The formation of vegetable mould, through the action of worms : with observations on their habits /

Abstract

immediately adjoins one which has long re- mained undisturbed for pasture, and where the vegetable mould is exposed on the sides of a ditch or hole.The subject may appear an insignificant one, but we shall see that it possesses some interest ; and the maxim " de minimis lex non curat," does not apply to science.Even Elie de Beaumont, who generally undervalues small agencies and their accumulated effects, remarks.'*" la " couche tres-mince de la terre vegetale est un " monument d'une haute antiquite, et, par le " fait de sa permanence, un objet digne d'oc-" cuper le geologue, et capable de lui fournir "des remarques interessantes."Although the superficial layer of vegetable mould as a whole no doubt is of the highest antiquity, yet in regard to its permanence, we shall here- after see reason to believe that its component particles are in most cases removed at not a very slow rate, and are replaced by others due to the disintegration of the underlying materials.As I was led to keep in my study during many months worms in pots filled with earth, * ' Lcfons de Geologie Pratique,' tom.i. 1845, p. 140. HABITS OF WORMS.Chap.I. CHAPTER I. HABITS OF WORMS.Nature of the sites inhabited-Can live long under water -Nocturnal-Wander about at night-Often lie close to the mouths of their burrows, and are thus destroyed in large numbers by birds-Structure-Do not possess eyes, but can distinguish between light and darkness-Retreat rapidly when brightly illuminated, not by a reflex action-Power of attention -Sensitive to heat and cold -Completely deaf -Sensitive to vibrations and 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 glands, 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.Earth-worms 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 Scan- dinavia there are eight species, according to Chap.I. HABITS OF WORMS.Chap.I. 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 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 ; * 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 cultiva- tion of grasses in the separate form or small patches, is the impossibility of rolling or treading them firmly, withoui which no pasture can continue good."HABITS OF WORMS.Chap.I. 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 abun- dant on some grass-covered glades and in- dentations 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 feet above the sea, and at a great altitude on the Nilgiri Mountains in South India and on the Himalaya.Earth-worms must he considered as terres- trial 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 ex- posure to the dry air of a room for only a single night was fatal to them.On the Chap.I. NOCTURNAL.13 other hand he kept several large worms alive for nearty four months, completely submerged in water.*During the summer when the