evolve colour; and that a noctiluca, or a luminous centipede, or a firefly, should produce light, ought not to seem more wonderful than that a plant should produce blue or purple flowers. But the biological interpretation of the phenomenon leaves me wondering, just as much as before, at the particular miracle of the machinery by which the light is made. To find embedded in the body of the insect a microscopic working-model of everything comprised under the technical designation of an "electric plant," would not be nearly so wonderful a discovery as the discovery of what actually exists. Here is a firefly, able, with its infinitesimal dynamo, to produce a pure cold light "at one four-hundredth part of the cost of the energy expended in a candle flame"!………Now why should there have been evolved in the tail of this tiny creature a luminiferous mechanism at once[1] so elaborate and so effective that our greatest physiologists and chemists are still unable to understand the operation of it, and our best electricians impotent to conceive the possibility of imitating it? Why should the living tissues crystallize or build themselves into structures of such stupefying[2] intricacy and beauty as the visual organs of an ephemera, the electrical organs of a gymnotus,[3] or
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