Search Results - The Complete Work of Charles Darwin Online

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

inches beneath the surface, these must have been buried by the worms whilst the land was in pasture before it was ploughed, for other-wise they would have been indiscriminately scattered by the plough throughout the whole thickness of the soil. Four-and-a-half years afterwards I had three holes dug in this field, in which potatoes had been lately planted, and the layer of marl-fragments was now found 13 inches beneath the bottoms of the furrows, and therefore probably 15 inches 1809, that is twenty

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

CHAP. III. BROUGHT UP BY WORMS. ated in soil containing vegetable matter, as well as to the humus-acids.* The projecting corners would also, relatively to the other parts, have been embraced by a larger number of living rootlets; and these have the power of even attacking marble, as Sachs has shown. Thus, in the course of 29 years, buried angular fragments of chalk had been converted into well-rounded nodules. Another part of this same field was mossy, and as it was thought that sifted coal

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

AMOUNT OF EARTH CHAP. III. lying layer of turf, the small flag-stones, all in their proper places, were found covered by an inch of fine mould. Two recently published accounts of sub-stances strewed on the surface of pasture-land, having become buried through the action of worms, may be here noticed. The Rev. H. C. Key had a ditch cut in a field, over which coal-ashes had been spread, as it was believed, eighteen years before; and on the clean-cut perpendicular sides of the ditch, at a depth

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

GREAT STONES CHAP. III. it is, that boulders which at some ancient period have rolled down from a rocky mountain or cliff on to a meadow at its base, are always somewhat imbedded in the soil; and, when removed, leave an exact impression of their lower surfaces in the underlying fine mould. If, however, a boulder is of such huge dimensions, that the earth beneath is kept dry, such earth will not be inhabited by worms, and the boulder will not sink into the ground. A lime-kiln formerly stood in

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

CHAP. III. UNDERMINED BY WORMS. had never since been moved; nor could this easily have been done, as, when I had them removed, it was the work of two men with levers. One of these stones, and not the largest, was 64 inches long, 17 inches broad, and from 9 to 10 inches in thickness. Its lower surface was somewhat protuberant in the middle; and this part still rested on broken bricks and mortar, showing the truth of the old workman's account. Beneath the brick rubbish the natural sandy soil

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

turf-covered sloping border round the stone, on which many castings had recently been ejected, was 10 inches in thickness; and most of this mould must have been brought up by worms from beneath its base. At a distance of 8 yards from the stone, the mould was only 5 1/2 inches in thickness (with a piece of tobacco pipe at a depth of 4 inches), and this rested on broken flint and chalk which could not have easily yielded to the pressure or weight of the stone. A straight rod was fixed horizontally

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

imbedded objects, and their parallelism with the surface of the land, are the most striking features of the case; for this parallelism shows how equably the worms must have worked; the result being, however, partly the effect of the washing down of the fresh castings by rain. The specific gravity of the objects does not affect their rate of sinking, as could be seen by porous cinders, burnt marl, chalk and quartz pebbles, having all sunk to the same depth within the same time. Considering the nature of

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

WEIGHT OF EARTH CHAP. III. square foot, in a place abounding with worms, on the summit of a bank, where no castings could have rolled down from above. These castings must have been ejected, as he judged from their appearance in reference to the rainy and dry periods near Nice, within the previous five or six months; they weighed 9 1/2 oz., or 5 lb. 5 1/2 oz. per square yard. After an interval of four months, Dr. King collected all the castings subsequently ejected on the same square foot of

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

WEIGHT OF EARTH CHAP. III. during a year all the castings thrown up on two separate square yards, near Leith Hill Place, in Surrey. The amount collected was, however, somewhat less than that originally ejected by the worms; for, as I have repeatedly observed, a good deal of the finest earth is washed away, whenever castings are thrown up during or shortly before heavy rain. Small portions also adhered to the surrounding blades of grass, and it required too much time to detach every one of them

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

CHAP. IV. OF ANCIENT BUILDINGS. Roman emperors, dating from 133 to 361, and perhaps to 375 A.D., were likewise found. Also a half-penny of George I., 1715. The presence of this latter coin seems an anomaly; but no doubt it was dropped on the ground during the last century, and since then there has been ample time for its burial under a considerable depth of the castings of worms. From the different dates of the Roman coins we may infer that the building was long inhabited. It was probably

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

signs of having been penetrated by worms; and although the overlying fine mould closely resembled that which in many [page]18

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

own observation, is an analogous case. Even those parts of the concrete floor which the worms could not penetrate would almost certainly have been undermined, and would have sunk, like the great [page] 19

