It may be suggested with much apparent probability that so large a proportion of the triangles were drawn in by the apex, not from the worms having selected this end as the most convenient for the purpose, but from having first tried in other ways and failed.This notion was countenanced by the manner in which worms in confinement were seen to drag about and drop the triangles; but then they were working carelessly.I did not at first perceive the importance of this subject, but merely noticed that the bases of those triangles which had been drawn in by the apex, were generally clean and not crumpled.The subject was afterwards attended to carefully.In the first place several triangles which had been drawn in by the basal angles, or by the base, or a little above the base, and which werethus much crumpled and dirtied, were left for some hours in water and were then well shaken while immersed; but neither the dirt nor the creases were thus removed.Only slight creases could be obliterated, even by pulling the wet triangles several times through my fingers.Owing to the slime from the worms' bodies, the dirt was not easily washed off.We may therefore conclude that if a triangle, before being dragged in by the apex, had been dragged into a burrow by its base with even a slight degree of force, the basal part would long retain its creases and remain dirty.The condition of 89 triangles (65 narrow and 24 broad ones), which had been drawn in by the apex, was observed; and the bases of only 7 of them were at all creased, being at the same time generally dirty.Of the 82 uncreased triangles, 14 were dirty at the base; but it does not follow from this fact that these had first been dragged towards the burrows by their bases; for the worms sometimes covered large portions of the triangles with slime, and these when dragged by the apex over the ground would be dirtied; and during rainy weather, the triangles were often dirtied over one whole side or over both sides.If the worms had dragged the triangles to the mouths of their burrows by their bases, as often as by their apices, and had then perceived, without actually trying to draw them into the burrow, that the broader end was not well adapted for this purpose--even in this case a large proportion would probably have had their basal ends dirtied.We may therefore infer--improbable as is the inference-- that worms are able by some means to judge which is the best end by which to draw triangles of paper into their burrows.
The percentage results of the foregoing observations on the manner in which worms draw various kinds of objects into the mouths of their burrows may be abridged as follows:-Drawn into the Drawn in, Drawn in, Nature of Object.burrows, by or by or by or near near near the the the apex.middle.base.Leaves of various kinds 80 11 9 - of the Lime, basal margin of blade broad, apex acuminated 79 17 4 - of a Laburnum, basal part of blade as narrow as, or some- times little narrower than the apical part 63 10 27 - of the Rhododendron, basal part of blade often narrower than the apical part 34...66 - of Pine-trees, consisting of two needles arising from a commonbase......100 Petioles of a Clematis, somewhat pointed at the apex, and blunt at the base 76...24 - of the Ash, the thick basal end often drawn in to serve as food 48.5...51.5 - of Robinia, extremely thin, especially towards the apex, so as to be ill-fitted for plugging up the burrows 44...56 Triangles of paper, of the two sizes 62 15 23 - of the broad ones alone 59 25 16 - of the narrow ones alone 65 14 21If we consider these several cases, we can hardly escape from the conclusion that worms show some degree of intelligence in their manner of plugging up their burrows.Each particular object is seized in too uniform a manner, and from causes which we can generally understand, for the result to be attributed to mere chance.That every object has not been drawn in by its pointed end, may be accounted for by labour having been saved through some being inserted by their broader or thicker ends.No doubt worms are led by instinct to plug up their burrows; and it might have been expected that they would have been led by instinct how best to act in each particular case, independently of intelligence.We see how difficult it is to judge whether intelligence comes into play, for even plants might sometimes be thought to be thus directed; for instance when displaced leaves re-direct their upper surfaces towards the light by extremely complicated movements and by the shortest course.With animals, actions appearing due to intelligence may be performed through inherited habit without any intelligence, although aboriginally thus acquired.Or the habit may have been acquired through the preservation and inheritance of beneficial variations of some other habit; and in this case the new habit will have been acquired independently of intelligence throughout the whole course of its development.There is no a priori improbability in worms having acquired special instincts through either of these two latter means.Nevertheless it is incredible that instincts should have been developed in reference to objects, such as the leaves of petioles of foreign plants, wholly unknown to the progenitors of the worms which act in the described manner.Nor are their actions so unvarying or inevitable as are most true instincts.