SCALE OBSERVATIONS OF THE SQUETEAGUE AND PIGFISH. 303 



On the whole, Masterman's paper constitutes one of the most valuable contribu- 

 tions to scale literature. He suggests numerous researches on the subject that are 

 needed and that might profitably be followed. 



Calderwood (1914) takes up some of Masterman's criticisms of the spawning-raark 

 doctrine. Referring to Masterman's theory that the mark is due to absorption incident 

 to spawning he pointed out that the attrition is noted on the lateral, seldom on the 

 anterior, margin. If Masterman's view is correct, the anterior margin ought to suffer 

 most. It will be observed, however, that Masterman had taken this into consideration 

 and suggested that this absorption of the lateral margin rather than the anterior margin 

 might be in anticipation of the decreased girth after spawning. Calderwood also cites 

 Milne's observation that the thickness of the scale is increased at the spawning mark 

 which according to the latter observer is due to a continued secretion of the scale sub- 

 stance while the size of the body remains constant. Calderwood finds difficulty in 

 seeing how absorption of scale substance and a deposition of more at one and the same 

 time could take place; yet this must be true if Milne's contention is correct. Calder- 

 wood rather regards the attrition of the scale as necessary for the thickening and 

 toughening of the skin, but fails to point out very clearly just how this is accomplished. 

 He ends his paper by expressing the belief that the absence of the spawning mark is 

 valid negative evidence. 



In the application of the scale reading no more important work has been pub- 

 lished than that of Hjort (1914). Since, however, no effort is made in this paper to 

 review the general applications of the subject which are entirely too voluminous to 

 permit it, further comment on his work may be omitted here. A great volume of 

 work of this nature has been done not only by Hjort and his assistants, Lea and Dahl, 

 but by McMurrich, Gilbert, Petersen, Johnston, Calderwood, Hutton, Esdaile, Masterman, 

 Hoek, and a host of others. 



The work of Winge (191 5) on the cod supplies much of the evidence that Masterman 

 found lacking in the salmon. He measured the "platelets" (Tims) or as he calls them 

 "sclerites," each one individually from the focus to the periphery, constructed curves 

 from these measurements, the maximal and minimal modes corresponding to the summer 

 and winter growths, respectivel}'. By comparing these scale measurements with the 

 actual lengths of living fishes measured, marked and recaptured, he was able to show 

 that these modes agree quite satisfactorily with the growth of the fish. These modes 

 (the summer and winter growth bands) are, in the cod, formed in September and March, 

 respectively. 



Another division of his paper deals with the question whether the growth of the 

 scale is exactly proportional to that of the fish. By measurements on four marked 

 cod, he finds a surprisingly close agreement — altogether within the limits of experi- 

 mental error. Furthermore, he was able to show that cod living under similar con- 

 ditions will show similar curves when plotted in his manner. And, finally, he tests 

 the otoliths as a means of determining age, using his data from scales as a check. Judg- 

 ing from his excellent technique, his results must be regarded as reliable. He concludes: 

 "* * * in the cod examined a very high degree of uniformity exists between the 

 growth of the scales and that of the otoliths. Both scales and otoliths exhibit growth 

 rings by means of which the age of the cod can be determined." 