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

cleared out the holes about a month before, but a good many castings had since been ejected. I suspect that he imagined that he swept the pavements oftener than he really did, for the conditions were in several respects very unfavourable for the accumulation of even a moderate amount of castings. The tiles are rather large, viz., about 5 1/2 inches square, and the mortar between them was in most places sound, so that the worms were able to bring up earth from below only at certain points. The tiles

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

buried beneath mould and turf. It is not probable that they can have been undermined by worms, for their foundations would no doubt have been laid at a considerable depth. If they have not subsided, the stones of which the columns were constructed must have been removed from beneath the former level of the floor. Chedworth, Gloucestershire. —The remains of a large Roman villa were discovered here in 1866, on ground which had been covered with wood from time immemorial. No suspicion seems ever to

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

BURIAL OF THE REMAINS CHAP. IV. encountered some remains.* But subsequently the tops of some stone walls were detected in parts of the wood, projecting a little above the surface of the ground. Most of the coins found here belonged to Constans (who died 350 a.d.) and the Constantine family. My sons Francis and Horace visited the place in November 1877, for the sake of ascertaining what part worms may have played in the burial of these extensive remains. But the circumstances were not

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

walls during this long period. It appears to have been destroyed by fire, and most of the stones used in the buildings have since been carried away. These circumstances are unfavourable for ascertaining the part which worms have played in the burial of the ruins; but as careful sections of the rubbish overlying an ancient town have seldom or never before been made in England, I will give copies of the most characteristic portions of some of those made by Mr. Joyce. They are of too great length to

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

mortar or concrete, which has since decayed, some of the lime probably having been dissolved. The disturbed state of the rubbish may have been due to its having been searched for building stones. This bed was capped by fine vegetable mould, 9 inches in thickness. From these facts we may conclude that the Hall was burnt down, and that much rubbish fell on the floor, through and from which the worms slowly brought up the mould, now forming the surface of the level field. A section across the middle

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

points which more immediately concern us. Worm-castings were observed on the floors of several of the rooms, in one of which the tesselation was unusually perfect. The tesseræ here consisted of little cubes of hard sandstone of about 1 inch, several of which were loose or projected slightly above the general level. One or occasionally two open worm-burrows were found beneath all the loose tesseræ. Worms have also penetrated the old walls of these ruins. A wall, which had just been exposed to view

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

should have been careless about the solidity of the bed on which their tesselated and often ornamented pavements were laid. The sinking must, as it appears to me, be attributed in chief part to the pavement having been undermined by worms, which we know are still at work. Even Mr. Joyce at last admitted that this could not have failed to have produced a considerable effect. Thus also the large quantity of fine mould overlying the pavements can be accounted for, the presence of which would

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

the ground in the above section is rendered intelligible. For worms will continually have brought up fine earth from below, which will have been stirred [page] 22

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

CHAP. IV. OF ANCIENT BUILDINGS. up by the plough whenever the land was cultivated. But after a time a greater thickness of fine earth will thus have been accumulated than could be reached by the plough; and a bed like the 25 1/2-inch mass, in Fig. 14, will have been formed beneath the superficial mould, which latter will have been brought to the surface within more recent times, and have been well sifted by the worms. Wroxeter, Shropshire. —The old Roman city of Uriconium was founded in the

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

was first cultivated the old walls were perhaps intentionally pulled down, and that hollow places were filled up. This may have been the case; but if after the desertion of the city the land was left for many centuries uncultivated, worms would have brought up enough fine earth to have covered the ruins completely; that is if they had subsided from having been under-mined. The foundations of some of the walls, for instance those of the portion still standing about 20 feet above the ground, and

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

CHAP. IV. OF ANCIENT BUILDINGS. ally so deep. The mortar employed in the buildings must have been excellent, for it is still in parts extremely hard. Wherever walls of any height have been exposed to view, they are, as Dr. Johnson believes, still perpendicular. The walls with such deep foundations cannot have been under-mined by worms, and therefore cannot have subsided, as appears to have occurred at Abinger and Silchester. Hence it is very difficult to account for their being now completely

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

DISINTEGRATION CHAP. V. countries, worms aid in the work of denudation in several ways. The vegetable mould which covers, as with a mantle, the surface of the land, has all passed many times through their bodies. Mould differs in appearance from the subsoil only in its dark colour, and in the absence of fragments or particles of stone (when such are present in the subsoil), larger than those which can pass through the alimentary canal of a worm. This sifting of the soil is aided, as has

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

DISINTEGRATION CHAP. V. carbonate of lime and on the oxides of iron. It is also known that some of these acids, which were called long ago by Thénard azo-humic, are enabled to dissolve colloid silica in proportion to the nitrogen which they contain.* In the formation of these latter acids worms probably afford some aid, for Dr. H. Johnson informs me that by Nessler's test he found 0.018 per cent, of ammonia in their castings. It may be here added that I have recently been informed by Dr

