VARIATION AND CORRELATION IN THE EARTHWORM. 201 



The point especially to be noted here is the great range of variation 

 and the rather high variability as measured by the standard deviation 

 and the coefficient of variation. 



The constants of the frequency distribution for variation in the length 

 of the earthworm are : 



It is seen from this that the earthworm is markedly more variable 

 in length than in number of the somites in the body, as measured by the 

 coefficient of variation in both cases. A portion of this difference is 

 undoubtedly due to the fact that length is a character very difficult to 

 measure accurately in the case of the earthworm. 



The constants for the variation in the number of somites from the an- 

 terior of the worm back to the anterior end of the clitellum, are given 

 in the following table : 



The marked!}' lower variability in this character (1.41 per cent.) as 

 compared with the total number of somites and the length, is note- 

 worthy. 



The number of somites in the clitellum was found to vary between 

 six and eight. The constants of the frequency distribution are 



It is of interest to note that the clitellum is decidedly more variable 

 with respect to the number of its somites than is the body in front of the 

 clitellum. 



The correlation between the number of somites in front of the clitellum 

 and the number in the clitellum was studied. The value of the coeffi- 

 cient of correlation in this case was 

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