4. The influence of the whole on the parts is nowhere shown more strikingly than in the field of regeneration. It is known that pieces cut from the plant or animal may give rise to new growth which in many cases will restore somewhat the original organism. Instead of asking what is the cause of this so-called regeneration we may ask, why the same pieces do not regenerate as long as they are parts of the whole. In this form the mysterious influence of the whole over its parts is put into the foreground. We shall see that growth takes place in certain cells when certain substances in the circulation can collect there. The mysterious influence of the whole on these parts consists often merely of the fact that the circulating specific or non-specific substances--we cannot yet decide which--will in the whole be attracted by certain spots and that this will prevent them from acting on other parts of the organism. If such parts are isolated the substances can no longer flow away from these parts and the parts will begin to grow. It thus becomes utterly unnecessary to endow such organisms with a “directing force” which has to elaborate the isolated parts into a whole. 5. The same difficulty which we have discussed in regard to morphogenesis exists also in connection with those instincts which preserve the life of the organism and of the race. The reader need only be reminded of all the complicated instincts of mating by which sperm and eggs are brought together; or those by which the young are prevented from starvation to realize the apparently desperate problems in store for a mechanist, to whom the assumption of design is meaningless. And yet we are better off in regard to our knowledge of the instincts than we are in regard to morphogenesis, as in the former we can show that the apparent instincts in some cases obey simple physicochemical laws with almost mathematical accuracy. Since the validity of the law of gravitation has been proved for the solar system the idea of design in the motion of the planets has lost its usefulness, and this fact must serve us as a guide wherever we attempt to put science beyond the possibility of mysticism. As soon as we can show that a life phenomenon obeys a simple physical law there is no longer any need for assuming the action of non-physical agencies. We shall see that this has been accomplished for one group of animal instincts; namely those which determine the relation of animals to light, since these are being gradually reduced to the law of Bunsen and Roscoe. This law states that the chemical effect of light equals the product of intensity into duration of illumination. Some authors object to the tendency toward reducing everything in biology to mathematical laws or figures; but where would the theory of heredity be without figures? Figures have been responsible for showing that the laws of chance and not of design rule in heredity. Biology will be scientific