LIFE HISTORY OP LAKE HERRING OF LAKE HURON 



325 



measured belong. The average of the differences between the calculated lengths 

 of the two series is shown at or near the bottom in each table for each year of hfe. 

 These data show that the length computations based on the diameter are always 

 higher than those based on the anterior radius of a scale, and that the difference between 

 the computations of the two series increases consistently with each earlier year of 

 life for which calculations are made, so that the ma.ximum average difference of 13 

 millimeters is found in year I. 



Table 19. — Differences between calculated length values based on different scale dimensions, accord- 

 ing to number of years intervening between the age of the fish at death and age for which calculations 

 are made 



' Value in parentheses excludes the differences of years II and III. 



Table 20. — Amount of correction necessary to bring calculated length values, based on anterior radii, 

 into agreement with those based on diameters. Correction factors are based on values of Table 19 



When we arrange the differences between the computations according to the 

 time that intervenes between the age of the fish at death and the age for which the 

 length is computed (Table 19) we see that, except in young fish, the disagreement 

 between the values of the two series is insignificant when only one year intervenes 

 but becomes increasingly significant with each additional intervening year until the 

 maximum difference of 13 to 15 millimeters is reached for the first year of life. It 

 is to be noted in Table 19 that the values of each column steadily decrease from 

 top to bottom. This means that the difference increases more rapidly with each 

 additional intervening year in the young than in the old herring. The difference 



