1 82 Regeneration 



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 super- 

 natural 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 trans- 

 parent. 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 



