MUTILATION AND REGENERATION 379 



arthropods regenerate their limbs when broken there. 

 Cockroaches regenerate the tarsi, but not the leg above 

 the tarsi. 



The regenerative power appears to be greater in pro- 

 portion to the youth of the animal. Embryos, larvae, and 

 young animals are much better able to regenerate lost 

 parts than are fully formed and old animals. The tad- 

 pole may regenerate a tail or a limb, but the frog very 

 rarely and imperfectly regenerates any lost member. 

 When legs are cut off of caterpillars, they are sometimes 

 regenerated during the pupa stage, so that the imago 

 has the full complement. 



Temperature has a marked effect upon the regenerative 

 function. Most of the animals possessed of regenerative 

 powers are " cold-blooded," when cold they are inactive; 

 when warm their metabolic functions accelerate, so 

 that if they are kept warm or the experiments performed 

 in the summer time, regeneration is accelerated. 



Lastly, complexity of structure has something to do 

 with the regenerative function. When one sees that 

 the power is highly developed among the lower verte- 

 brates and that complexly organized members, such as 

 salamanders' legs and eyes, can be correctly reproduced, 

 he hesitates to dwell upon this point. Why should the 

 lizard regenerate its tail and not its legs; why should the 

 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 



