312 



BULLETIN OF THE BUREAU OF FISHERIES 



1923) on the New York Aquarium whitefish I stated that for a study of the corre- 

 spondence in growth of body and scales it is essential to acquire a large amount of 

 homogeneous material collected at the same time and place, and that in order to check 

 the calculated values series of fish of the same year class collected in the same season 

 of different years and in the same locaUty must be employed. No such whitefish 

 material was at hand at the time of writing, though the material available did lead 

 to certain conclusions. At present much more desirable material is available in the 

 collections of lake herring made at Bay City, Mich., on October 26, 27, and 29, 1921, 

 November 3 and 4, 1921, November 1, 1922, and November 12, 1923. As explained 

 ill detail on page 280, the collections of October 29, 1921, November 1, 1922, and 

 November 12, 1923, are presumably homogeneous in character, as each was taken 

 from one pound net and consisted of fish ready to spawn. 



AGE VARIATIONS IN THE GROWTH OF THE HEAD 



As variations in the body-scale ratios of the different age groups may be due to 

 age variations in the growth of the head, I measured, in addition to the diameter 

 (F) of a scale and the body length (E) measured snout to caudal, the length of the 

 scale-covered portion of the body, excluding the head and tail. The last measure- 

 ment (T or Ti) was obtained by subtracting the length of the head {H or Hj) from 

 the body length (K).^" From these measurements I computed the following ratios: 

 11/ K, HJK, HJV, K/V, and Ti/F. The H/E ratios were determined for lake herring 

 collected in 1917 and 1919 at various localities on Lake Huron. The Hi/E, Hi/V, 

 E/V, and Ti/F fractions were computed for 191 herring taken at Bay City, Mich., 

 October 26 and 27, 1921. i7,/Fis the difference between E/ V and Tj/V. A summary 

 of the data is given in Table 9. 



Table 9. — Average for each year of H/K ratios for 177 lake herring collected in 1917 and 1919 at 

 various localities on Lake Huron, and average of HijK, K/V, and Ti/V ratios for 191 lake herring 

 collected at Bay City, Mich., October 26 and 27, 1921, to indicate age variations in growth of the 

 head. X and non-X scales were employed in the fractions K/V and TijV. The H\IV ratio is 

 the difference between K/V and TiJV ' 



1 Numbers in parentheses indicate the numbers of specimens employed. 



The EjE ratios of the 1917 and 1919 herring remain practically constant 

 with the j^ear classes and with age, the difference between the extreme averages 

 being only 0.004. The head of the 3-year fish is the smallest. The EJE ratios 

 of the Bay City herring also remain constant with age, the difference between the 

 extreme averages being 0.004. In these fish the head of the 3-year-old is the 



11 For details relative to the methods employed in obtaining K, T, H, Hi, and Ksee p. 274. 



