In higher forms of life, on the contrary, such as vertebrate animals and civilized communities, the elementary parts are sufficiently diverse to be interwoven into highly individual and compact organisms. The variety of the atoms or molecules makes possible a great solidarity in the molar unit they compose, since the uniqueness and indissolubility of a structure is directly proportionate to the diversity of the elements that compose it. A man, if he is to attain the dignity of manhood, must be more than a stomach; he must knit into his single unity a bony skeleton, a circulatory system, a brain and nervous apparatus, complicated viscera, and heart, mind, and spirit. A state depends for its vitality on the varied characters and abilities of its citizens; it must have laborers, artisans, merchants, sailors, soldiers, students, and statesmen. In the second book of his “Republic,” Plato describes the differentiation of talents and pursuits in the citizens on which depends the advance in civilization of the society. Such an increase in differentiation of the parts, accompanied by increasing definiteness and coherence in the wholes, characterizes every process of evolution. The history of music is the history of such an evolution. Music began with vague, unlocated sounds, not combined with one another, but following at haphazard, and but slightly contrasted in pitch or duration. Gradually, under the inconceivably slow yet irresistible influence of men’s selective and constructive faculty, these sounds took on definiteness, were fixed in pitch, were measured in time, were knit into phrases and themes as words are knit into sentences, were combined simultaneously in chords as individuals are combined in communities;--became, in a word, the various, clearly defined, and highly organized family of tones we use in modern music. Two passages from Spencer’s “First Principles” will bring before us very clearly the advance music has made towards heterogeneity in its elements, on the one hand, and towards definiteness and coherence in its wholes, on the other. “It needs,” he says, “but to contrast music as it is with music as it was, to see how immense is the increase of heterogeneity. We see this ... on comparing any one sample of aboriginal music with a sample of modern music--even an ordinary song for the piano; which we find to be relatively highly heterogeneous, not only in respect of the varieties in the pitch and in the length of the notes, the number of different notes sounding at the same instant in company with the voice, and the variations of strength with which they are sounded and sung, but in respect of the changes of key, the changes of time, the changes of timbre of the voice, and the many other modifications of expression: while between the old monotonous dance-chant and a grand opera of our own day, with its endless orchestral complexities and vocal combinations, the contrast in heterogeneity is so extreme that