about twice as many worms in gardens as in corn-fields.* With respect to "prairies élevées," I do not know how it may be in France, but nowhere in England have I seen the ground so thickly covered with castings as on commons, at a height of several hundred feet above the sea. In woods again, if the loose leaves in autumr. are removed, the whole surface will be found strewed with castings. Dr. King, the superintendent of the Botanic Garden in Calcutta, to whose kindness I am indebted for many observations on earthworms, informs me that he found, near Nancy in France, the bottom of the State forests covered over many acres with a spongy layer, composed of dead leaves and innumerable worm-castings. He there heard the Professor of "Aménagement des Forêts" lecturing to his pupils, and pointing out this case as a "beautiful example of the natural cultiva"tion of the soil; for year after year the "thrown-up castings cover the dead leaves; "the result being a rich humus of great "thickness."

* 'Zeitschrift für wissenschaft. Zoologie,' B. xxviii. 1877 p. 361.

*

In the year 1869, Mr. Fish rejected my conclusions with respect to the part which worms have played in the formation of vegetable mould, merely on account of their assumed incapacity to do so much work. He remarks that "considering their weakness and their

6

size, the work they are represented to "have accomplished is stupendous." Here we have an instance of that inability to sum up the effects of a continually recurrent cause, which has often retarded the progress of science, as formerly in the case of geology, and more recently in that of the principle of evolution.

Although these several objections seemed to me to have no weight, yet I resolved to make more observations of the same kind as those published, and to attack the problem on another side; namely, to weigh all the castings thrown up within a given time in a measured space, instead of ascertaining the rate at which objects left on the surface were buried by worms. But some of my observations have been rendered almost superfluous by an admirable paper by Von Hensen, * Gardeners' Chronicle,' April 17, 1869, p. 418.

already alluded to, which appeared in 1877. Before entering on details with respect to the` castings, it will be advisable to give some. account of the habits of worms from my own observations and from those of other naturalists.

CHAPTER I.

HABITS OF WORMS.

Nature of the sites inhabited-Can live long under waterNocturnal-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 tc vibrations and to touch-Feeble power of smell-TasteMental 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 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.†

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

* Bidrag till Skandinaviens Oligochætfauna,' 1871.

+ Die bis jetzt bekannten Arten aus der Familie der Regen wilmer,' 1845.