358 Information Storage and Neural Control 



to particular inhomogeneities, there will be a morphogenetic 

 action and internal structure will result. Some of you may not 

 remember the vast argument that occurred near the turn of the 

 century when the German zoologist Driesch shook apart the two 

 half cells of a fertilized egg. Normally, of course, one would become 

 the right side, say, of a frog and the other the left side; but after 

 separation, each became an intact frog with perfectly good right 

 and left sides. The outer cell surfaces exposed to pond water 

 developed skin in the proper fashion, but the medial surfaces, 

 which became backbone and nervous system when left stuck 

 together, now also developed skin. This phenomenon caused 

 Driesch to turn vitalistic and invoke guiding entelechies, but it 

 was explained decades later by the American zoologist Child in 

 terins of concentration gradients from outside to center. In the 

 intact embryos the medial cell surfaces are at the low or high 

 end of a gradient of oxygen, carbon dioxide, or any other sub- 

 stance that must diffuse from or into the environment; but in the 

 separated cells the end of the gradient has moved to the center 

 of each cell instead of the center of the double cell mass. So, 

 provided the cell is more than a sac of water and is able to respond 

 to different oxygen concentrations by different morphological 

 responses, the organized morphology results from these quantita- 

 tive changes imposed by the environment. 



The same sort of thing operates throughout embryonic develop- 

 ment. With further cell divisions the germ layers become differ- 

 entiated and then organs are specified. Often it is only a matter 

 of minutes between the appearance of the endoderm and the 

 irrevocable commitment of a given endoderm cell to become a 

 bit of liver or of gut. In tliis particular case we know what the 

 environmental determiner is: if the cell is near heart, it becomes 

 liver; if not, it becomes gut. So environmental influences operate 

 all the way through ontogenesis, in gated time periods, to produce 

 firm outcomes. 



We are thoroughly familiar with this in many other areas as 

 well. We can tell what kind of environment a person has lived in 

 if he has thick soles or horny hands or a weathered face. Frown 

 or smile wrinkles are inorphological consequences of oft-repeated 

 behaviors. In this case, the environment of the skin is internal to 



