234 Mr. E. Warren. 



nus and Carcinus as between two not very sharply marked off races 

 of a single species. 



Of course a considerable number of such comparisons would bo 

 necessary before any safe conclusions could be drawn, and the mean- 

 ing of the differences observed could only be discovered by such a 

 comparative treatment of a large series of genera. It is probable 

 that the larger deviations do indicate real differences in the correla- 

 tion constant, possibly such are associated with changes in habit or 

 environment. For example, it is conceivable that a crab which 

 swims might require to be more symmetrical than one that only 

 crawls between the tide-marks. Portunus does swim to a certain 

 extent, and one can see from the table that the correlation of the two 

 sides of the body is greater in this genus than in the essentially shore- 

 living Carcinus moenas. 



