Volume Ii Part 22 (1/2)
Down, October 20th, 1880.
What a man you are to do thoroughly whatever you undertake to do! The supply of specimens has been magnificent, and I have worked at them for a day and a half. I find a very few well-rounded grains of brick in the castings from over the gravel walk, and plenty over the hole in the field, and over the Roman floor. (547/2. See ”The Formation of Vegetable Mould,” 1881, pages 178 et seq. The Roman remains formed part of a villa discovered at Abinger, Surrey. Excavations were carried out, under Lord Farrer's direction, in a field adjoining the ground in which the Roman villa was first found, and extended observations were made by Lord Farrer, which led Mr. Darwin to conclude that a large part of the fine vegetable mould covering the floor of the villa had been brought up from below by worms.) You have done me the greatest possible service by making me more cautious than I should otherwise have been--viz., by sending me the rubbish from the road itself; in this rubbish I find very many particles, rounded (I suppose) by having been crushed, angles knocked off, and somewhat rolled about. But not a few of the particles may have pa.s.sed through the bodies of worms during the years since the road was laid down. I still think that the fragments are ground in the gizzards of worms, which always contain bits of stone; but I must try and get more evidence. I have to-day started a pot with worms in very fine soil, with sharp fragments of hard tiles laid on the surface, and hope to see in the course of time whether any of those become rounded. I do not think that more specimens from Abinger would aid me...
LETTER 548. TO G.J. ROMANES. Down, March 7th.
I was quite mistaken about the ”Gardeners' Chronicle;” in my index there are only the few enclosed and quite insignificant references having any relation to the minds of animals. When I returned to my work, I found that I had nearly completed my statement of facts about worms plugging up their burrows with leaves (548/1. Chapter II., of ”The Formation of Vegetable Mould through the Action of Worms,” 1881, contains a discussion on the intelligence shown by worms in the manner of plugging up their burrows with leaves (pages 78 et seq.).), etc., etc., so I waited until I had naturally to draw up a few concluding remarks. I hope that it will not bore you to read the few accompanying pages, and in the middle you will find a few sentences with a sort of definition of, or rather discussion on, intelligence. I am altogether dissatisfied with it. I tried to observe what pa.s.sed in my own mind when I did the work of a worm. If I come across a professed metaphysician, I will ask him to give me a more technical definition, with a few big words about the abstract, the concrete, the absolute, and the infinite; but seriously, I should be grateful for any suggestions, for it will hardly do to a.s.sume that every fool knows what ”intelligent” means. (548/2. ”Mr. Romanes, who has specially studied the minds of animals, believes that we can safely infer intelligence only when we see an individual profiting by its own experience...Now, if worms try to drag objects into their burrows, first in one way and then in another, until they at last succeed, they profit, at least in each particular instance, by experience” (”The Formation of Vegetable Mould,” 1881, page 95).) You will understand that the MS. is only the first rough copy, and will need much correction. Please return it, for I have no other copy--only a few memoranda. When I think how it has bothered me to know what I mean by ”intelligent,” I am sorry for you in your great work on the minds of animals.
I daresay that I shall have to alter wholly the MS.
LETTER 549. TO FRANCIS GALTON. Down, March 8th [1881].
Very many thanks for your note. I have been observing the [worm] tracks on my walks for several months, and they occur (or can be seen) only after heavy rain. As I know that worms which are going to die (generally from the parasitic larva of a fly) always come out of their burrows, I have looked out during these months, and have usually found in the morning only from one to three or four along the whole length of my walks. On the other hand, I remember having in former years seen scores or hundreds of dead worms after heavy rain. (549/1. ”After heavy rain succeeding dry weather, an astonis.h.i.+ng number of dead worms may sometimes be seen lying on the ground. Mr. Galton informs me that on one occasion (March, 1881), the dead worms averaged one for every two-and-a-half paces in length on a walk in Hyde Park, four paces in width” (loc. cit., page 14).) I cannot possibly believe that worms are drowned in the course of even three or four days' immersion; and I am inclined to conclude that the death of sickly (probably with parasites) worms is thus hastened. I will add a few words to what I have said about these tracks. Occasionally worms suffer from epidemics (of what nature I know not) and die by the million on the surface of the ground. Your ruby paper answers capitally, but I suspect that it is only for dimming the light, and I know not how to illuminate worms by the same intensity of light, and yet of a colour which permits the actinic rays to pa.s.s. I have tried drawing triangles of damp paper through a small cylindrical hole, as you suggested, and I can discover no source of error. (549/2.
Triangles of paper were used in experiments to test the intelligence of worms (loc. cit., page 83).) Nevertheless, I am becoming more doubtful about the intelligence of worms. The worst job is that they will do their work in a slovenly manner when kept in pots (549/3. Loc. cit., page 75.), and I am beyond measure perplexed to judge how far such observations are trustworthy.
LETTER 550. TO E. RAY LANKESTER.
(550/1. Mr. Lankester had written October 11th, 1881, to thank Mr.
Darwin for the present of the Earthworm book. He asks whether Darwin knows of ”any experiments on the influence of sea-water on earthworms.
