.  that a Sphex—an insect belonging to the same highly-endowed order with ants—stocks its nest with

36 F 93

[page in Emma Darwin's hand]

Ch ii

paralysed grasshoppers, which are invariably dragged into the burrow by their antennæ. 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.* * Möbius, 'Die Bewegungen der Thiere,' &c., 1873, p. 111.   A cobra  

36 G 94

[page in Emma Darwin's hand]

Ch ii

was seen by Mr. Layard†  † 'Annals and Mag. of N. History,' series ii. vol. ix. 1852, p. 333.  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

36 H 95

[page in Emma Darwin's hand]

Ch ii

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;

36 I 96

[page in Emma Darwin's hand]

Ch ii

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

36 J 97

[page in Emma Darwin's hand]

Ch ii

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

36 K 98

[page in Emma Darwin's hand]

Ch ii

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.)

(37 99

[page in Darwin's hand]

Ch II.

Means by which worms excavate their burrows.—This is effected in two ways; by pushing away the earth on all sides, & by swallowing it. In the former case, the worm inserts the stretched out & attenuated anterior extremity of its body into any little crevice, or hole; & then, as Perrier remarks,* (* 'Archives de Zoolog. expér.' tom. iii. 1874, p. 405.)  the pharynx is pushed forwards into this part, which consequently swells & 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 & suction, & as a tactile organ. A worm was placed on loose mould, & it buried itself in between two & three minutes. On another occasion four worms disappeared in 15 minutes between the sides of the pot & the earth, which had been moderately pressed down. On a third occasion three large worms & a small one were placed on loose mould well mixed with fine sand & firmly pressed down, & they all disappeared, except the

(38 100

[page in Darwin's hand]

Ch. II

tail of one, in 35 minutes. On a fourth occasion six large worms were placed on argillaceous mud mixed with sand firmly pressed down, & 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, & thus rendered extremely compact. A large worm left on the surface did not succeed in penetrating it for some hours, & 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

(39 101

[page in Darwin's hand]

Ch. II

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; & their castings consisted partly of the reddish sand & partly of black earth brought up from beneath the mass. This sand had been dug up from a considerable depth, & 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; & 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 & 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, & 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. We may

40 102

[in Darwin's hand]

Ch. II

also conclude that 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.)

[in Emma Darwin's hand]

Parker

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 Claparède, evidence in its favour must be given in some detail. There is no à 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.* (* I state this on the authority of Semper, 'Reisen im Archipel der Philippinen," Th. ii. 1877, p. 30)   If earth

41 103

[in Emma Darwin's hand]

Ch ii

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

[in Darwin's hand]

the black vegetable mould 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 humus, 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

42 104

[page in Darwin's hand]

Ch ii

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.

(43 105

[page in Emma Darwin's hand]

Ch II.

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

(44 106

[in Emma Darwin's hand]

Ch II.

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 Claparède, 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.)

[in Darwin's hand]

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

[106v]

[slip glued on, some text obscured]

[in Darwin's hand]

wood cut here. The wood cut on the natural scale shows their nature curiosity [3 words illeg]

(45 107

[in Emma Darwin's hand]

Ch ii.

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 Perichæta, which have been naturalised here from the East.* (back) They rise like towers (see Fig. 2), with their summits often a little broader than their bases, sometimes to a height of above 3 and often to a height of 2½ inches. The tallest of those

(Fig. 2)

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.

[107V]

[in Darwin's hand]

Fig. 2

[woodcut proof]

(Tower-like casting from near Nice, constructed of earth, voided probably by a species of Perichæta: of natural size, copied from a photograph.—)

[107V]

[in Darwin's hand]

* 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 Perichœta 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 Perichæta 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 Perichæta abound.

(46 108

[in Emma Darwin's hand]

Ch ii

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.)   Leveuse

[in Darwin's hand]

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 humus that worms probably could not live on ordinary vegetable mould, though

47 109

[in Darwin's hand]

Ch II

he admits that they might be nourished to some extent by leaf-mould.* * 'Zeitschrift für wissenschaft. Zoolog.' B. xxviii. 1877, p. 364.  But we have seen that worms eagerly devour raw meat, fat, & dead worms; & ordinary mould can hardly fail to contain many ova, larvæ, & small living or dead creatures, spores of cryptogamic plants, & micrococci, such as those which give rise to saltpetre. These various organisms, together with some cellulose from any leaves & 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; & these traps would not have been developed unless many small animals inhabited such soil.

The depth to which worms penetrate, & the construction of their burrows. — Although worms usually live near the surface, yet they burrow to a considerable depth during long-continued dry weather & severe cold.

48 110

[in Darwin's hand]

Ch II

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 1½ 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 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.)

[in Emma Darwin's hand]

(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,

49 111

[page in Emma Darwin's hand]

Ch II

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

50 112

[page in Emma Darwin's hand]

Ch II

several burrows which passed through a layer of sifted coal-cinders, spread over turf to a thickness of 1½ 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, 3½ 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

51 113

[page in Emma Darwin's hand]

Ch II

burrows were found surrounded for lengths of 7, 4, and 3½ 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. These structures 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 linings of voided earth. Had this not been effectually done, the sharp points would have prevented the retreat of the worms into their

52 114

[page in Emma Darwin's hand]

Ch II

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 1½ 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

(53 115

[page in Darwin's hand]

Ch II

rested on the pine-leaves, was rendered probable by their clean & 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 & mould had recently been cleared away, & 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; & 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 & 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 & 41 inches,

(54 116

[in Darwin's hand]

Ch II

& these were lined or paved with little pebbles, about as large as mustard seeds; & in one of the chambers there was a decayed oat-grain, with its husk.

