AS AN INDEX OF AGE. 59 



Pollack lf-2f inches in length, caught on 8th July, would thus be 

 about three months old, and these show, on an average, 3-4 lines of 

 growth, thus giving a formation of 3-4 lines in two months. 



Cunningham further says, " In October I have taken a number in 

 Cawsand Bay, 3|-4f inches long, and I have no doubt these were 

 hatched in the preceding spring." 



I have examined Cunningham's actual specimens, and the scales of 

 these give on an average 15 lines of growth, and tlieir structure bears 

 out his statement, and gives a formation of approximately 2-3 lines 

 of growth per month. 



Two months later, in December, there are an average 18 lines of 

 growth, giving an addition of 1-2 lines of growth per month. One 

 would naturally expect to find fewer lines of growth during these winter 

 months. In another sentence Cunningham says, " The pollack caught 

 in Plymouth Sound in June and July are 12-15 inches long, and are 

 probably in their third year." 



This is also brought out in my table. It will be seen there that a fish 

 15 inches long captured in the middle of June has 2 annual rings and 

 7 young lines of growth occurring on its scales. 



If growth for the third year started in the middle of April, this again 

 would give a formation of about 3 lines per month. 



In the following detailed tables dealing with the pollack, I have given 

 a comparison of scales from four different regions of the body in two 

 cases, firstly, that of a young fish (3-79 inches), and secondly, that of 

 an older fish (1519 inches). The four regions of the body from which 

 scales were examined in these two cases were the following : — 



(1) The anterior region, laterally, slightly posterior to the eye. 



(2) The median region of the flanks, that part of the body which 



has the greatest depth vertically beneath the first dorsal fin 

 and posterior to the pectoral fin. This has been the usual area 

 from which I have examined scales throughout my investiga- 

 tions. 



(3) Ptegion vertically beneath the posterior part of the second dorsal 



fin, adjoining the lateral line. 



(4) Ptegion vertically beneath the third dorsal fin, adjoining the 



lateral line. 



In a comparison of scales from these four regions the following facts 

 may be noticed : — 



(1) That commencing with the anterior area and proceeding back- 



wards to the posterior area, the number of lines of growth 

 increases in both the young and older fish. 



(2) That proceeding in the same direction, the length of tlie scale 



increases in a similar manner. 



