REGENERATION 1 1 7 



that tlie limbs of li/.ards are not replaced is. I believe, due to 

 the fact that these animals are seldom seized by the leg, owing 

 to their extremely rapid movements. But if a lizard does hap- 

 pen to be caught by one of its limbs, it must fall a prey to its 

 pursuer, and the capacity for regenerating the limb would be 

 useless. The case is very different with regard to such animals 

 as Tritons. Their movements are much less rapid, and their 

 assailants, being too small to swallow the whole animal, fre- 

 quently bite off a limb. They are often attacked by members 

 of the same species, which gnaw off a gill, limb, or the tail of a 

 weaker comrade, bit by bit. If a considerable power of regen- 

 eration were possible at all, it would certainly be provided in this 

 case. This power is possessed in a much smaller degree by 

 Proteus ; but these animals are only found in the caves of Car- 

 niola, where enemies larger than themselves do not exist, and 

 in which there is no great competition for food, and therefore, 

 at least as far as my observations extend, they do not bite one 

 another. 



Spallanzani has stated that nature does not reproduce every part 

 that is cut off; expressed in theoretical terms, this simply means 

 that the various organs of an animal possess the power of regener- 

 ation in diff'erent degrees. If we inquire further into the question, 

 we shall tind that those parts which are most frequently exposed to 

 injury or loss must possess the power of regeneration in the high- 

 est degree. So far as I can judge from the facts with which we 

 are at present acquainted, this remark appears to me to be a per- 

 fectly correct one. Unfortunately Spallanzani gives no instance 

 in support of the above statement, so that we do not know what 

 parts he referred to. I have myself, however, made some investi- 

 gations in order to ascertain whether the degree of regeneration 

 of a part bears any relation to its liability to injury. 



If regeneration is a phenomenon of adaptation, the internal 

 organs — which are not exposed to injury in the natural life of 

 the animal — cannot possess any regenerative power, even in 

 those animals in which the external parts — which are exposed 

 to the attacks of enemies — possess it in a high degree. 



The following experiment bears upon this point : — I cut open 

 a large newt {Triton cristatus). removed about half of the right 

 luns:, and sewed the skin together again. The animal soon 

 recovered from the effects of the chloroform, and its wounds 

 healed : it was then well cared for for fourteen months, and 



