16 



Then B. mentions the peculiar 

 conceatric rings or zones in the scales 

 oi the eel — what I have above 

 called the annual rings. His words 

 are as follows: 



»The piates are not only arran- 

 ged in longitudinal rows; they show 

 also another grouping which I consi- 

 der worthy of attention. In place 

 of being distributed in the same way 

 over the whole surface of the scale, 

 they usiialiy form various concentric 

 zones, which are mutually separated 

 more or less distiuetly by an inter- 

 .space, which is occupied by the 

 fibrons substratum of the scale. There 

 are in general 3 to 4 of these con- 

 centric rings OU a scale of 2 to 3 

 mm. in lenglh. — When the central 

 zone is well isolated, it gives oue the 

 impressiou of being a small scale 

 brought into the ceutre of a larger 

 scale. These perhaps represent zoues 

 of growth. However this may be, 

 the calcareous piates found along the 

 outer margin of each zone usually 

 give oue the impressiou of being 

 quite rudimentar}^; they are smaller, 

 very narrow, sometimes indeed redu- 

 ced to a level and straight comb. 

 The piates in the central zone are 

 in general smaller thau those found 

 in the zoues further out towards the 

 periphery of the scale. In the median 

 part of the central zone there is 

 usually a larger or smaller empty 

 space consisting of the scale's fibi'ous 

 ground-substauce, which is overstrewu 

 with single or in various ways aggre- 

 gated, calcareous graius. 



»The membranous plate which 

 forms the substratum of the calcar- 

 eous piates is formed of conuective tissue, the fibres of which are arranged more 

 or less parallel to the margin of the scale. To be able to see these fibres exactly 

 the inuer surface of the scale must be examiued under a liigh power. Treated 

 with a concentrated solution of warm potash, the connected tissue is dissolved and 



Chr. D. Lunn ad naturam del. x 70. 



Fig. 1. Scale of a female eel talten in the Sound, Decemlior 1906. 



The scale ghows 6 annual rings (central zone-}- 4 concentric zones) 



and wns thus hiid down in the summer of 1902; the eel conse- 



quently had arrived in the spring oC 1900 as glass-eel and was 



tlius 7 years old, counling from the date of immigration (more 



exactly, 6 years and 7 months) 



It is very clearly seen tbat llie annual ring for 1906 is 



completely formed. 



