But we enter on the subject of conduct when we begin to study such combinations among the actions of sensory and motor organs as are externally manifested. Suppose that instead of observing those contractions of muscles by which the optic axes are converged and the foci of the eyes adjusted (which is a portion of physiology), and that instead of observing the co-operation of other nerves, muscles and bones, by which a hand is moved to a particular place and the fingers closed (which is also a portion of physiology), we observe a weapon being seized by a hand under guidance of the eyes. We now pass from the thought of combined internal functions to the thought of combined external motions. Doubtless, if we could trace the cerebral processes which accompany these, we should find an inner physiological co-ordination corresponding with the outer co-ordination of actions. But this admission is consistent with the assertion, that when we ignore the internal combination and attend only to the external combination, we pass from a portion of physiology to a portion of conduct. For though it may be objected that the external combination instanced is too simple to be rightly included under the name conduct, yet a moment's thought shows that it is joined with what we call conduct by insensible gradations. Suppose the weapon seized is used to ward off a blow. Suppose a counter-blow is given. Suppose the aggressor runs and is chased. Suppose there comes a struggle and a handing him over to the police. Suppose there follow the many and varied acts constituting a prosecution. Obviously the initial adjustment of an act to an end, inseparable from the rest, must be included with them under the same general head; and obviously from this initial simple adjustment, having intrinsically no moral character, we pass by degrees to the most complex adjustments and to those on which moral judgments are passed. Hence, excluding all internal co-ordinations, our subject here is the aggregate of all external co-ordinations; and this aggregate includes not only the simplest as well as the most complex performed by human beings, but also those performed by all inferior beings considered as less or more evolved. § 4. Already the question: What constitutes advance in the evolution of conduct, as we trace it up from the lowest types of living creatures to the highest? has been answered by implication. A few examples will now bring the answer into conspicuous relief.