LIFE HISTORY OF LAKE HERRING OF LAKE HURON 



311 



Table 8. — Length, in millimeters, reached by a lake herring 255 millimHern long at end nf each year of 

 its life, as calculated from difjerenl dimensions of scales taken from, the same and from various areas 

 of the body. The average is given for each of three series of scales for each year, as irell as limits 

 of variations represented by the minimum and maximum lengths shown in parentheses 



The calculated lengths also vary with the scales, as indicated by the limits of 

 variation shown in parentheses in Table 8. The variabiUty is much less (as is to be 

 expected) for the uniform scales of series A than for the scales of seiies B taken from 

 various places on the body. 



The above data show that neither the scales of a lake herring nor the parts of 

 one of its scales grow at the same rate, and that growth varies least for scales taken 

 from the same area on the body. To minimize the error in calculations due to the 

 differential growth of scales, I have selected for study that area whose scales varied 

 least in shape and size; namely, the one situated between the dorsal fin and the lateral 

 line. (See p. 274.) 



The question now arises : How close is the correspondence between the growth of 

 the selected scales and the body, and which scale dimension must be employed? 

 Previous workers almost invariably have selected the anteiior radius of the scale. 

 Their calculated values, when compared with the actual measurements, usually 

 were found to be too low. As the scale hypothesis really assumes a correlation between 

 the increase in the length of the body and the length, not radius, of the scale, it might 

 be possible to eHminate the discrepancy between the calculated and actual values 

 by the employment of diameters instead of anterior radii. The length averages com- 

 puted from scales of series C, Tal>le 8, and based on anterior radii and diameters, 

 indicate at least that the calculated values are increased considerably by the employ- 

 ment of scale diameters. Also, the variabihty of the calculated lengths based on the 

 diameter is much less than that of the lengths based on the anterior radii, at least in 

 the specimen considered. 



Therefore, I have undertaken a series of measurements of small and large lake 



herrings to ascertain the degree of correlation in growth of body and of the selected 



scales and to detemiine whether the diameter of a scale is a better dimension than 



the anterior radius from which to calculate length values. In my paper (Van Oosten, 



99760—29 4 



