The trials of apprenticeship! Here we are, it seems, brought to Jennings's theory, which we have immediately judged to be untenable, at least in the cases and in the form in which it has been presented. But this contradiction is purely apparent. In this theory all the reactions to stimuli, from those of tropisms to the recoils and rotations of differential sensitiveness, represent a series of motor phenomena which are actually tried before adaptation; the animal is still an apprentice, trying to adapt itself. But it is not any more so with the relatively higher animals which we have chosen for example; the Littorinas and the caterpillar of the dunes show all the phenomena of tropisms and of differential sensitiveness, but the latter manifests itself by a precise directive modality, which leads immediately to the end and without trials ; the animal is no longer undergoing an apprenticeship, it is benefiting by a remote experience acquired by the species in the cours'e of its history in normal etiological conditions.
With most of the articulates, if not with all, the manifestations of differential sensitiveness in the normal conditions of its environment seem perfectly adapted. It is the same with the mollusks studied by Bohn. They are hardly so with the lower organisms upon which the delicate researches of Jennings were made. In Oxytricha fallax, for example, the infusorian executes its recoils and its rotations a number of times before reaching the favoring cold zone, but each time it comes nearer the latter, which indicates, perhaps, a beginning of adaptation and perhaps also gave birth to Jennings's theory.
But the articulates and the mollusks have a well-differentiated nervous system, a brain represented by a pair of ganglia, and sense organs connected with the brain ; while the Infusoria are reduced to a protoplasmic mass, complex, it is true, but in which the sensitiveness is diffused, without any nervous localization. If it is true, as the most precise experiments show, that sensations choose the brains as a center, and can produce there these durable impressions which characterize memory, we are led to see in the adaptations of differential sensibility one of the results (and perhaps also one of the causes) of the concentration of the nervous substance in a distinct system, a response by which the determined stimulating variations provoke determined movements, and not by others. It is the work of memory, not an individual memory, but a species memory, which has progressively developed from the origin of the species, and which, by heredity, manifests itself to-day in all representatives of the species.
Thus, species memory with the adaptation which it carries, presents a real development with the more or les»s superior animals, and remains in a rudimentary state with the more simple animals. But between these two extremes one sees all the intermediate steps in the concentration of the nervous system, and one should wait to observe all the degrees in the phenomena of differential adaptation and of species memory. This is why we refuse to see in these phenomena what we have seen in tropisms,-manifestations to which physiological selections seem strange. Natural selection has been working on all these beings, but it has collaborated here with an active adaptation by physiological selection (see page 42).
Before going further, it will be useful to cast a glance over the path so far pursued. Tropisms have shown us primitive phenomena by which the responses of living matter to stimuli manifest themselves. These responses are automatic, but not without suppleness, for they always combine more or less with the manifold activities which have their seat in all organisms, even the most simple. With the vital rhythms, we find ourselves in the presence of primitive and automatic phenomena, but by reason of their periodicity these phenomena have left a trace on the living matter, and they can be produced aside from the excitation which gave them birth. The living being has become the seat of an organic memory, which liberates it somewhat from the exterior environment ďand puts it on the path toward higher activities. With the species memory, we take the first steps on this path and penetrate into the domain of psychism, where the animal draws into the impressions of its nervous substance the power to act in one way rather than in another, the power of choice. It is true, we are still in full automatism, for this memory is bequeathed to the representatives of a species by remote ancestors in which it was born, and to-day shows itself in the individual by simple acts ; but it was in the beginning progressively acquired in the course of often fruitless experiments, and it represents the first beginnings of psychism. The lower organisms manifest their activity by tropisms, by rhythms, by the phenomena of differential sensibility, and we can hardly see in them gleams of species memory,-that is to say, of psychism. With the articulates, on the contrary, species memory plays a part which is not less great than the other responses to external stimuli, and psychism appears under the form of a new element, individual memory, which tends to take the predominant part in the entire activity of the being.
But before entering upon this new domain, we should study the so-called "simulation of death," which appears to be one of the most singular manifestations of differential sensibility.