396 BIOLOGY: GENERAL AND MEDICAL 



salamander regenerate its tail, legs, and eyes, but not its 

 head; why should certain birds be able to regenerate 

 the upper mandible, but not the limbs? These are diffi- 

 cult questions that cannot be correctly answered in the 

 present state of knowledge. An attempt has been made 

 to regard the regenerative function as a matter of adapta- 

 tion by which those organisms most apt to be mutilated 

 have become equipped for the emergency by an unusual 

 activity of the reparative function. In support of this 

 theory, the breaking-joint of the arthropod leg is urged as 

 a cogent argument. 



Much interest attaches to the nature of the influences 

 governing the reparative process. The newly formed 

 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 



