Page:Popular Science Monthly Volume 7.djvu/64

54 centipede as the representative of a dawning instinct and its appropriate manifesting organ, the sensorium, it was found that reflex action, characteristic of acephalous animals, did not cease when the head and its special ganglia appeared, but that a large share of its actions was still purely reflex in character, even those prompted by its small and imperfect sensorium being but little raised above the reflex and into the region of instinctive actions; and that the ganglionic system and reflex action were continued all through the higher mollusks and the whole series of articulates, only diminishing in importance as the sensorium and instinctive action increased. So in the commencing vertebrate series, we find the nervous organization of the preceding races continued—that for reflex action being represented in the spinal cord, and that for instinctive action being continued in the sensorium; not only so, but in proportion as the cerebrum remains small and undeveloped, and the sensorium predominates, do instinctive actions remain in the ascendant both in number and importance. This is found to be true in all the lower orders of vertebrates—fishes and reptiles; and even in the lower mammalians, although the cerebrum may outweigh the other portions of the brain, still a very important part of the actions manifested is instinctive. As an example of this in birds.



may be mentioned the chick, which breaks its prison of shell with its beak and immediately runs about, sees and picks up its particle of food with unerring certainty without teaching or experience, hears and answers the call of the mother-bird, and scrambles toward her for protection although it may never have seen her. Birds also possess in a remarkable degree the impulse, akin to that of insects, for preparing elaborate habitations; but unlike the insect races they add a certain degree of intelligence to their work, varying it in form and material according to locality and surroundings, and even finishing for their own use that which others had left incomplete and abandoned. In proportion as instinct ceases to predominate, the work becomes less uniform; and so it may be observed in general, that in proportion as the habits of a given race are fixed and automatic, does each individual conform in its action to that prearranged method, and we know what each individual under given circumstances will do; but, as