334 



J. ARTHUR HARRIS 



that between the total length of the organism and the relative length of 

 either anterior or posterior element. 



JENNINGS (1911, p. 63) has emphasized the high variability of the 

 post-oral dimension. Table 3, in which all the coefficients of variation 



TABLE 3 



Coefficients of variation for anterior and posterior fractions of length 



in Paramccium. 



are laid side by side, fully confirms his conclusion in this regard. Utiliz 

 ing these coefficients of variation we obtain the values for the correlation 

 between total length and the deviation of the anterior length from its 

 probable value, given in the fourth column of table 2. 



These constants are negative in sign throughout, and while variable 

 in magnitude all may reasonably be considered statistically significant 

 in comparison with their probable errors. 



Thus when Paramecium varies in length both anterior and posterior 

 fractions of the body contribute to this variation, but as length in 

 creases the anterior portion becomes relatively shorter. 



For one series, the unseparated conjugants of race k. I have deter 

 mined the regression of the anterior length on total length and the re 

 gression of the deviation of the anterior length from its probable value 

 on the total length of the organism. The equations are 



a == 3-0359 + -4977 I 

 ^==.7616, s a = 3.3743 --.1135 / 



The equations and empirical means are represented graphically in 

 diagrams i and 2. In both cases the relationships are sensibly linear. 