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

appear, as we have just seen, to be generated within the bodies of worms during the digestive process, and their acid salts, play a highly important part, according to the recent observations of Mr. Julien, in the disintegration of various kinds of rocks. It has long been known that the carbonic acid, and no doubt nitric and nitrous acids, which are present in rain-water, act in like manner. There is, also, a great excess of carbonic acid in all soils, especially in rich soils, and this is

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

CHAP. V. AND DENUDATION. continually exposed to chemical decomposition; and thus the amount of soil will tend to increase. As worms line their burrows with their castings, and as the burrows penetrate to a depth of 5 or 6, or even more feet, some small amount of the humus-acids will be carried far down, and will there act on the underlying rocks and fragments of rock. Thus the thickness of the soil, if none be removed from the surface, will steadily though slowly tend to increase; but the

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

CHAP. V. AND DENUDATION. and very many of these beads and fragments were picked up and swallowed by the worms, for they were found in their castings, intestines, and gizzards. They even swallowed the coarse red dust, formed by the pounding of the tiles. Nor can it be supposed that they mistook the beads and fragments for food; for we have seen that their taste is delicate enough to distinguish between different kinds of leaves. It is therefore manifest that they swallow hard objects, such as

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

many of those extracted from the gizzards of worms, but the larger ones were somewhat smoother. Four castings found on the recently uncovered, tesselated floor of the great room in the Roman villa at Brading, contained many particles of tile or brick, of mortar, and of hard white cement; and the majority of these appeared plainly worn. The particles of mortar, however, seemed to have suffered more corrosion than attrition, for grains of silex often projected from their surfaces. Castings from

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

DISINTEGRATION CHAP. V. in the gizzards of worms is of more importance under a geological point of view than may at first appear to be the case; for Mr. Sorby has clearly shown that the ordinary means of disintegration, namely, running water and the waves of the sea, act with less and less power on fragments of rock the smaller they are. Hence, as he remarks, even making no allowance for the extra buoying up of very minute particles by a current of water, depending on surface cohesion, the

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

accumulation of disintegrated castings—Castings blown to leeward over level land—An attempt to estimate the amount thus blown—The degradation of ancient encampments and tumuli—The preservation of the crowns and furrows on land anciently ploughed—The formation and amount of mould over the Chalk formation. We are now prepared to consider the more direct part which worms take in the denudation of the land. When reflecting on subaerial denudation, it formerly appeared to me, as it has to others, that a

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

CHAP. VI. AIDED BY WORMS. me after heavy rain, in many places on land of all kinds. On the flowing of wet castings, and the rolling of dry disintegrated eastings down inclined surfaces, —When castings are ejected on an inclined surface during or shortly before heavy rain, they cannot fail to flow a little down the slope. Thus, on some steep slopes in Knole Park, which were covered with coarse grass and had apparently existed in this state from time immemorial, I found (Oct. 22, 1872) after

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

CHAP. VI. AIDED BY WORMS. still be detected. On another occasion, after rain which was never heavy, but which lasted for 18 hours, all the castings on this same gently inclined lawn had lost their vermiform structure; and they had flowed, so that fully two-thirds of the ejected earth lay below the mouths of the burrows. These observations led me to make others with more care. Eight castings were found on my lawn, where the grass-blades are fine and close together, and three others on a field

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

CHAP. VI. AIDED BY WORMS. castings on the same lawn where the mean slope was 12° 5'. We may, however, take the above eleven cases, which are accurate as far as they go, and calculate the weight of the ejected earth which annually flows down a slope having a mean inclination of 9° 26'. This was done by my son George. It has been shown that almost exactly two-thirds of the ejected earth is found below the mouth of the burrow and one-third above it. Now if the two-thirds which is below the hole

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

DENUDATION OF THE LAND CHAP. VI. average length of ten out of the above eleven eastings was 2.03 inches, and half of this we may take as being one inch. It may therefore be concluded that one-third of the whole earth brought to the surface was in these cases carried down the slope through one inch. It was shown in the third chapter that on Leith Hill Common, dry earth weighing at least 7.453 lbs. was brought up by worms to the surface on a square yard in the course of a year. If a square yard

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

CHAP. VI. AIDED BY WORMS. annually cross a horizontal line, 100 yards in length, on a hill-side having this inclination. A more accurate, though still very rough, calculation can be made of the bulk of earth, which in its natural damp state annually flows down the same slope over a yard-line drawn horizontally across it. From the several cases given in the third chapter, it is known that the castings annually brought to the surface on a square yard, if uniformly spread out would form a layer

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

CHAP. VI. AIDED BY WORMS. its castings, not in vermiform masses, but in little pellets of varying sizes: these are very numerous in some places, and Mr. Scott says that they are washed away by every shower. I was led to believe that a considerable quantity of fine earth is washed quite away from castings during rain, from the surfaces of old ones being often studded with coarse particles. Accordingly a little fine precipitated chalk, moistened with saliva or gumwater, so as to be slightly

