animal, whether they be constant or temporary ones. In order to display this property it is necessary that sensation should exist, and that this should be pleasurable or painful, in order to produce a determinate movement to increase the one or escape the other. This is the basis of all design, for without consciousness there can be no design. Just where this consciousness first displays or displayed itself in living things it is not possible to know at present with certainty, but its first exhibition was probably in the pain of hunger. The first designed act was, then, the taking of food. The first structure was, therefore, also some kind of arrangement for seizing and surrounding food. This having been performed, another set of functions had its birth, one which was destined to follow all new experiences, and in turn to dominate all later acts. This is the memory of the act and of its consequences, which remains as the basis of mind. An impress once, made on consciousness is not lost,
Fig. 8.—Cast of Brain-Cavity of Phenacodus primævus, showing small hemispheres: a, side; b, from above; c, from below. One half natural size. (From Wyoming) because it has modified the molecular structure of some part of the living material in a way as yet unknown to a us. The movement which results from this memory is the first designed act, and this also affects structure, and produces the first motor link between mind and body, as the first stimulus & perceived produced the first sensory link. From this time onward the law of use and effort has its way. Its first result is to build a mind-machine, or nervous system, or its equivalent. This kind of building has evidently preceded all others in time, and its latest and highest product is the human brain. The evidence of vertebrate paleontology places this statement beyond the stage of mere hypothesis. We have learned that, with a few minor exceptions, the brains of the vertebrata, and especially of the mammalia, have greatly increased in complexity and in size with the lapse of geological time. This is illustrated by the accompanying figures of the brain-chambers or casts of brain-chambers of two ancient and one late Tertiary mammals. The Coryphodon elephantopus is the largest animal of the three, and the Phenacodus primævus, of which the skeleton was figured in the preceding article, is a little smaller than the Procamelus occidentalis, the third species. The last is the latest species in time, and is one of the ancestors of the existing camels and llamas. The much greater size and complexity of the brain, and especially of the cerebral hemispheres, as compared with the two other species, are striking.
