If this interpretation of Spencer, which Darwin expanded, were true, the consequences would be, that in the long succession of generations animals would have gradually rid themselves of that which is injurious and fatal to them. But this law does not verify itself in the least, rather do we see, in studying violent emotions, that the more serious the danger the greater is the predominance both in number and strength of injurious phenomena. We have already seen that trembling and cataplexy render us unable to flee or defend ourselves, and we shall now be convinced that in critical moments we see less distinctly than when we are tranquil. In the face of these facts we must admit that not all phenomena of fear can be explained by the theory of selection. In their extreme degrees they are morbid phenomena indicating an imperfection of the organism. One might almost say that nature had not been able to find a substance for brain and spinal cord which should be extremely sensitive, and yet should never, under the influence of exceptionally strong stimuli, exceed in its reaction those physiological limits which are best adapted to the preservation of the animal. But before we go further, let us consider those facts which seem to contradict the hypothesis of Spencer and Darwin. II We all know that the pupil through which the rays of light pass, in order to reach the posterior part of the eye, dilates and contracts with great facility. In the cat its form is variable; generally elliptic, it becomes in a strong light very narrow and nearly shut, appearing like a slit scarcely wider than a hair; towards evening, or in a dark place during the day, it dilates in such a manner that the iris nearly disappears, and one can see the greenish, phosphorescent background of the eye. The iris is like a circular curtain which closes in a strong light and opens in the dark, regulating automatically the amount of light necessary for sight without causing injury to the eye. The perfection of our machine is such, that some indispensable mechanisms not only work automatically, without any participation of the will or consciousness, but often also without needing either spinal cord or brain, as those few nerve-cells, found in the organs in the form of microscopic ganglia, suffice for the reflex movements. This harmony by which the body assures the performance of its most important functions, by putting in motion several mechanisms at the same time, all of which are directed to the same end, is worthy of meditation. The mechanism of these movements of the iris is very complicated; I have noticed that whenever the vessels dilate, the pupil contracts, and when the vessels contract, the pupil dilates.[22] [22] A. Mosso: _Sui movimenti idraulici dell’ iride_. R. Accademia di Torino, 1875.