31 
exclusively on bottom-diatoms, not on planktom-diatoms; further, he sometimes 
found remains of copepods, larval worms, Noctiluca, Tintinnidæ and Radiolaria in 
the stomachs of the oysters, but the chief food was absolutely the bottom-diatoms. 
He found also that it was especially in the autumn and winter months that the 
vyster had much food in its stomach as a rule, whereas in summer during the 
spawning time its stomach was usually empty. I may add to this that the plankton 
is very scarce in the winter months, and most plentiful in the light season of the 
year, which agrees well with the described features of the oyster's mode of life. 
We can thus understand why the oyster only has a fat appearance and good 
flavour in autumn and winter, because it is then feeding greatly and collecting 
into its tissues a quantity of glycogen as a kind of reserve food. Thus, in the 
"warm season of the year only 6—8/, of glycogen was found in the substance of 
the oyster, but in winter 15—20'/,. The oyster spat must in any case however 
be said to form an exception to the rule, that the oysters feed specially in the 
cold season of the year, since the spat fix themselves in July—August and have 
already grown considerably under favourable conditions by September and October. 
The rules applies more especially perhaps to the oysters taking part in reproduction. 
Concerning the age and growth of the oyster in the Lim Fjord 
various opinions have been expressed; but actual investigation of the matter seems 
never to have been made. Eschricht estimates the oysters of 3—4 inches to be 
»at least 4 years old«, probably in agreement with Agent Steenberg. These deter- 
minations of the age rest merely on guess work, as we cannot see with certainty 
on the older shells how old they are, and this is difficult enough on the 2—3 
year old; certainly the zones of growth on the shells have something to do with 
growth-periods (years), but it is often not easy to determine them with certainty. 
I endeavoured therefore, already in 1895 and 1896 as well as in later years, partly 
by direct observation of the growth of the young on the collectors, partly 
by measuring all sizes of oysters on a bank, to determine the year-groups, as 
can be done often for other animals (measurement-method). The result of these 
observations is shown on Tables I—IIL On the two first (of older oysters) the 
measurements are given in inches, on the third im cm.; for the sake of accuracy 
I have retained the original measurements partly in inches partly in cm. 
The growth of the spat on the collectors can be seen from Table II, No. 
13—18. In August 1895 the young oysters were on an average !/, inch in dia- 
meter, in Sept. a little over ”/, inch; on Oet. 29th 1896 they had reached sizes 
between Z/, and 1%/, inches. The spat which fixed itself in the summer of 1896 
on a large welled-box used for the carriage of plaice (see pp. 25 and 26), reached 
in Sept. the same large size between 7/, and 1!/, inches, being on an average ca. 
1 inch in diameter. The young oysters on the collectors thus reached up to a 
little under one inch in the first year and up to ca. 1!/, the next year; but I am 
certain that this does not represent the normal growth of the young oysters in 
the fjord under ordinary conditions. The young oysters found on the banks in 
Sept. and Oct. 1896 (Bjørndrup and Langehage, see Table HM No. 12 and 10), 
were namely considerably smaller, only ca. ”/, inch. These two localities last- 
named lie in deep water (2—3 fathoms), whilst the young oysters from all the 
» 