I have a.s.sumed that it is fatal to them. But there is a littoral species (Pontodrilus of Perrier) found at Ma.r.s.eilles.” Lankester adds, ”It is a great pleasure and source of pride to me to see my drawing of the earthworm's alimentary ca.n.a.l figuring in your pages.”
Down, October 13th [1881].
I have been much pleased and interested by your note. I never actually tried sea-water, but I was very fond of angling when a boy, and as I could not bear to see the worms wriggling on the hook, I dipped them always first in salt water, and this killed them very quickly. I remember, though not very distinctly, seeing several earthworms dead on the beach close to where a little brook entered, and I a.s.sumed that they had been brought down by the brook, killed by the sea-water, and cast on sh.o.r.e. With your skill and great knowledge, I have no doubt that you will make out much new about the anatomy of worms, whenever you take up the subject again.
LETTER 551. TO J.H. GILBERT. Down, January, 12th, 1882.
I have been much interested by your letter, for which I thank you heartily. There was not the least cause for you to apologise for not having written sooner, for I attributed it to the right cause, i.e. your hands being full of work.
Your statement about the quant.i.ty of nitrogen in the collected castings is most curious, and much exceeds what I should have expected. In lately reading one of your and Mr. Lawes' great papers in the ”Philosophical Transactions” (551/1. The first Report on ”Agricultural, Botanical, and Chemical Results of Experiments on the Mixed Herbage of Permanent Gra.s.sland, conducted for many years in succession on the same land,” was published in the ”Philosophical Transactions of the Royal Society” in 1880, the second paper appeared in the ”Phil. Trans.” for 1882, and the third in the ”Phil. Trans.” of 1900, Volume 192, page 139.) (the value and importance of which cannot, in my opinion, be exaggerated) I was struck with the similarity of your soil with that near here; and anything observed here would apply to your land. Unfortunately I have never made deep sections in this neighbourhood, so as to see how deep the worms burrow, except in one spot, and here there had been left on the surface of the chalk a little very fine ferruginous sand, probably of Tertiary age; into this the worms had burrowed to a depth of 55 and 61 inches. I have never seen here red castings on the surface, but it seems possible (from what I have observed with reddish sand) that much of the red colour of the underlying clay would be discharged in pa.s.sing through the intestinal ca.n.a.l.
Worms usually work near the surface, but I have noticed that at certain seasons pale-coloured earth is brought up from beneath the outlying blackish mould on my lawn; but from what depth I cannot say. That some must be brought up from a depth of four or five or six feet is certain, as the worms retire to this depth during very dry and very cold weather.
As worms devour greedily raw flesh and dead worms, they could devour dead larvae, eggs, etc., etc., in the soil, and thus they might locally add to the amount of nitrogen in the soil, though not of course if the whole country is considered. I saw in your paper something about the difference in the amount of nitrogen at different depths in the superficial mould, and here worms may have played a part. I wish that the problem had been before me when observing, as possibly I might have thrown some little light on it, which would have pleased me greatly.
2.IX.VIII. MISCELLANEOUS, 1846-1878.
(552/1. The following four letters refer to questions connected with the origin of coal.)
LETTER 552. TO J.D. HOOKER. Down, May [1846].
I am delighted that you are in the field, geologising or palaeontologising. I beg you to read the two Rogers' account of the Coal-fields of N. America; in my opinion they are eminently instructive and suggestive. (552/1. ”On the Physical Structure of the Appalachian Chain,” by W.B. and H.D. Rogers. Boston, 1843. See also ”Geology of Pennsylvania,” by H.D. Rogers. 4 volumes. London and Philadelphia, 1843.) I can lend you their resume of their own labours, and, indeed, I do not know that their work is yet published in full. L. Horner gives a capital balance of difficulties on the Coal-theory in his last Anniversary Address, which, if you have not read, will, I think, interest you. (552/2. ”Quart. Journ. Geol. Soc.” Volume II., 1846, page 170.) In a paper just read an author (552/3. ”On the Remarkable Fossil Trees lately discovered near St. Helen's.” By E.W. Binney. ”Phil.
Mag.” Volume XXIV., page 165, 1844. On page 173 the author writes: ”The Stigmaria or Sigillaria, whichever name is to be retained... was a tree that undoubtedly grew in water.”) throws out the idea that the Sigillaria was an aquatic plant (552/4. See ”Life and Letters,” I., pages 356 et seq.)--I suppose a Cycad-Conifer with the habits of the mangrove. From simple geological reasoning I have for some time been led to suspect that the great (and great and difficult it is) problem of the Coal would be solved on the theory of the upright plants having been aquatic. But even on such, I presume improbable notion, there are, as it strikes me, immense difficulties, and none greater than the width of the coal-fields. On what kind of coast or land could the plants have lived?
It is a grand problem, and I trust you will grapple with it. I shall like much to have some discussion with you. When will you come here again? I am very sorry to infer from your letter that your sister has been ill.
LETTER 553. TO J.D. HOOKER. [June 2nd, 1847.]