MUTILATION AND BEGENERATION 395 



regenerate many times in succession, if the amputation 

 be performed too close to the body, healing without 

 regeneration results. The legs of crabs and lobsters 

 regenerate best from a certain point known as the 

 " breaking-joint," where the legs are constricted and 

 weakened so that when the animal is caught and held it 

 not infrequently frees itself by fracturing the leg at this 

 point. If the leg be broken below the breaking- joint, 

 the animal usually rebreaks it at that point and casts 

 aside the intervening piece. When the leg is amputated 

 above the breaking-joint, it is regenerated with greater 

 difficulty. Centipedes, tarantulas, and walking-stick 

 insects are found to have "breaking-joints," and these 

 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 



