There are grounds for believing that the luminescence of some of these insects serves them not to attract one another, but to scare would-be predatory foes, such as birds, bats, and reptiles. I have heard a story (which I should like to have confirmed) that in some part of tropical Asia a certain kind of bird collects half a dozen or so of a species of glow-worm and places them at the entrance to its nest, so as to scare nocturnal animals which might attack its eggs or its young. It is a noteworthy fact that a point of light in the dark may act in two opposite ways on animals which see it--either it attracts or it repels them. The physiologist calls this positive and negative "photo-taxis" (light-guidance). And we have the similarly positive and negative influence of chemical taste and smell, called "chemo-taxis," and a similarly contrasted positive and negative "hygrotaxis," or directive influence of moisture upon the movements of animals and plants. CHAPTER XXVI FROM APE TO MAN THE recent discoveries of the actual bones of very early races of man raise again a general interest in the inquiry as to what are the actual differences of structure between men and apes, and what were probably the steps by which, as the result of "survival of the fittest," some early man-like apes became ape-like men. The question also arises as to how long ago the transition actually took place, and whether it was a very gradual or a rapid one. We are to-day in possession of some important facts bearing upon this inquiry which were unknown to Huxley when he wrote his ever-memorable essay on "Man's Place in Nature," and triumphantly closed the controversy between himself and Sir Richard Owen. That was nearly fifty years ago.