It may seem more difficult to account for the willingness of Norka's three sisters to aid in his destruction--unless, indeed, the whole story be considered to be mythological, as its Indian equivalents undoubtedly are. But in many versions of the same tale the difficulty does not arise. The princesses of the copper, silver, and golden realms, are usually represented as united by no ties of consanguinity with the snake or other monster whom the hero comes to kill. In the story of "Usuinya,"[96] for instance, there appears to be no relationship between these fair maidens and the "Usuinya-Bird," which steals the golden apples from a monarch's garden and is killed by his youngest son Ivan. That monster is not so much a bird as a flying dragon. "This Usuinya-bird is a twelve-headed snake," says one of the fair maidens. And presently it arrives--its wings stretching afar, while along the ground trail its moustaches [_usui_, whence its name]. In a variant of the same story in another collection,[97] the part of Norka is played by a white wolf. In that of Ivan Suchenko[98] it is divided among three snakes who have stolen as many princesses. For the snake is much given to abduction, especially when he appears under the terrible form of "Koshchei, the Deathless." Koshchei is merely one of the many incarnations of the dark spirit which takes so many monstrous shapes in the folk-tales of the class with which we are now dealing. Sometimes he is described as altogether serpent-like in form; sometimes he seems to be of a mixed nature, partly human and partly ophidian, but in some of the stories he is apparently framed after the fashion of a man. His name is by some mythologists derived from _kost'_, a bone whence comes a verb signifying to become ossified, petrified, or frozen; either because he is bony of limb, or because he produces an effect akin to freezing or petrifaction.[99] He is called "Immortal" or "The Deathless,"[100] because of his superiority to the ordinary laws of existence. Sometimes, like Baldur, he cannot be killed except by one substance; sometimes his "death"--that is, the object with which his life is indissolubly connected--does not exist within his body. Like the vital centre of "the giant who had no heart in his body" in the well-known Norse tale, it is something extraneous to the being whom it affects, and until it is destroyed he may set all ordinary means of annihilation at defiance. But this is not always the case, as may be learnt from one of the best of the skazkas in which he plays a leading part, the history of-- MARYA MOREVNA.[101] In a certain kingdom there lived a Prince Ivan. He had three sisters. The first was the Princess Marya, the second the Princess Olga, the third the Princess Anna. When their father and mother lay at the point of death, they had thus enjoined their son:--"Give your sisters in marriage to the very first suitors who come to woo them. Don't go keeping them by you!"