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

CHAP. VI. AIDED BY WORMS. these eastings are extremely liable to crumble during dry weather into small fragments, which are soon acted on by rain, and then sink down so as to be no longer distinguishable from the surrounding soil. He sent me a mass of such disintegrated castings, collected on the top of a bank, where none could have rolled down from above. They must have been ejected within the previous five or six months, but they now consisted of more or less rounded fragments of all sizes

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

CHAP. VI. LEDGES ON HILL-SIDES. bleached petioles, in comparison with those of other plants of the same kind, where there had been no such accumulation. The earth thus accumulated had no doubt been secured (as I have everywhere seen) by the smaller roots of the plants. After describing this and other analogous cases, Dr. King concludes: I can have no doubt that worms help greatly in the process of denudation. Ledges of earth on steep hillsides. —Little horizontal ledges, one above another

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

obliterated by rain and other atmospheric agencies. There is some analogy between the formation, as here supposed, of these ledges, and that of the ripples of wind-drifted sand as described by Lyell.* The steep, grass-covered sides of a mountainous valley in Westmoreland, called Grisedale, was marked in many places with innumerable lines of miniature cliffs, with almost horizontal, little ledges at their bases. Their formation was in no way connected with the action of worms, for castings could

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

CHAP. VI. ANCIENTLY PLOUGHED FIELDS two inches in 10 years. Therefore in so long a period as 2000 years, a large amount of earth will have been repeatedly brought to the surface on most old embankments and tumuli, especially on the talus round their bases, and much of this earth will have been washed completely away. We may therefore conclude that all ancient mounds, when not formed of materials unfavourable to worms, will have been somewhat lowered in the course of centuries, although their

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

DENUDATION OF THE LAND. CHAP. VI. whole it appears that the crowns and furrows on land formerly ploughed, but now covered with grass, tend slowly to disappear when the surface is inclined; and this is probably in large part due to the action of worms; but that the crowns and furrows last for a very long time when the surface is nearly level. Formation and amount of mould over the Chalk Formation.—Worm-castings are often ejected in extraordinary numbers on steep, grass-covered slopes, where the

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

, averaged rather less than 3 1/2 inches in thickness. Why worms should penetrate and bring up chalk in some places and not in others I do not know. In many districts where the land is nearly level, a bed several feet in thickness of red clay full of unworn flints overlies the Upper Chalk. This overlying matter, the surface of which has been converted into mould, consists of the undissolved residue from the chalk. It may be well here to recall the case of the fragments of chalk buried beneath worm

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

of time; for although I do not know how thin a layer of mould suffices to support worms, yet a limit must at last be reached; and then their cast [page] 30

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

by measurements and calculations that on a surface with a mean inclination of 9° 26', 2.4 cubic inches of earth which had been ejected by worms crossed, in the course [page] 31

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

CONCLUSION. CHAP. VII. 18 inches in diameter, which was filled with sand, on which fallen leaves were strewed; and these were soon dragged into their burrows to a depth of 3 inches. After about 6 weeks an almost uniform layer of sand, a centimeter (.4 inch) in thickness, was converted into humus by having passed through the alimentary canals of these two worms. It is believed by some persons that worm burrows, which often penetrate the ground almost perpendicularly to a depth of 5 or 6 feet

16%

F1362 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. 6th thousand (corrected). London: John Murray. Text Image PDF

CHAP. VII. CONCLUSION. 315 Worms are poorly provided with sense organs, for they cannot be said to see, although they can just distinguish between light and darkness; they are completely deaf, and have only a feeble power of smell; the sense of touch alone is well developed. They can therefore learn but little about the outside world, and it is surprising that they should exhibit some skill in lining-their burrows with their castings and with leaves, and in the case of some species in piling

16%

F1364 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. Seventh thousand. Corrected by Francis Darwin. London: John Murray. Text Image PDF

during many months worms in pots filled with earth, * ' Lecons de G ologie Pratique,' tom, i. 1845, p. 140. [page]

16%

F1364 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. Seventh thousand. Corrected by Francis Darwin. London: John Murray. Text Image PDF

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 extraordinary rapidity into their 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

16%

F1364 Book: Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. Seventh thousand. Corrected by Francis Darwin. London: John Murray. Text Image PDF

different occasions might be explained, either by the degree of extension of their skin and its consequent transparency, or by some particular incidence of the light; but I could discover no such relation. One thing was manifest, namely, that when worms were employed in dragging leaves into their burrows or in eating them, and even during the short intervals whilst they rested from their work they either did not perceive the light or were regardless of it; and this occurred even when the light