48 



It has been stated that it is necessary that a walking-leg be 

 held in order that autotomy may be effected . This points to the 

 probability that in the lobster and its allies evasion of an enemy 

 is the most potent factor in the production of autotomy. This 

 is borne out by the fact that lobsters when kept together in cap- 

 tivity are almost invariably found short of one or more legs after 

 some time, because of the constant fighting. In those taken from 

 the sea, where encounters cannot be so frequent, the loss is, as 

 before-mentioned, comparatively small. 



In the Brachyura escape or damage in fighting is not the chief 

 end of autotomy, for fifty or more will live in one tank for many 

 days without a single limb being cast off. This is at first puzzhng 

 when the following tables are examined : — 



Shore Crabs collected at Cullercoats, Northumberland, 

 January, 1915, from Rocky Shore. 



Shore Crabs collected from Rocky Shore at Keppel, 

 Millport, March, 1913. 



From the above it is seen that in medium-sized and large 

 crabs about 50 per cent, have lost one or more legs. The explana- 

 tion of this great loss almost certainly hes in the fact that on the 

 shores where these animals live there is, in winter, a constant 



