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Are the concentric zoues (rings) in the scale of tlie eel tb be considered 



as annual rings? 



The idea that periodicity in the growth of a fish should be so impressed 

 OU tlie structure of the scales, that we might be able at once to read on them 

 how many periods or in other words: how many years the specimen examined 

 has lived — is not new. That this method has beeu used for the determination 

 of the age of tlie carp is well-known (see the papers by HofEbauer: Die Alters- 

 bestimmung des Karpfen au seiuer Schuppe. Jahresbericht des Schlesischeu 

 Fischerei-Vereius 1899; and Weitere Beitritge zur Bestimmung des Alters und 

 Wachstumsverlaufes an der Struktur der Fischschuppe. Jahresbericht der teich- 

 wirthschaftlichen Versuch-Station zu Tracheuberg. 1901). — It has also been used 

 however for age-determiuation on other fishes, for example, herring and gadoids. 

 J. Stuart Thomson has published a paper: The periodic growth of Scales in Gadidæ 

 as an Index of Age (in Vol. VII, No. 1 of the Journal of the Marine Biological 

 Association of the United Kingdom, Plymouth 1904), in which he shows the annual 

 rings in the scales of several gadoids and comes to the following result with regard to 

 the practicability of the method: »After an iuvestigation of thousands of scales from 

 these gadoids, I hold that in 98 cases out of 100 oue would arrive at a very 

 closely approximate idea of the age of the fish from an examination of 3 or 4 

 well-developed scales taken from the median region of the flanks near the lateral 

 hne.« This sentence may also be extended to include the scales of even the cod 

 (Gadus callarias L.J, and presumably this is also Stuart Thomsou's meauiug, 

 though he has ouly examined a few of them. More detailed iuvestigations on 

 this matter were however undertaken by the Dåne, Chr. D. Lunu, during a stay 

 at the Bergen Museum in 1905; as these are not yet published and I have had the 

 opportunity through the kindness of the author to ascertaiu the results, I shall 

 only mention that L. has fouud the annual rings very distinct and well-developed 

 on the scales of the cod from Norwegian waters. They are less distinct on the 

 scales of the cod from our own waters. — It would lead too far afield to enter 

 here upon a detailed account of the scales of the cod. So much only may be 

 said, that the numerous small piates (scalelets) iuto which the surface is divided 

 are arrauged in radial rows and have a very variable lumen; this causes the 

 appearance of concentric rings, as in the radial rows many small piates with 

 broad lumina alternate with a few in which the lumina are much narrower. The 

 iuvestigations mentioned have now shown that the wide and broad, small piates 

 are formed in summer, are summer-rings, and that the contracted and narrower 

 are formed in autumn (and winter), are wiuter-rings, so that the annual ring 

 consists of many small piates with wide lumina and few with narrow; as the 

 latter are formed last, the boundary between two annual rings is seen very 

 distinctly. 



This condition will remind the reader of the concentric zoues in the scales 

 of the eel, as mentioned in describing the latter; in these also there is a difference 

 in each zone between broad smali-plates in the luner, first-formed part and uarrower 

 small-plates out towards the margiu. — That the zones in the scale of the eel are 

 even more distinctly marked off, in that the ground-substance of the scale is 



