Variation in Portunus depurator. 231 



where n = number of individuals, and <T A and <T B are the standard 

 deviations of organs A and B respectively. This formula has recently- 

 been shown by Professor Pearson to be superior to the one formerly 

 used (' Phil. Trans.,' vol. 187). 



The correlation surfaces are published as being of permanent value, 

 and it is believed that such material as this will be of use in the 

 future in elaborating or modifying the current theory of correlation. 



Figs. 5 and 6 represent two r lines. The crosses were obtained by 



FIG. 5. E. and L. Antero-lateral. r = 0'86. 



I 



Dotted line = the r line inclined to axis x at tan" 1 0'86. The continuous line 

 joining the crosses is the line found on taking E. antero-lat. as subject. The 

 circles indicate the points obtained when the L. antero-lat. is the subject. The 

 probable errors of the dimensions are represented by the intervals 1, 2, 3, &c., 

 on both horizontal and vertical scales. 



