LIFE AND MECHANISM. 29 tongue. There appears to be ever} 7 reason to suppose that in the case of the frog we have to deal with a mechanism, just as in the case of the Parainoaciuni ; though in the frog this mechanism must be assumed to be much more delicate and complicated. The step from the frog to man is scarcely so great as that from the Paramcecium to the frog. So far, then, as the facts have been examined, they seem entirely consistent with the hypothesis that the organism is only a machine so peculiarly constructed as to be capable of keeping itself in action automatically. But there is another point of difference between an organ- ism and an ordinary machine. This lies in the power which the organism possesses of adapting its actions to unusual circumstances. What I mean is well illustrated by the experiments which Darwin made with a view to testing the intelligence of earthworms. Earthworms are in the habit of stopping up the mouths of their burrows with leaves, leaf-stalks, or other convenient materials. It is evident that some leaves can be most con- veniently dragged into a burrow by their tip, while in the case of others of a different shape it will be more convenient to make use of some other part, as the stalk. Consequently, in laying hold of one part rather than another, the animal may display more or less intelligence. In order to exclude the hypothesis that a special 'inherited instinct determines the worms to select the most convenient part of each special kind of leaf, Darwin tested them with leaves of foreign trees, and triangles of paper. At the end of the account of his observations he says (Vegetable Mov.U, V.Y.C., p. 98) : " To sum up, as chance does not determine the manner in which objects are drawn into the burrows, and as the existence of specialised instincts for each particular case cannot be admitted, the first and most natural supposi- tion is that worms try all methods until they at last succeed ; but many appearances are opposed to such a supposition. One alternative alone is left, namely that worms, although standing low in the scale of organisation, possess some degree of intelligence. This will strike every one as impro- bable ; but it may be doubted whether we know enough about the nervous in of the lower animals to justify our natural distrust of such a con- clusion. With respect to the small size of the cerebral ganglia, we should remember what a mass of inherited knowledge, with some power of adapting means to an end, is crowded into the minute brain cf a worker-ant" In these experiments the worms display intelligence in the fact that they do not mechanically employ one constant means in dragging objects into their burrows, but tend to use just the particular means suited to the particular circum- stances of each case. That is to say, the intermediate steps in the process are in each particular case determined with reference to the final result. Hence we cannot simply say
