Darwin on humus and the earthworms : the formation of vegetable mould through the action of worms with observations on their habits / by Charles Darwin ; with an introduction by Sir Albert Howard.

  • Darwin, Charles, 1809-1882.
Date:
1945
Catalogue details

Licence: Public Domain Mark

Credit: Darwin on humus and the earthworms : the formation of vegetable mould through the action of worms with observations on their habits / by Charles Darwin ; with an introduction by Sir Albert Howard. Source: Wellcome Collection.

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    and 16 by the apex. Taking these two lots together, 56 per cent were drawn in by the base, and 44 per cent by the apex. As all the softer parts had long ago rotted off, we may feel sure, especially in the latter case, that none had been drawn in as food. At this season, therefore, worms drag these petioles into their burrows indifferently by either end, a slight preference being given to the base. This latter fact may be accounted for by the difficulty of plugging up a burrow with objects so extremely thin as are the upper ends. In support of this view, it may be stated that out of the 16 petioles which had been drawn in by their upper ends, the more attenuated terminal portion of 7 had been previously broken off by some accident. Triangles of paper. Elongated triangles were cut out of moderately stiff writing paper, which was rubbed with raw fat on both sides, so as to prevent their becoming excessively limp when exposed at night to rain and dew. The sides of all the triangles were three inches in length, with the bases of 120 one inch, and of the other 183 half an inch in length. These latter triangles were very narrow or much acuminated.1 As a check on the observations presently to be given, similar triangles in a damp state were seized by a very narrow pair of pincers at different points and at all inclinations with reference to the margins, and were then drawn into a short tube of the diameter of a worm-burrow. If seized by the apex, the triangle was drawn straight into the tube, with its margins infolded; if seized at some little distance from the apex, for instance at half an inch, this much was doubled back within the tube. So it was with the base and basal angles, though in this case the triangles offered, as might have been expected, much more resistance to being drawn in. If seized near the middle the triangle was doubled up, with the apex and base left sticking out of the tube. As the sides of the tri¬ angles were three inches in length, the result of their being drawn into a tube or into a burrow in different ways, may be conveniently divided into three groups: those drawn in by the apex or within an inch of it; those drawn in by the base or within an inch of it; and those drawn in by any point in the middle inch. In order to see how the triangles would be seized by worms, some in a damp state were given to worms kept in confinement. They were seized in three different manners in the case of both the narrow and broad triangles: viz. by the margin; by one of the three angles, which was often completely engulfed in their mouths; and lastly, by suction applied to any part of the flat surface. If lines parallel to the base and 1 In these narrow triangles the apical angle is 9° 34', and the basal angles 85° 13'. In the broader triangles the apical angle is 19° 10' and the basal angles 80° 25'.