Correlation and Fan at/ on m the Toad 60 1 



that we have here a form quite unique among vertebrates hitherto 

 reported, in both the extent and uniformity of the difference in 

 variabihty of the sexes. The matter will be discussed in connec- 

 tion with the subject of correlation. 



b The Frequency Polygons 



We have noted that distributions of all the characters in both 

 sexes are skew and that the skewness in nearly all cases is negative, 

 being positive only in the liver and gastrocnemii of male. The 

 negative skewness, which means merely that the majority of indivi- 

 duals are below the modal value of a type, was to have been 

 expected because of the inclusion of individuals of all ages of one 

 year or more. It is probably merely an indication that the younger 

 outnumber the older in our material, at any rate we need look no 

 farther than this for a sufficient explanation of the skewness. It is 

 indeed surprising that the skewness is so slight indicating that in 

 this general population survival to middle or old age is usual. 

 The positive skewness of the livers is an expression of the fact that 

 in these as in most vertebrates the liver is relatively larger in the 

 younger animals. 



c Comparative Variability of External and Internal Characters 



There have been remarkably few exact studies of the vari- 

 ability of internal (visceral, etc.) characters and as far as I have yet 

 been able to discover these have been observed only in man with 

 but a single exception. Greenwood ('04) has given the coefficients 

 of variability for the heart, liver, spleen and kidney in a hospital 

 population of males. Pearson ('97) has calculated the coefficients 

 for the heart, liver, kidney and brain from the data published by 

 Clendinning, Reid and Peacock, and Sims published in 1838, 1843, 

 1846, 1854: probably these data have not the accuracy required 

 by present statistical methods, indeed it is known that in securing 

 them many were rejected on account of their supposed "abnor- 

 mality." The coefficients of these human viscera vary between 

 38.2 and 14.3. The brain of course has furnished a more complete 

 series of data. These have recently been collected and summa- 



