spread out and cover up any object left on the surface. I was thus led to conclude that all the vegetable mould over the whole country has passed many times through, and will again pass many times through, the intestinal canals of worms. Hence the term "animal mould" would be in some respects more appropriate than that commonly used of "vegetable mould."

Ten years after the publication of my paper, M. D'Archiac, evidently influenced by the doctrines of Elie de Beaumont, wrote about my "singulière théorie," and objected that it could apply only to "les prairies basses et humides;" and that "les terres labourées, les bois, les prairies élevées, n'apportent aucune preuve à l'appui de cette manière de voir.” * But M. D'Archiac must have thus argued from inner consciousness and not from observation, for worms abound to an extraordinary degree in kitchen gardens where the soil is continually worked, though in such loose soil they generally deposit their castings in any open cavities or within their old burrows instead of on the surface. Von Hensen estimates that there are

* Histoire des progrès de la Géologie,' tom. i. 1847, p. 224.

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 autumn 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."

་

p. 861.

Zeitschrift für wissenschaft. Zoologie,' B. xxviii. 1877

*

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

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 to 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