18 
Transactions of the Society . 
the following structure : — In the centre a nucleus, which consists 
of two dark opaque rings or zones very close together, which are 
formed during the first period of life in the sea, and Haempel calls 
them “ Seewasserringe,” or sea-water rings, for this reason (fig. 7). 
These figures were drawn from otoliths examined by dark- ground 
illumination ; the dark zones appear whioe. 
In many otoliths the central nucleus looks like a thick dark 
ring, and the two zones only show after grinding down. Next 
comes a broader light zone, which is formed during the first 
summer after its arrival as an elver on the coast. 
The transparent elver during the development of the pigment 
suffers a reduction in length and volume, and the first definite 
growth begins when this is ended. 
The broad light zone is followed by a narrow dark opaque zone 
formed during the first winter, when the growth is slower, and, 
according to the age of the eel, we would observe a lesser or greater 
number of zones, light and broad summer, dark and narrow winter ; 
these indicate the age of the eel from the time of its arrival as an 
elver on the coast (fig. 8 represents the otolith of a silver male 
belonging to the group VIII). 
Thus the groups 0, I, II, III, IV, etc., mean that the eels in 
question have 0, 1, 2, 3 and 4 dark winter zones on their 
otoliths. 
The last exterior zone is only to be counted if completely 
formed. Naturally if we refer to an eel belonging to, say, the 
group V, it is really in its sixth year. 
There is always a difference between the number of zones of 
the otoliths and those of the scales. 
In the first place the scales only appear when the eel is about 
16 cm. or about 6 in. long at least, sometimes even when the eel 
is 18-20 cm. or 7-8 in. long. 
It is obvious that as the growth of the eel varies in different 
localities, the initial difference varies also. The scales may appear 
in the second or third year, or even perhaps later, according to the 
localities. 
If subsequently the zones on the scales were formed regularly 
each year, we could find out the age of the eels of a given locality 
by adding two or three, etc., to the number of zones, having 
previously found the age in which the first scales appear. 
Unfortunately, this is by no means the case, and in eels of a 
certain age the initial difference of the 2-3, etc., may greatly increase. 
I have seen eels of 40 cm. which had only two zones on the scales, 
and even cases where there were no zones at all. The otoliths 
would have had probably seven zones or more. Personally I 
believe that the difference (D) between the number of zones of the 
otoliths and the scales does not remain constant during the life of 
