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THE habits of worms and the purpose they fulfil in the economy of Nature do not at first sight appear to be very promising subjects of inquiry, nor likely to lead to interesting results; yet the work which has just been published by Mr. DARWIN, "On the Formation of Vegetable Mould through the Action of Worms,"1 shows how the facts accumulated by a careful and accomplished observer may render an uninviting subject extremely interesting, and serve as a basis on which theories having an important relation to geology may rest. It is remarkable that, notwithstanding their common occurrence, no monograph of the British species has been written. It is probable, however, that there are about eight species. All of them are probably terrestrial, though they resemble other annelids in being able to live for a considerable period under water. Salt or brackish water proves rapidly fatal to them, as was demonstrated not long ago on the occasion of a high tide overflowing the banks of the Medway at Rochester, when many thousands of worms might be seen lying dead on the surface.

Worms are nocturnal in their habits, and only exceptionally leave their burrows by day; those that are found wandering on the surface are, Mr. DARWIN thinks, sick individuals affected by the parasitic larvæ of a fly. They do not, however, bury themselves deeply except in very hot or very cold weather, but lie with their heads near the surface, partly perhaps for warmth, but more probably for respiratory purposes. The senses of worms, with the exception of that of touch, appear to be very feebly developed. Their sensitiveness to light varies remarkably, the sudden admission and shutting off of a bright light concentrated on the head sometimes producing no effect, whilst at others it induces a rapid retreat of the animal into its burrow. Both Mr. DARWIN and HOFMEISTER agree in thinking that light affects worms by its duration as well as its intensity, the light of a candle even causing them to withdraw or preventing them from issuing from their holes at night. They do not appear to possess any sense of hearing, remaining quiet both when a shrill metal whistle and a bassoon were sounded near them. Their faculty of smell, again, seems to be only developed so far as to enable them to distinguish the proximity of the favourite objects of food, for they remained unexcited by many odours, though they soon discovered and carried off fragments of onion and cabbage. Their sensitiveness to contact, on the other hand, is very acute, and the slightest vibration, or even the impression produced by a feeble puff of air, is sufficient to induce rapid movement. They are omnivorous; they like particles of meat and fat, and do not refuse the dead body of another worm. Their digestive fluids are found to resemble the pancreatic juice, and to digest albumen, fats, and starch. Everyone must have been struck with the leaves and petioles of leaves, that are so frequently found standing nearly vertically in the soil. These are probably often thought to be merely accidentally imbedded, but it is well known that they are objects seized by worms and dragged into their burrows, partly for food and partly to close the orifice; the latter object being demonstrated by the fact that small stones are gathered together and similarly placed. Mr. DARWIN'S observations on this point are very interesting. He describes the mode in which they seize such objects, showing that it is partly by the lips and partly by suction, and that they evince a certain amount of intelligence in the mode in which they, if the expression may be allowed, manipulate them, so that they are always dragged to their holes with the least expenditure of force. The mode in which worms form their burrows has engaged Mr. DARWIN'S attention, and he thinks it is partly effected by a wedge-like cleaving process, and partly by swallowing the earth immediately in front of them. They penetrate sometimes to a depth of five or six feet, and there form chambers, where many hibernate, rolled together in a ball. He does not think HENSEN's estimate of 53,767 worms to an acre too high an estimate, and this

1 London: John Murray, Albemarle-street.

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number would weigh 356 lb., whilst their castings reached the surprising amount in one instance of 7'56 tons per acre, and in another of 16'1 tons per acre-an amount that, considering all this had passed through the bodies of the worms, is sufficient to show how important a part these animals play in the economy of Nature.