28 



C. M. JACKSON 



Body weight in grams 



over, the differences between the sexes in percentage weight 

 shown in the table are comparatively slight, usually well within 

 the limits of probable error. It is noteworthy that my data give 

 percentage weights which are slightly, but almost constantly, 

 higher than those of the curve derived from Hatai's formula 

 (fig. la). 



The heart shows a considerable degree of variability in abso- 

 lute weight (table 7), the coefficient increasing from 18 at birth 

 to 33.7 at twenty days and 29.7 at six weeks. At ten weeks 

 and five months the coefficient decreases (18.4 and 21.3) to near 

 that at birth. For the relative weight, however, the relations 

 are quite different. At birth and seven days, the coefficient of 

 •variation for the percentage weight of the heart is rather high 

 (15 to 18), though still somewhat less than that for the absolute 

 weight. From twenty days onward, however, there is remark- 

 ably little variation in the percentage weight of the heart, the 

 coefficient being usually less than 10. This corresponds to the 

 high coefficient of correlation between the weight of the heart 

 and the body weight after twenty days (0.840 to 0.968), which 



