Page:Principles of Psychology (1890) v1.djvu/99

79 FUNCTIONS OF TEE BRAIN. 79 All nervous centres have then in the first instance one essential function, that of 'intelligent' action. They feel, prefer one thing to another, and have 'ends.' Like all other organs, however, they evolve from ancestor to descend- ant, and their evolution takes two directions, the lower centres passing downwards into more unhesitating autom- atism, and the higher ones upwards into larger intellectu- ality.* Thus it may happen that those functions which can safely grow uniform and fatal become least accompanied by mind, and that their organ, the spinal cord, becomes a more and more soulless machine; whilst on the contrary those functions which it benefits the animal to have adapted to delicate environing variations pass more and more to the hemispheres, whose anatomical structure and attendant consciousness grow more and more elaborate as zoological evolution proceeds. In this way it might come about that in man and the monkeys the basal ganglia should do fewer things by themselves than they can do in dogs, fewer in dogs than in rabbits, fewer in rabbits than in hawks,f fewer in hawks than in pigeons, fewer in pigeons than in frogs, fewer in frogs than in fishes, and that the hemispheres should correspondingly do more. This passage of functions for- ward to the ever-enlarging hemispheres would be itself one of the evolutive changes, to be explained Hke the develop- ment of the hemispheres themselves, either by fortunate variation or by inherited effects of use. The reflexes, on this view, upon which the education of our human hemi- spheres depends, would not be due to the basal ganglia short spau of life does not give it time to learn the new tricks asked for. But Rosenthal (Biologisches Centralblatt, vol. iv. p. 347) and Mendelssohn (Berlin Akad. Sitzungsberichte, 1885, p. 107) in their investigations on the simple reflexes of the frog's cord, show that there is some adaptation to new conditions, inasmuch as when usual paths of conduction are interrupted by a cut, new paths are taken. According to Rosenthal, these grow more pervious (i.e. require a smaller stimulus) in proportion as they are more often traversed. acquired, or through the preservation of lucky variations, is an alternative which we need not discuss here. We shall consider it in the last chapter in the book. For our present purpose the modus operandi of the evolution makes no difference, provided it be admitted to occur. f See Schrader's Observations, loc. at.
 * Whether this evolution takes place through the inheritance of habits