"Nature never makes a leap," says the scientific investigator, as he studies the material symbols of thought. "Thought never makes a leap," says the metaphysician, as he studies the necessary laws of rational action: and both have uttered the same truth. We prove a proposition by determining the steps by which it was educed from a more generic statement. Science must proceed in the same manner, for science only discovers the track of mind--it does not make the track, it only follows it. If then we find the chain of evolution broken at any point, science must either stop there, or assume the wanting term in the series. We have the right to interpolate these missing terms, for we must assume that the thoughts of God communicated to us in material forms constitute a continuous revelation, beginning with Himself, the final generalization, and ending with man the highest individualization. These limits are fixed--the one by the nature of God, and the other by the nature of man. Between these two extremes we must find a series of intermediate terms. Any other conception of their relation than that of a determinate series is impossible and irrational; and a series, so far as it means anything, means evolution of some sort. Finding the relation between these terms--distinguishing the _same_ which reproduces itself, and the _different_ which introduces a new term--that is, determining the law of apparent evolution--is the problem presented to science. The astronomer found Bode's law to all appearance violated by the omission of a planet between Mars and Jupiter. He could see no reason for the law, but if the planets had been placed by an intelligent Creator, some order of arrangement must be discoverable according to which their position was determined. The Creator being intelligent, it is impossible to conceive them placed fortuitously. There must then be a link between Mars and Jupiter, because the law once established cannot be broken. The same law may be observed in the arrangement of leaves around the axis of a plant. If intelligence arranged them they must be arranged in some order, for intelligence never performs the least act without a purpose. Each leaf or pair of leaves is not a mere duplication of the previous leaf or pair of leaves. The relation which subsists between any two sets in the series expresses the idea of the Creator, and this must be constant. Completing the series as indicated by different plants, we may assume that if any term is apparently wanting, it is only because it has not been discovered. In neither of these cases would it be asserted that any physical evolution had taken place--the terms form a series of which each term is equally determined by the operation of a fixed law; and yet it is an operation precisely analogous to that which in the case of animals presents every appearance of a real evolution. Take, for instance, a series of animals, presenting at one