380 BIOLOGY: GENERAL AND MEDICAL 



part usually reproduces the lost part, but sometimes re- 

 verses it. Sometimes a mistake is made and a wrong 

 part produced as when attempted regeneration of a 

 crab's eye terminates in an antenna-like structure 

 instead. 



Nothing of the amputated salamander's hand remains 

 to guide the growing tissues, yet a new hand complete in 

 all its parts is formed. It is as mysterious as the phe- 

 nomena of heredity yes, more so, for it seems more easy 

 to conceive that the ovum contains forces which by acting 

 and reacting upon one another may attain to a finished 

 product than that that product once finished shall be 

 able to restore itself when mutilated. The process of re- 

 generation, however, bears every evidence of being domi- 

 nated by hereditary influences, for that which grows 

 upon the amputated stump of the salamander is a sala- 

 mander's limb, not a lizard's tail or a mollusk's eye. 

 Spencer, Darwin, and all the writers upon heredity have 

 found it necessary to include the phenomena of regen- 

 eration among those for which heredity must account, 

 and see in it additional evidence that the particular 

 kind of physiological units to which they attribute the 

 hereditary influences must be disseminated throughout 

 the body. 



But another curious fact awaits consideration. If the 

 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 



