When we see in a living body thousands of cells working together to a common end, dividing the task between them, living each for itself at the same time as for the others, preserving itself, feeding itself, reproducing itself, responding to the menace of danger by appropriate defensive reactions, how can we help thinking of so many instincts? And yet these are the natural functions of the cell, the constitutive elements of its vitality. On the other hand, when we see the bees of a hive forming a system so strictly organized that no individual can live apart from the others beyond a certain time, even though furnished with food and shelter, how can we help recognizing that the hive is really, and not metaphorically, a single organism, of which each bee is a cell united to the others by invisible bonds? The instinct that animates the bee is indistinguishable, then, from the force that animates the cell, or is only a prolongation of that force. In extreme cases like this, instinct coincides with the work of organization.
Of course there are degrees of perfection in the same instinct. Between the humble-bee, and the honey-bee, for instance, the distance is great; and we pass from one to the other through a great number of intermediaries, which correspond to so many complications of the social life. But the same diversity is found in the functioning of histological elements belonging to different tissues more or less akin. In both cases there are manifold variations on one and the same theme. The constancy of the theme is manifest, however, and the variations only fit it to the diversity of the circumstances.
Now, in both cases, in the instinct of the animal and in the vital properties of the cell, the same knowledge and the same ignorance are shown. All goes on as if the cell knew, of the other cells, what concerns itself; as if the animal knew, of the other animals, what it can utilize--all else remaining in shade. It seems as if life, as soon as it has become bound up in a species, is cut off from the rest of its own work, save at one or two points that are of vital concern to the species just arisen. Is it not plain that life goes to work here exactly like consciousness, exactly like memory? We trail behind us, unawares, the whole of our past; but our memory pours into the present only the odd recollection or two that in some way complete our present situation. Thus the instinctive knowledge which one species possesses of another on a certain particular point has its root in the very unity of life, which is, to use the expression of an ancient philosopher, a "whole sympathetic to itself." It is impossible to consider some of the special instincts of the animal and of the plant, evidently arisen in extraordinary circumstances, without relating them to those recollections, seemingly forgotten, which spring up suddenly under the pressure of an urgent need.