6. We have mentioned the ideas concerning a design, or “entelechy,” acting as a guide to the developing egg and have shown that this revival of Platonic and Aristotelian philosophy in biology was due to a misconception; namely, that the egg consisted of homogeneous material which was to be differentiated into an organism. For this supernatural task supernatural agencies seemed required. But we have seen that the unfertilized egg is already differentiated in a way which makes the further differentiation a natural affair. This idea of a quasi superhuman intelligence presiding over the forces of the living is met with in the field of regeneration, and here again it is based upon a misconception. The lens of the eye is formed in the embryo from the epithelium lying above the so-called optic cup (the primitive retina). Where this retina touches the epithelium the latter begins to grow into the cup, the ingrowing piece of epithelium is cut off and forms the lens, which probably under the influence of substances secreted by the optic cup becomes transparent. Certain animals like the salamander are able to form a new lens when the old one has been removed by operation, but the new lens is formed in an entirely different way; namely, from the upper edge of the iris. G. Wolf, who observed this regeneration used it to endow the organism with a knowledge of its needs; the idea of a Platonic preconceived plan or an Aristotelian purpose suggested itself. But it can be shown that the organism does in this case what it is compelled to do by its physical and chemical structure.