Among the crystals termed _isomorphous_ by chemists, the dominant ingredient which is common to them all, controls the form, but difference of size answers sufficiently to the partial unlikeness of the other less active elements; and so in the instances of cubes and octahedrons formed of dissimilar minerals where difference of constitution is indicated by varied dimensions only. VII. Crystal and crystal, and, drop and drop, are alike within the limits of the species, or their unlikeness, if there be any, is not appreciable to our senses, and scarcely conceivable though not absolutely impossible to thought; but we know certainly that clear individuality of character is everywhere pursued and marked by peculiarity of form and size throughout the entire universe. While among minerals and fluids dissimilarity occurs obviously only between species, among plants it begins to be conspicuous between individuals, growing more and more so as observation ascends in the vegetable kingdom. Two stalks of grass may resemble each other as much as two crystals of the same salt, but timber trees grow more unlike, and fruit trees differ enough to make their identification comparatively easy. But it is in the animal kingdom, eminently, and with increasing distinctness as the rank rises, that individuals become distinguishable from each other; for it is here that diversity of character gets opportunity, from complexity of nature, freedom of generating laws, and varied influence of circumstances, to impress dissimilarity deepest and clearest. Crystals undergo no modification of state but instant formation and the sudden violence which destroys them. Vegetables pass through the changes of germination and growth, and feel the difference of soil, and winds, and temperature, and to the limits of these influences, confess them in color, size, and shape; but animals, endowed with acuteness of sense, enjoying locomotion, and related to all the world around them—living in all surrounding nature, and susceptible of all its influences—their individual differences know no limits, and they are universally unlike in appearance as in circumstances, training and character. Even in the lower orders there is ample proof of this. The mother bird and beast know their own young; the shepherd and the shepherd’s dog know every one of their own flock from every other on all the hills and plains; and among the millions of men that people the earth, a quick eye detects a perfectly defined difference as broad as the peculiarity of character which underlies it. _Narrowness of relations and Simplicity of function are as narrowly restrained in range of conformation; Complexity makes proportionate room for difference; and Variety is the result, the sign, and the measure of Liberty._