Sommering has observed, that man has the largest brain in proportion to the nerves given off from it; and that this proportional magnitude, may, in every instance, be referred to as the best criterion of the degrees of intelligence. Now, it appears to me not at all difficult to account for this fact (the general truth of which may be granted), by comparing it with another not less important, viz. that, in the inferior classes of animals, the nervous system becomes, as you descend, more and more widely diffused. Hence, I deduce this important principle, viz. that the degrees of intellect are, in all animals, in exact proportion to the concentration of the nervous system. Now, the more equally distributed this system is, the more independent of each other are the parts of organized beings, or, in other words, the necessity of a connection of these parts increases, in proportion to the magnitude of the common trunk compared with the rami. It is only, therefore, in the more perfect animals, that the connection of the different parts of the nervous system, and particularly the presence of central parts, is necessary to the existence of the different functions. Animals, on the contrary, having this sensitive substance very generally diffused, when mutilated, recover their figure, or, when cut into pieces, form several individuals, having each a system of sensation and volition. The larger warm-blooded animals acquire pieces of flesh analogous to those which have been cut away; crabs acquire new claws; the tadpoles of frogs and water newts acquire new limbs and tails; and the lower end of the snail, having been divided from the upper, acquires a new head. The earth and boatworm, when divided into considerable pieces, form several new individuals; but animals having this system still more generally diffused, as the polypus, when divided into the smallest fragments, each fragment self-exists and becomes a perfect individual. This also is more or less the case with plants. As you descend among them, their parts become less dependent on each other. The dicotyledons, which possess irritability, sleep and the principle of life most diffused, and which, among plants, are analogous to the dicordated animals, namely quadrupeds and birds, possess concentric fibres and the most diffused sensibility; the monocotyledons, analogous to the monocordated animals, namely reptiles and fishes, possess more numerous centers and less diffused sensibility; and the acotyledons, analogous to the acordated animals, possess most numerous centers and least diffused sensibility.