Ascending from visceral actions to muscular and nervous actions, we find the correspondence displayed in a manner still more obvious. Every act of locomotion implies the expenditure of certain internal forces, adapted in amounts and directions to balance or out-balance certain external forces. The recognition of an object is impossible without a harmony between the changes constituting perception, and particular properties co-existing in the environment. Escape from enemies implies motions within the organism, related in kind and rapidity to motions without it. Destruction of prey requires a special combination of subjective actions, fitted in degree and succession to overcome a group of objective ones. And so with those countless automatic processes constituting instincts. In the highest order of vital changes the same fact is equally manifest. The empirical generalization that guides the farmer in his rotation of crops, serves to bring his actions into concord with certain of the actions going on in plants and soil. The rational deductions of the educated navigator who calculates his position at sea, form a series of mental acts by which his proceedings are conformed to surrounding circumstances. Alike in the simplest inferences of the child and the most complex ones of the man of science, we find a correspondence between simultaneous and successive changes in the organism, and co-existences and sequences in its environment. § 29. This general formula which thus includes the lowest vegetal processes along with the highest manifestations of human intelligence, will perhaps call forth some criticisms which it is desirable here to meet.