[in Emma Darwin's hand]

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.* * 'Zeitschrift für wissenschaft. Zoolog.' B. xxviii. 1877, p. 356.  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

(55 117

[page in Emma Darwin's hand]

Ch II

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 when not so liquid by a slow peristaltic

 

(56 118

[in Darwin's hand]

Ch II

movement. 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. As soon as a little heap is 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

[in Emma Darwin's hand]

into the burrow; and this change of direction probably serves in some manner as a protection. 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.)

(57 119

[in Emma Darwin's hand]

Ch II

(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.)

[in Darwin's hand]

It is certain that old burrows collapse in the course of time; for as we shall see in the next chapter,

(58 120

[page in Darwin's hand]

Ch II

the fine earth voided by worms, if spread out uniformly, would form in many places in the course of a year a layer 1/5; 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, & 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 & plants must likewise collapse in the course of time. The burrows of worms run down perpendicularly or a little obliquely, & 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. The deep foot-prints left at such times on our pasture-land bby the larger animals are probably in part due to the yielding of the burrows near the surface.)

(59 121

[page in Darwin's hand]

Ch II

(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, & 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 & June 13th, & rose 1·91 mm. between September 7th & 19th, much rain having fallen during the latter part of this time. During frosts & thaws the movements were twice as great.* Now when the ground swells, if it be penetrated by cylindrical holes, such as worm-burrows, their walls will tend to yield & be pressed inwards; & 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

[121V]

[page in Darwin's hand]

* These observations were made by my son Horace, who will hereafter publish an account of the movements of this stone during successive wet & dry seasons, & of the effects of its being undermined by worms. The measurements were made by id of a micrometer, & due precautions were taken with respect to changes of length in the standard from changing temperature. — [this refers to the wormstone]

60 122

[page in Darwin's hand]

Ch II

shrink a little & 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, & some of the genera have an enormous range.*  * Perrier, 'Archives de Zoolog. expér.' tom. 3, p. 378, 1874.   They inhabit the most isolated islands; they abound in Iceland, & are known to exist in the West Indies, St. Helena, Madagascar, New Caledonia & Tahiti. In the Antarctic regions, worms from Kerguelen Land have been described by Ray Lankester; & 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, & 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 work we are chiefly concerned with the earth cast up by worms, & I have gleaned a few facts on

(61 38 123

[page in Darwin's hand]

Ch II

this subject with respect to distant lands. Worms throw up plenty of castings in the United States. (a) (text back) 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, & Fritz Müller informs me "that in most parts of the forests & 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 4/5; of an inch in diameter, & 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 enquiries from gardeners & others, & from his own observations, informs me that their castings abound. He sent me some collected after heavy rain, & they consisted of little pellets, about ·15 inch in diameter; & the blackened

sandy earth of which they were formed still cohered with considerable tenacity.)

[123V]

[page in Darwin's hand]

(a) (text) (lead on)

In Venezuela, castings, probably ejected by species of Urochæta, are common in the gardens & 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, & were on an average three cubic centimeters.— (lead on)

(62 (39 124

[page in Darwin's hand]

Ch II

(The late Mr. John Scott of the Botanic Gardens near Calcutta made many observations for me on worms living under the hot & humid climate of Bengal. The castings abound almost everywhere, in jungles & in the open ground, to a greater degree, as he thinks, than in Engl&. 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; & they are probably the work of a species of Perichæta. They st& up like towers, with an open passage in the centre.

(63 125

[page in Darwin's hand]

Ch II

A figure of one of these castings from a photograph is here given (Fig. 3). The largest received by me was 3½ inches in height & 1·35 inch in diameter; another was only ¾ inch in diameter & 2¾ in height.

On the following year, Mr. Scott measured several of the largest; one was 6 inches in height & nearly 1½ in diameter: two others were 5 inches in height & respectively 2 & rather more than 2½ inches in diameter. The average weight of the 22 castings sent to me was 35 grammes (1¼ oz.); & 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.)

[125V]

[page in Darwin's hand]

Fig. 3.

[woodcut proof]

(A tower-like casting, probably ejected by a species of Perichæta, from the Botanic Garden, Calcutta: of natural size, engraved from a photograph.)

 

(64 (41 126

[page in Darwin's hand]

Ch II

(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, & are then found coiled up & apparently hybernating. Mr. Scott has never seen them at a greater depth than 2½ 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 & dry season, draw many leaves & 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

(65 (42 126bis

[page in Darwin's hand]

Ch II

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, & are reported to be from 12 to 15 inches in length, & as thick as a man's little finger. These castings were collected by Dr. King after a period of 110 days without any rain; & 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 & 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 & 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.; & the largest weighed 123·14 grammes, or 4⅓ 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, & that their diameters had thus been increased.

[126c]

to go betwn 126bis & 127

Fig. 4.

[woodcut proof]

(A casting from the Nilgiri Mountains in South India; of natural size, engraved from a photograph.)

(66 127

[page in Darwin's hand]

Ch II

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, & were surprisingly hard & 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 ·15 inch in diameter.)

(Dr. King saw in Ceylon a worm about 2 feet in length & ½ inch in diameter; & 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, & under the most different climates.)