EXPERIMENTAL MORPHOGENESIS 155 



We know already that the branchial apparatus of this form 

 is typically harmonious-equipotential, but it is complex- 

 equipotential too, for it also may regenerate what is wanting 

 in the proper way, by a budding from the wound ; and the 

 same is true of many other cases, the flatworm Planaria for 

 instance. 



Another type of systems, which might be said to be of 

 a higher degree, is exhibited in some very strange phenomena 

 of regeneration. It was first shown most clearly by some 

 experiments of Godlewski's that a whole tail may be 

 regenerated from a wound inflicted on the body of a 

 newt, even if this wound involves section of only a 

 portion of the body-diameter. Section of the whole of the 

 body-diameter of course would cause the formation of the 

 whole tail also ; but it was found that even an incomplete 

 cross-section of the body is capable of performing the whole 

 on a smaller scale. The series of possible cross-sections 

 which are all capable of regeneration would have to be 

 called a system of the complex type in this case ; but, 

 now we learn that every single cross-section is of the 

 harmonious type, we must speak of complex -harmonious 

 systems. What we have described is not the only in- 

 stance of our new type of morphogenetic systems. Some 

 other instances had been discovered a few years earlier, 

 though nobody had pointed out their true significance. 

 In the flatworm Planaria a partial cross-section is also 

 capable of forming a whole structure, say a head, and 

 all cases of so-called " super -regeneration ' after the 

 infliction of a complicated wound probably belong here 

 also. 



You may say that our two additions to the theory of 



