REGENERATION OF THE LEG OF AMPHIUMA. 295 



cut off through the upper portion. In other words, no better 

 regeneration took place here than in the former instances. 



It is also of interest to notice that the other two legs that had 

 been cut off (close to the body) for examination had not regen- 

 erated. The skin grew over the cut surface, and in several cases 

 the muscles of the body wall seemed to have grown over the 

 short piece of the humerus or femur that had been left. At 

 most, a short protrusion indicated the position of the limb. 



How shall we interpret this result. Those who hold that the 

 power to regenerate a part is commensurate with the value of the 

 part to the animal, if it is a part liable to injury, will welcome this 

 experiment as in harmony with their interpretation. On the other 

 hand, as I have tried to show elsewhere, the evidence is so strong 

 against this point of view that I think we shall not go wrong if 

 in this case we deny that the result has any such meaning. 



In fact, in other adult amphibia, in the frogs for instance, in 

 which the limbs are of some importance to the animal they can- 

 not be regenerated, although in the tadpole stage in which the 

 limbs are of no importance, and, in the case of the fore -limb at 

 least, not liable to injury, the power of regeneration is present. 

 Moreover even in the urodeles the power of regeneration is un- 

 equally developed in forms that use their legs for purposes of 

 locomotion. It is said that Triton marnioratus shows only a 

 slight power to regenerate its legs. In other cases, as I have 

 observed in Nectiirus, the time required to regenerate a leg is so 

 long that were the presence of the leg essential to the existence 

 of the individual it would succumb before the regeneration could 

 take place. 



These considerations make it clear, in my opinion, that the 

 lack of complete power to regenerate in amphiuma can not be 

 interpreted as having any connection with the unimportance of 

 the legs to the animal. It should not be overlooked that it is 

 not that the leg does not regenerate at all ; in fact it regenerates 

 quite well, but that the new part is different from the old. It is 

 at least conceivable that some simple physical or physiological 

 factor may interfere with the formation of the complete toes, 

 such, for instance, as the thickness of the skin in relation to the 

 size of the limb. 



