Huxley graphically describes the actions of a frog from which the cerebral hemispheres have been removed. “If that operation,” he says,[192] “is performed quickly and skilfully, the frog may be kept in a state of full bodily vigour for months, or it may be for years; but it will sit unmoved. It sees nothing; it hears nothing. It will starve sooner than feed itself, although food put into its mouth is swallowed. On irritation, it jumps or walks; if thrown into water it swims. If it be put on the hand it sits there, crouched, perfectly quiet, and would sit there for ever. If the hand be inclined very gently and slowly, so that the frog would naturally tend to slip off, the creature’s fore paws are shifted on to the edge of the hand, until he can just prevent himself from falling. If the turning of the hand be slowly continued, he mounts up with great care and deliberation, putting first one leg forward and then another, until he balances himself with perfect precision on the edge; and if the turning of the hand is continued, he goes through the needful set of muscular operations, until he comes to be seated in security on the back of the hand. The doing of all this requires a delicacy of co-ordination and a precision of adjustment of the muscular apparatus of the body which are only comparable to those of a rope-dancer.”
Now, why have we entered into these details? To reinforce, from a somewhat different point of view, that which has again and again been urged in the preceding sections of this inquiry, that much of animal behaviour is an organic legacy. A going mechanism of great delicacy, with ready-made co-ordinations, the products of biological evolution, affords to consciousness a vast body of its primary data. As Dr. Sherrington himself says,[193] “co-ordination is abundantly shown to result from the independent power of the spinal arcs, altogether apart from the influence of the great cranial sense-organs, and of the cerebral arcs superposed upon them. These senses and the brain find the elementary co-ordination of the skeletal musculature an achievement already provided and to hand in the spinal cord. And no doubt the product of the instrument is, with the instrument itself, given over to their use in the reactions they elicit from the spinal musculature.” We have seen how instinctive behaviour, in those animals in which it is best studied, affords in hereditary biological outline, a sketch which subsequent acquisition, under experience, serves only to elaborate by the filling in of details and of the more delicate shading in behaviour. But in the higher animals, in which a period of youth is a time for the acquisition of experience--for experimentation and practice,--it might seem that the inherited biological legacy was of less importance. The “spinal animal,” as Dr. Sherrington calls it,--that is, the animal in which the spinal centres are isolated from the cerebral centres--goes far to disprove any such view. In them the cerebral senses and the brain find elementary co-ordination of the bodily movements an achievement already provided and to hand in the spinal cord. But when different animals are compared--frog, bird, rabbit, dog, and monkey--the permanent effects of severance of brain connection, the effects which remain when the temporary period of disturbing “shock” is over, are more marked in the higher than the lower types. And concerning this, Dr. Sherrington says,[194] “The deeper depression of reaction into which the higher animal, as contrasted with the lower, sinks when made spinal, appears to me significant of this, that in the higher types, more than in the lower, the great cerebral senses actuate the motor organs, and impel the motions of the individual.”