Variation in Portunus depurator. 



233 



inclined at tan l r to the axis of x. The ends of the lines are irre- 

 gular on account of the impossibility of obtaining a satisfactory mean 

 to the relative at these points because of the paucity of individuals 

 near the limits of the range of deviation. One sees that, in these two 

 cases at least, the correlation surfaces must closely approximate to the 

 symmetrical normal surface. 



In the above table the 2nd and 4th columns give the values of 

 Galton's functions which Professor Weldon found for two races of 

 female Carcinus moenas ('Roy. Soc. Proc.,' vol. 54). The sixth 

 column gives the values of r obtained for Portunus. 



It is quite obvious that there is a marked similarity between the 

 three columns of figures. The probable errors of r were found by 



1 r* 



the formula G'6745 =. which Professor Pearson shows will 



yXl+r 2 ) 



give a close approximation (' Phil. Trans.,' vol. 187). These probable 

 errors were added to indicate how far the differences in the values of 

 r are to be regarded as meaning actual deviations in the constants. 

 The values obtained for the two races of Carcinus differ from one 

 another nearly as much as they do from the constants of Portunus. 



"We have thus proved that the mutual relationships of the organs 

 measured are almost as closely similar between the two genera Portu- 



