136. Suppose, for the sake of illustration, we regard an Orchestra in the light of the Development Hypothesis. The various instruments of which it is composed have general resemblances and particular differences, not unlike those observable in various organisms; and as we proceed in the work of classification we quickly discover that they may be arranged in groups analogous to the Sub-kingdoms, Classes, Orders, Genera, and Species of the organic world. Each group has its cardinal distinction, its initial point of divergence. All musical instruments resemble each other in the fundamental character of producing Tone by the vibrations of their substance. This may be called their organic basis. The first marked difference which determines the character of two sub-kingdoms (namely, instruments of Percussion and Wind instruments) arises from a difference in the method of impressing the vibrations; and the grand divisions of these sub-kingdoms arise from the nature of the vibrating substances. Each type admits of many modifications, but the primary distinction is ineffaceable. We can conceive the Pipe modified into a Flute, a Flageolet, a Clarionet, a Hautbois, a Bassoon, or a Fife, by simple accessory changes; to modify the Pipe into a Trumpet, and thus produce the peculiar _timbre_ of the trumpet, would be impossible except by the _substitution_ of a new material; by replacing the wood with metal we may adhere to the old Type, but we have created a new Class. (Attention is requested to this point, because the current views respecting the transmutation of tissues, which seem to lend a decisive support to the hypothesis of the transmutation of species are very commonly vitiated by the confusion of transformation with substitution. No anatomical element is _transformed_ into another specifically different--an epithelial-cell into a nerve-cell, for instance--but one anatomical element is frequently _substituted_ for another.) To convert the Pipe or the Trumpet into a Violin or a Drum would be impossible. We can follow the modifications of a Tambourine into a Drum or Kettle-drum, but no modifications of these will yield the Cymbals. That is to say, the vibrating materials--wood, metal, parchment, and the combination of wood and strings--have peculiar properties, and the instruments formed of such materials must necessarily from the very first belong to different groups, each subdivision of the groups being dependent on some characteristic difference in methods of impressing the vibrations, or in the materials. Although all musical instruments have a common property and a common purpose, we do not regard them as transformations of one primitive instrument; their kindred nature is a subjective conception; the analogies are numerous and close, but we know their origin. It is obvious that men being pleased by musical tones, have been led by their delight to construct instruments whenever they have