THE MEASUREMENT OF VARIATION. 



typhus fever cases to age; type d that of typhoid fever 

 cases to age, and also senile mortality statistics. Fi- 

 nally, type s represents various slight degrees of skew- 

 ness which are frequently found to occur even in anthro- 



a 



FIG. 6. Types of Skew curves. 



pometric and other series which had previously been 

 thought to be quite symmetrical. Most of the series 

 of deviation frequencies obtained by Warren * for vari- 

 ous crab measurements were found by him to be better 

 fitted by skew curves than by absolutely symmetrical 

 ones. 



Again, of the twelve series of measurements made by 

 Duncker f on the Flounder (Pleuronectes flesus), the six 

 which showed regular variations (number of rays in 

 dorsal, anal, and pectoral fins) were found to give very 



*Proc. Roy. Soc., Ix. p. 221. 



f Wissenschaf tliche Meeresuntersuchungen aus der biologischeu 

 Anstalt auf Helgoland, Bd. iii. p. 339, 1900. 



