Now these germs of life contain vital forces, sense powers, psychic powers, and ethereal particles of matter. At the time of death the soul contracts and withdraws all its powers from the sense organs to its innermost center, and in that contracted state it leaves the body. But these powers do not leave the soul. By the law of persistence of force and conservation of energy they remain latent in that center until environmental conditions become favorable for their remanifestation. Rebirth means the manifestation of the latent powers which exist in the germ of life or in the individual soul. These germs of life are called by different names. Leibnitz called them monads and modern scientists call them bioplasms or some such name, but the Vedanta philosophers describe them as subtle bodies. These germs or subtle bodies are subject to evolution and growth; they arise from lower to higher stages of development, from the mineral through the vegetable to the animal kingdom and eventually they become human beings and then they go on progressing. In the Platonic theory the idea of progress, growth or gradual evolution of the soul from the lower to higher stages of existence is entirely excluded, because, as I have already said, the migrating substance is of a fixed quantity with fixed qualities, that is, these qualities do not change and are not affected by either growth or evolution. They are constant quantities. In order to differentiate these two ideas we should call the Hindu theory of Transmigration by the term "Reincarnation." The Hindu or Vedantic theory of Reincarnation, however, is not the same as the Buddhistic theory of Rebirth, for the Buddhists do not believe in the permanence of the soul entity. There is another point where the Reincarnation theory differs from Platonic transmigration. According to this theory of Reincarnation there is growth and evolution of each individual soul from the lower to higher stages of development. The soul or germ of life, after passing through the lower stages, comes to the human plane and gains experience and knowledge; and after coming to the human plane, it does not retrograde to animal bodies. The Platonic theory teaches that human souls migrate into animal bodies or angelic bodies and return from the angelic to the human or the animal, and that some of them prefer to become animals; while the theory of Reincarnation, taking its stand upon the scientific truth of gradual evolution, teaches that the human souls have already passed through different grades of the animal, nay, of the vegetable kingdom, by the natural process of evolution. After having once received the human organism, why should a soul choose to go back to the lesser and more imperfect organism of an animal? How is it possible for a lesser manifestation to hold a greater one? Why should a greater manifestation choose more limited forms in preference to those of others? This question arises in the Platonic theory of Transmigration.