REGENERATION 



323 



(1942), that the regenerate from the proximal surface forms the whole 

 missrng region and not only a part of it (Fig. 14.7). We can conclude 

 therefore that regeneration will always produce the whole missing region 

 from the cut surface to the distal tip of the organ, even if this means that a 

 reversal of polarity has to occur at the place where the cut was made It 

 may be pointed out that if a section of a limb is removed and the distal 

 region grafted back on to the stump, no regeneration of the missing seg- 

 ment occurs, probably because there is no opportunity for a blastema to 

 rorm. 



i^^V;^: b 





Figure 14.7 



(Left) Part of an anterior limb of a newt, consisting of sections of the'humcr- 

 us, and of the radius and uba, was grafted into the flank. Both ends have 

 regenerated and each blastema has produced all the structures distal to the 

 position of the wound from which it arose. (From Monroy 1942.) 

 Kl^ JT ^"^.b-^,^^,f g^^^^^^es (. and b), and one {c) showiiag features 

 of both tail and limb, all from axolotl tails onto which limb-skin has been 

 transplanted. (From Luther 1948.) 



Regeneration, of the limb at least, is not only limited by the fact that it 

 proceeds only distally and never proximally: it can also not proceed 

 laterally That is to say, if a limb is spht longitudinally and one half re- 

 moved, this half IS not replaced. However, if the half-limb is now ampu- 

 tated regeneration occurs and the regenerated portion of the hmb is 

 complete m cross-section. Similarly, if one of the long bones of a hmb is 

 removed, it will not be regenerated, but if the hmb is now amputated 



