SCALE OBSERVATIONS OF THE SQUETEAGUE AND PIGFISH. 3OI 



of the several bands. By this means he shows that comparisons of fish of different 

 localities can be made with much fewer fish. Suspecting that the scale-covered parts 

 and the remaining parts of the body of the fish might not grow in the same proportion 

 he made measurements to show that errors from such a source would be negligible. 



Hutton (1909, 1910, 1914b, 1914c) wrote several papers popularizing and urging the 

 economic importance of fish-scale examination. He also gave some notes on photo- 

 graphing scales. 



Esdaile (191 2) did a valuable work in determining the degree of variation of scales 

 on different parts of the salmon, Salmo salar. She shows that within certain limits 

 the circuli in each year band ("peronidium") is proportionate to the width of the scale, 

 but different in absolute number on different parts of the body of the fish. Criticism 

 of this part of her work is offered below in connection with the writer's observations on 

 age determinations (q. v.). In her second paper (1913) Miss Esdaile gives the results 

 of investigations of salmon scales devoted largely to points in the life historv of that 

 fish. 



Gilbert (191 3) worked on the salmon of the Pacific coast after essentially the 

 same methods as those employed by Dahl, Hutton, Thomson, and others. His scale 

 photography is brought to a high degree of perfection, and deserves special mention. 



Milne (191 3) in a work similar to Gilbert's, on salmon of the Pacific coast, offers a 

 pertinent criticism of Dahl's (and Johnston's) method of calculating length. He was 

 able to test this method by scales of two fishes captured, marked, measured, and 

 recaptured by Johnston. On one, Milne points out, Johnston's calculation showed an 

 error of only one-half inch for the kelt measurement of a 27-inch salmon; the other 

 showed an error of 6 inches for a 26j4'-inch fish, from which he concludes "either that 

 the scale is abnormal, or that Dahl's system of measurement is not applicable to a fish 

 that has spawned." 



McMurrich (191 2), in addition to the methods of Gilbert and Milne, made use of 

 evidences found on otoliths. In these structures, zones or lines may be observed which 

 are believed by McMurrich and others to represent growth periods. 



Masterman (1913a) perceived that much of the work of recent investigators was 

 based on assumptions rather than on definitely settled facts. He therefore undertook 

 a careful critique of the work done on salmon, making an effort to decide whether it 

 had been proved that summer and winter growth rings are invariably and indubitably 

 formed in their respective seasons; and whether the spawning mark invariably records 

 the spawning period; and whether its absence can be taken as denoting maiden fish. 



He states the usual assumptions of age determinations, but is doubtful of the 

 reliability of this method beyond the fourth or fifth year of growth. Concerning the 

 manner of growth of the circuli, he says: "They have an innate tendency to be produced 

 roughly in lines equidistant from the center and at a certain distance from the preceding 

 ridge * * * The distance between neighboring ridges is determined by the rate 

 of growth at the time." In addition to the accumulation of circuli in summer and 

 winter bands, he notices other morphological arrangements of the circuH which may 

 also help to indicate the seasons of active growth; but, to quote him on this point, 

 "In the case of sea fish, at any rate, they may just as likely have reference to changes 

 in food and temperature, with no direct reference to the calendar." 

 97867°— vol 34—16 20 



