An Introduction to a Biology 



tether them to, so long as we realise that there is 

 no essential difference between, for instance, the 

 claws of the shore-crab and the forceps of the ana- 

 tomist ; and that such difference as there is lies in the 

 fact that the latter can be detached when no longer 

 required and attached when wanted again, while 

 the former is a useful tool only so long as it remains 

 part of the body of the crab. 



Mere detachability, however, is not the essential 

 feature of the human implement, because it happens 

 that in the case we have chosen from the other 

 animals the implement can be detached. If the 

 claw of a crab is badly injured it can be voluntarily 

 cast off by the crab, by a deliberate transverse 

 fracture of the limb near the point where it is at- 

 tached to the body, but not, curiously enough, at 

 a functional joint. A new limb is then grown in 

 the place of the discarded one. It is an interesting 

 but not a surprising fact that a crab has to be in 

 very good health to be able to perform the operation 

 of amputating its own arm in this way. This 

 amputation may also be performed by a crab when 

 its limb is securely held by an adversary. 



The essential difference between man and the 

 other animals cannot, therefore, be expressed in the 

 simple statement that man is distinguished from 

 other animals by the fact that he is a tool-using 

 animal. Limb and tool are two names for the same 

 thing. Nor does the difference lie in the fact that 

 this thing, whether we call it limb or tool, is detach- 

 able in man and not detachable in other animals. 

 For we have just seen that it is detachable in the 

 crab. The difference lies in the fact that man can 



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