This novel situation is supposed to have come about as follows: In the remote past the Viceroy was a blue-and-black butterfly like its relatives, but because of the abiding principle of variation the individuals of the species were not exactly alike--some specimens were lighter than others. For some reason or other these lighter-colored butterflies had a slight advantage in the struggle for existence, and so in time the entire species was of this type, the darker specimens having been exterminated. Finally, some individuals chanced to bear a slight resemblance to distasteful butterflies of the Monarch type, so that birds avoided them, but continued to feed upon their less fortunate relatives. Thus, through a long process of natural selection, the Viceroy has come to resemble the Monarch. HELIOTROPISM AND LIST It was long ago observed that plants respond definitely and mechanically to the direction of rays of light; the leaves and flowers of many plants always turn toward the sun and even follow its daily course, so that the flower which turned to the East in the morning faces due West at sunset. Similar phenomena are now known to occur in animals. Among butterflies a good example is that of the Mourning Cloak (_Vanessa antiopa_). This butterfly, when it alights in the sunlight, almost invariably turns about until its body lies parallel with the rays of light and its head points directly away from the sun. This phenomenon is known as _negative heliotropism_, and a number of plausible explanations of it have been advanced. Probably it is merely another method of blending with the background, akin to protective coloration. When the Mourning Cloak alights upon the ground, or upon a log, it closes its wings and becomes well-nigh indistinguishable from its surroundings, because the under side of the wings is protectively colored. Now, if the body lies at right angles to the sun’s rays, the wings cast a large shadow, much more conspicuous than the butterfly itself, and hence attracting unfriendly eyes to the butterfly. If however the body is in line with the rays of light, and the wings brought together vertically, the shadow is insignificant. One has only to pin a few dead butterflies on a smooth neutral background in full sunlight to see the force of this theory. It is very probable, then, that _negative heliotropism_ is simply a method of reducing the too-conspicuous shadow to its lowest terms. Other butterflies reduce the shadow by what is known as _list_, leaning far over to one side like a sail-boat in a storm--hence the name. The best American example of _list_ is found in the behavior of the Wood-nymph butterfly (_Satyrus alope_), which is often seen to topple over to one side, presenting the entire wing surface to the source of light, lowering the top-line and thus reducing the shadow. FEIGNING DEATH