While this is not a case of increase in the particular organ, it illustrates a progressive series of steps whereby the organism becomes better adapted to its surroundings. A similar instance is found in the suppression of certain sets of organs in internal parasites. For illustration, the tapeworm loses particular organs of digestion for which it does not have continued use; but the reproductive organs, upon which the continuance of its life depends, are greatly increased. Such cases as the formation of short-winged beetles show us that the action of natural selection is not always to preserve what we should call the best, but simply to preserve the fittest. Development, therefore, under the guidance of natural selection is not always progressive. Selection by nature does not mean the formation and preservation of the ideally perfect, but merely the survival of those best fitted to their environment. Color.--The various ways in which natural selection acts are exceedingly diversified. The colors of animals may be a factor in their preservation, as the stripes on the zebra tending to make it inconspicuous in its surroundings. The stripes upon the sides of tigers simulate the shadows cast by the jungle grass in which the animals live, and serves to conceal them from their prey as well as from enemies. Those animals that assume a white color in winter become thereby less conspicuous, and they are protected by their coloration. As further illustrating color as a factor in the preservation of animals, we may cite a story originally told by Professor E.S. Morse. When he was collecting shells on the white sand of the Japanese coast, he noticed numerous white tiger-beetles, which could scarcely be seen against the white background. They could be detected chiefly by their shadows when the sun was shining. As he walked along the coast he came to a wide band of lava which had flowed from a crater across the intervening country and plunged into the sea, leaving a broad dark band some miles in breadth across the white sandy beach. As he passed from the white sand to the dark lava, his attention was attracted to a tiger-beetle almost identical with the white one except as to color. Instead of being white, it was black. He found this broad, black band of lava inhabited by the black tiger beetle, and found very few, if any, of the white kind. This is a striking illustration of what has occurred in nature. These two beetles are of the same species, and in examining the conditions under which they grow, it is discovered that out of the eggs laid by the original white forms, there now and then appears one of a dusky or black color. Consider how conspicuous this dark object would be against the white background of sand. It would be an easy mark for the birds of prey that fly about, and therefore on the white surface the black beetles would be destroyed, while the white ones would be left. But on the black background of lava the conditions are reversed.