122 THE BIOLOGY OF THE SEA-SHORE 



the following figures relative to the loss of limbs in shore 

 crabs taken from their natural habitat : — 



Shore Crabs collected at Cullbrcoats, Northumberland, January, 

 1915, from Rocky Shore 



Shore Crabs collected from Rocky Shore at Keppel, Millport, 

 March, 1913 



From these tables it is seen that of crabs three years old 

 and upwards collected from rocky shores, 50 per cent, are 

 found to have lost a limb. On the other hand, among crabs 

 collected from sandy beaches at the same time of year, the 

 percentage is said to be ver)' considerably lower. Paul con- 

 cludes, in consequence, that the chief factor in producing 

 autotomy is crushing by the movement of stones, and this 

 would be most pronounced after ^^^nter storms. Fighting 

 is not the cause, since as many as fifty crabs of various sizes 

 live peaceably in one tank, and only one autotomised limb 

 may be found in weeks. The purpose of self-amputation, 

 as has already been mentioned, would be the prevention of 

 haemorrhage rather than escape, since it allows the valvular 

 mechanism at the breaking plane to close. In lobsters and 

 prawTis, on the other hand, the object of autotomy is thought 

 to be escape. 



Against Paul's adaptive and purposive interpretation of 



