MUTILATION AND REGENERATION 397 



lost part be replaced by a similar part removed from 

 another creature of the same kind, the regenerative 

 function is inhibited. The new part is accepted in 

 lieu of the old one, grows fast by the process of healing, 

 and a short cut to the desired end, the restoration of 

 symmetry, is accomplished. By virtue of what impres- 

 sion is the suspension of regeneration brought about in 

 such cases? How can the creature or any of its parts 

 know that it need not grow a new limb because some 

 accident has already furnished one? Why is it satisfied 

 with one ready made instead of making the new one 

 itself? These are problems difficult of solution, the 

 answers to which may never be known. The matter 

 becomes still more difficult if the adaptation theory be 

 entertained, for, granting that regeneration be an 

 adaptation, the failure of regeneration in those cases 

 where the new limb is substituted for the amputated 

 one never can be so regarded, seeing that the imagina- 

 tion can scarcely entertain such a thought as that of mu- 

 tilated animals finding adapted parts with which to 

 replace those lost and so doing away with the necessity 

 of preparing them. 



Though the regenerative phenomena extend through- 

 out the different phyla of animals, examples being found 

 among such vertebrates as fishes, batrachians, reptiles, 

 and birds, it does not extend to the mammals. No 

 authenticated cases are on record in which parts lost by 

 mammals have ever been regenerated. These highest 

 and most complex of living organisms are unhappy in 

 being without so useful a function. Among them 

 all that can be hoped for is that healing may follow 

 injury. 



III. The Mutilated Organism Repairs Itself Without 

 Restoring its Symmetry. This method of repair has 

 several times been referred to as "simple healing." 

 It takes place through proliferative activities of the 

 simpler epithelial and connective tissues. It also 

 includes restoration of a few damaged tissues, so as to 

 be regenerative in tendency. 



