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THE common earth-worm comes within the cognizance of the ordinary observer chiefly as a useful bait to be impaled on a hook and thus used for attracting fish for the sport of the angler. The juvenile representatives of the brotherhood of the rod have generally learned to recognize the whereabouts of their victim by con glomerations of little pellets of earth here and there; and know- ing ones are wont to cautiously explore localities so indicated with lantern at night or in the early morning, and there find the worms partly or entirely outside their holes. Few of the many who have learned thus much of the animal in question have ever thought of the important functions in the economy of nature performed by the humble being. Even as far back as 1837, however, Mr. Darwin had appreciated the role that it plays and communicated to the Geological Society of London a special memoir "On the Formation of Mould" by worms. Considerable scepticism was evoked respecting his conclusions, so insignificant did the means appear to the end, but the author has now supplemented his numerous works by a special monograph on the subject, and has fortified and amplified his early studies and conclusions. As Darwin says, some observant 'farmers are aware that objects of all kinds left on the surface of pasture land after a time disappear, or, as they say, work themselves downward.' This disappearance is of course due to no automatic process of the objects sinking down, but really to the cumulative effect of worms' castings. The doubt such a statement may excite will be dissipated by a knowledge of what a worm can do in a given period, and the multiplication of that amount by number and time. Hensen, in experiments made on worms in confinement and fed on leaves, found that they ejected about eight grains of earth a day; but, according to Darwin, 'a very much larger amount must be ejected by worms in their natural state, at the periods when they consume earth as food instead of leaves; and when they are making deep burrows.' In corroboration of this opinion, Darwin has tabulated the results of numerous observations on the weight of the castings accumulated at the mouth of a single burrow. Before weighing the castings were dried (excepting in one specified instance) by exposure during many days' to the sun or before a hot fire. These castings for each hole generally exceeded an ounce in weight after being. dried, and sometimes nearly equalled a quarter of a go On the Nilgiri mountains one casting even exceeded this latter weight. The largest castings in England were found on extremely poor pasture land; and these are generally larger than those on land producing a rich vegetation. It would appear that worms have to swallow a greater amount of earth on poor than on rich land: in order to obtain sufficient nutriment.' (P. 162.) In another place we are told that Hensen: found that 'there must exist 133,000 liv- ing worms in a hectare of land, or 53,767 in an acre. This latter number of worms would weigh: 356 pounds, taking Hensen's standard of the weight of a single worm, namely, one gram. It should, however, be noted, says Mr. Darwin, 'that this calculation is founded on the numbers found' in a garden, and Hensen believes that worms are twice as numerous in gardens-as in cornfields.' On the other hand recent observations demonstrate that worms may occur in even much greater numbers than were found by Hensen.

A little calculation will convince the most sceptical that worms with the habits thus indicated and in the numbers known to occur must in time produce great effects. Mr. Darwin has been observing their habits and doings for many years. 'Near Maer Hall in Staffordshire, quick-lime had been spread, about the year 1827, thickly over a field of good pasture-land which had not since been ploughed. Some square holes were dug in this field in the beginning of October 1837; and the sections showed a layer of turf-formed by the matted roots of the grasses, 1/2 inch in thickness, beneath which, at a depth of 2 1/2 inches (or 3 inches from the surface), a layer of the lime in powder or in small lumps could be distinctly seen running all round the vertical sides of the Holes.' (P. 130.) Again, a quantity of broken chalk was spread on December 20th, 1842, over a part of a field near Darwin's house. 'The chalk was laid on the land for the sake of observing at some future period to what depth it would become buried. At the end of November 1871—that is, after an interval of 29 years—a trench was dug across this part of the field; and a line of white nodules could be traced at a depth of 7 inches from the surface. The mould, therefore (exclusive of the turf), had been thrown up at an average rate of .22 inch per year.' (P. 139.) In view of such operations we can readily account for the burial of ancient cities and towns, and a number of cases in point are cited in a special chapter on 'the part which worms have played in the burial of ancient buildings.' The subsidence of pavements, the burial of Roman villas at Abinger, Chedworth, Brading, and elsewhere, the entombment of the Roman towns of Silchester, Wroxeter, etc., are shown to' be mainly due to the action of worms. We can readily comprehend, therefore, how it is that the more ancient cities which once flourished in Asia and the older seats of civilization have been' covered to such a depth as to have been entirely concealed, even without taking into consideration the accumulation of dust.

But we have already lingered too long over Mr. Darwin's interesting and suggestive treatise. For information on the habits of worms and the other effects which they produce in the configuration of the surface of the earth, as well as for much other incidental information, we must refer to the volume itself. That it is well written and well worth reading Darwin's name implies.

* The Formation of Vegetable Mould through the Action of Earth-Worms, with Observations on their Habits. By Charles Darwin. With illustrations. $1.50. New York: D. Appleton & Co.