56 the periodic growth of scales in gadid.e 



111. Statistical Section. 



This section of my paper is chiefly concerned with measurements of 

 the surface size, enumeration of the lines of growth and annual rings for 

 scales of the following : pollack, poor-cod, whiting, haddock, and cod. 



The area of the body from which scales were generally selected for 

 examination was the median region of the flanks, that is to say, slightly 

 posterior to the pectoral fin, and either slightly above or below the 

 lateral line. 



In the majority of cases I have given data in the tables for half 

 a dozen scales from the same fish, three of which were taken from the 

 right side, and the other three from the left side of the body. 



Scales from any part of the body show annual rings, though scattered 

 among the normally developed scales are some minute scales mentioned 

 by Klaatsch, to which I will later refer. Of the five species mentioned 

 above, that which shows annual rings in the scales least satisfactorily is 

 the whiting ; so much is this the case that at times their determination 

 becomes a matter of real difficulty, and it is only after a comparison of 

 the lines of growth in scales from a number of specimens that one 

 attains any degree of certainty in the matter. The other species 

 mentioned show annual rings remarkably clearly, much more so, indeed, 

 than is brought out in the photomicrographs. The coal-fish {Gadus 

 viretis) and the Norwegian whiting-pollack (Gadus Msmarkii) also show 

 annual rings very distinctly (see plates), and I only regret that want of 

 time prevents my giving statistics for these two species. In regard to 

 the cod, Gadus callarias, L., from photomicrographs which I have taken, 

 it appears that the system would also be applicable to this species ; but 

 not having a complete series of this fish, I have only given a few figures^ 

 and more exclusively confined my attention to Gadidre of the English 

 Channel. 



In passing, I may say that I approached the subject of the age of 

 fishes with an unbiassed mind, as I had little previous knowledge as 

 to the ideas of either practical or scientific men on this subject, and it 

 was only after I had compiled my own statistics on age-determination 

 that I compared my results with those arrived at by other workers by 

 different methods (see Cunningham, Fulton, etc.). 



The determination of the years of large and aged fish from their 

 scales is a much harder task than in the case of younger fish, as the 

 scales of the former have, firstly, become much thicker and less trans- 

 parent, and secondly, the scales of such are frequently more or less 

 disintegrated. As an illustration of this one may notice the photo- 

 micrograph of a scale of a pollack 31 inches in length, which appears 

 to possess 8 annual rings (see Plate IV.). 



