— H - 



principal values are: (Fig. i). i) The maxijnum of the curve, or the mode (D.) i.e., 

 those length- classes of the plaice to which the greatest number of individuals be- 

 long, 2) the arithmetic average (A.) or medium length of all the plaice represented 

 by a curve, 3) the median (C.) or central value; that length- value above and below 

 which lie the half of all the plaice (in single values) and the ordinate of which divides 



% 



A. S. 

 9 0% 

 Ô W% 

 y 33% 



6 307„ 



5 25'/, 



/J 20% 



3 15% 



2 10% 



1 5% 



Fig. 2. Analysis by lengths of 34,209 plaice from Area Bs, measured in English ports in June of the three 



years 1906 — 1908. A, ordinary curve with the numbers for each single centimetre; B. smoothed curve with 



the numbers for each 5 centimetres; C. summation or integral curve. Percentage curves. 



the whole area of the curve into two equal sections. Other important principal values 

 are the two Quartiles (Qu) which lie above and below the median, at a distance of 

 25 7o of the whole series from this, and between the ordinates of which one half of 

 the whole area of the curve is enclosed; also the two Deciles (Dc.) lying each 40%, 

 and the two vigintiles, lying each 45 % respectively from the median. 



The graphical representation of a series of measurements of a plaice sample can also 



