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process of forming« before the first half of June; araong a number of eels taken at 

 Struer ou June 18th there was a single speeimen vith the scales just forming; it 

 measured 18 cm.; the central zone was still far from being completely formed, as 

 only a few rows of small piates were completed. As other investigations and work 

 claimed the time between the Ist of July and middle of August, we only once 

 had the opportunity of obtaining small eels; but just at that time on July Uth 

 I found an eel of ISy, cm. long in Faxe river in which the scales must have 

 been laid dowu about that time; so few small piates namely were present that they 

 did not form even a continuous row; nothing else was seeu of the scale. 



When the investigations were again taken up in August, it was found 

 that scale formation was far advaneed; this will be seen from the earlier used 

 Table 3; all the spedmens marked 1 have assumed their scales in the summer of 

 1906, so that only a central zone was present. The explanation to the Table 

 already given shows that the grovvth of the central zone had already ceased in 

 some. And the growth of the new as of the older scales is always ended towards 

 the end of September. 



This ought to be sufficient proof that a zone, either the central zone itself 

 or a conceutric zone, is formed in the scales of tlie eel in the course of a growth- 

 period exteudiug over some months. I use the term annual ring for these as it 

 seems to me more practical than »summer-ring«, though the latter is really the 

 more correct. 



With the aid of these two raethods: the raeasurement-method, which is 

 used firstly on the eels under the scalelimit, and the method of investigating the 

 scales, the work has been carried on to determine the growth of the eel and to 

 determine how long they remain in our waters before they are again on the way 

 back to where they came from as tiny fry. 



We may now examine more closely the whole growth-period of the eel, 

 following it from the moment when it appears as elver on our coasts until it again 

 leaves them as adult sil ver eel. 



()-(iroui» (=^ Ist year's group). 



It has long been known, that small eels — about 70 mm. in length — 

 wander into our waters in great quantities in spring and early summer. They 

 have been observed even before they reached into the coasts; tbus A. C. Johansen 

 has found them pelagicall}' iti the North Sea and Skager Rak in March and 

 April 1905 and says on this in his above-mentioned paper: »the young metamor- 

 phosed glass eels are pelagic in the sea at night, whilst in the daytime they 

 remain at the bottom.« And C. G Joh. Petersen has likewise taken them pelagi- 

 cally at night in the bay near Kærteminde in April 1905. But they are only 

 seen in large quantities when they have reached the coasts, and especially during 

 their migration up into the rivers; as they are then forced together within a narrow 

 area especially where a barricade, for example at mills, obliges them to stop for 

 a time until they find a way forward. 



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