EFFECTS OF DARKNESS. On the other hand, the absence of light, or a life in perpetual darkness, has gravely modified the visual organs of cave animals and those living in the abysses of the sea. (See CAVE ANIMALS.) In the case of the blind beetles, crawfish, spiders, myriapods, etc., of caverns, we have the most obvious facts show ing the direct action of environment. The members of the fauna of our caves have their eyes variously affected: some are blind, others have vestiges of eyes, and others are completely eyeless. The cause is simply the result of disuse, for natural selection does not operate in such eases. The loss of eyesight and scanty food renders the body slender, pale, colorless, while in compensation for the loss of sight, the tactile Sense is greatly exalted; the antenme, legs, and other appendages are remarkably long and slen der compared with those of their out-of-doors relatives. The whole subject of cave life affords
a most instructive example of the effects of the absence of light, the disuse of organs and their different degrees of atrophy, and other remark able modifications of the body, and of use-inheri tance, all brought about by the action of the primary factors of evolution, without the inter vention of uritural selection. It is proper to say, however, that Weissman and other ardent Dar winians account for the facts by natural selec tion.
Other animals live in holes in the sea-bot tom, as some blind crustaceans and fishes, whose eyes in the very young are normal, also toward or at maturity become blind, and perhaps eyeless. The blind fishes, and crustaceans of the deep sea afford similar instances. It is a significant fact that those animals, notably the fishes, are pro vided with phosphorescent organs.