LIFE HISTORY OF L-^KE HERRING OF LAKE HURON 339 



of an age group appears to give corrected computed lengths, which are at least 

 approximately accurate. 



As stated on page 317, scale formation in the lake herring very probably begins at 

 a body length of approxunately 35 to 40 millimeters. Assuming 35 millimeters to be 



correct, the cdVrective formula, then, is Li = 35+ -^ (L-35), etc. Both uncorrected 



and corrected computed lengths are shown in Table 24. Identical fish were employed 

 for both series. The uncorrected computed average lengths are shown in the left 

 half of the table; the corrected computed lengths in the right half. If we compare 

 the corresponding values of each age group of Table 24 we find that three principal 

 changes occur when the computed lengths are corrected by Lee's formida. First, 

 the averages are raised in an amount that decreases gradually from the early to the 

 late years of life. Thus, the averages of the 4-year fish of the 1918 year class (Table 

 24) when corrected are raised 17, 8, and 3 millimeters m years I to III, respectively. 

 Second, the increments are decreased in all years except the first. Thus, the incre- 

 ments of the 4-year fish of the 1918 year class (derived from Table 24) for years 

 I to IV are, when the computed lengths are uncorrected, 116, 62, 34, and 18 milli- 

 meters, respectively, but when the computed lengths are corrected they are 133, 53, 

 29, and 15 millimeters, respectively. Third, the "phenomenon" is less pronounced 

 so that the lengths of the different age groups of the same year class become more 

 comparable. This is seen in the computed lengths of the 1919 year class (Table 24). 

 The lengths computed for the first year of life for the sixth, fifth, fourth, and third 

 age groups are, when uncorrected, 116, 118, 121, and 128 millimeters, respectively, a 

 difference of 12 millimeters between the extremes, and 136, 136, 138, and 143 milli- 

 meters, respectively, when corrected, a difference of 7 milluneters between the 

 extremes. Similarly, for the lengths of the second and third years of life the differ- 

 ence between the extremes is reduced from 25 to 17 millimeters and from 26 to 17 

 millimeters, respectively. 



A study of the computed lengths of Table 24 shows that though Lee's "phenom- 

 enon" becomes less pronounced when the lengths are corrected by her formula, the 

 "phenomenon" is still strikingly evident in the corrected calculated lengths. 



Table 24 shows further that for the third and later years of life the corrected 

 computed lengths of a year class agree more nearly with the actual measured lengths 

 for corresponding years than do the uncorrected computed lengths. Thus, computa- 

 tions show that in the year class 1919 the average deviation of the calculated lengths 

 from the actual for year III is 16 millimeters for the uncorrected values and 10 milli- 

 meters for the corrected (Table 24). Sunilar results may be obtained for the later 

 years of life. Whether the corrected values for years I and II likewise coincide more 

 nearly with the measured than do the uncorrected can not be definitely determined 

 at the present time owing to the lack of 1 and 2 year fish in my samples. If, how- 

 ever, the 34 Sagmaw Bay herring of j^ear II, with an average length of 202 milluneters 

 (Table 14), be taken as a standard, then we may state that for year II the corrected 

 values are the more accurate. Attention may be called again to the fact that the 

 actual measured lengths of the younger age groups may be too high (see p. 334) and 

 that the uncorrected values, therefore, may, in reality, be more accurate than the 

 corrected values. 



