63 
calculating, the production for all the animals in Thisted Bredning mounts up to 
200 gm. of dry matter per 10 m.? per annum. To get a nearer approximation we 
must know exactly the growth and age of the separate animals; the large Cyprina, 
Buccimum and Nassa evidently grow slowly; of Asterias and Ophzroglypha too little 
is known in this regard. It is remarkable, that the numbers of Ophioglypha have 
been steadily and greatly decreasing from 1909 to 1910. 
Only Nissum Bredning in addition to Thisted has been so carefully 
investigated, that we can in any way judge as to the abundance of the food- 
animals; a comparison of the two is therefore of interest. Mya truncata has not 
been found at all in Nissum Bredning, but here Åserdiella and Echinocardtum are 
numerous especially in the autumn. The total quantity of dry matter in Nissum 
Bredning was 50.5s gm. per m.” in the spring, 12348 gm. in the autumn; thus, 
in spite of the many Holothurians and Echinoderms not half of what it was in 
Thisted Bredning (see Table V); but the fluctuation points to a fairly large annual 
production, namely of at least 72 gm. per 10 m.?; as shown in Table V, this is 
due specially to the increase of Ascidiella, but in smaller degree also of other 
animals. 
Thus we do not come in general to any very definite results in endeavou- 
ring to determine the production of the single species in Table V by means of 
their annual increase; much of it disappears owing to the efforts of fishes and 
other animals. I have endeavoured, therefore, always in principle in the same 
manner as Hensen, to determine how much the fishes in these waters 
annually devour. This amount which is eaten by fishes and other animals, must 
be added to the increase from spring to autumn, which is shown in Table V, in 
order to obtain an insight into the total production of the bottom-animals 
per annum. 
To be able to make such a calculation we must know, what quantities 
of food, for example, a plaice takes per day and per year, and I have 
long sought after a method of obtaining information on this point. I have thought 
of feeding the plaice in captivity, but soon gave up this idea as I foresaw that it 
would give far too uncertain results, which further would throw no light on the 
natural conditions in the open. I have endeavoured to catch the plaice with full 
stomachs and intestines and keep them in a well, until the contents were digested, 
so as to determine the time the process took; but the results from this were far 
too irregular; the plaice are easily damaged especially when the stomach and 
intestines are full of Lamellibranchs. I then came to the idea of catching the 
plaice at different times of the 24 hours, so as to see whether there was a diffe- 
rence in the quantity of food by night and by day, and thus if possible obtain 
some information regarding the quantity of food per 24 hours, and this method 
soon proved itself useful. I shall return to this below, but may mention here, 
that V. Franz in his work published in 1910, which I became acquainted with 
later, has made similar experiments to determine the food-capacities of the plaice 
at different times of the 24 hours in the North Sea, but he has not found that 
the digestive tract is emptied so completely as I have found in some of my expe- 
riments; perhaps because the plaice in the North Sea feed at night-time on the 
luminous Amphiura filiformis, which does not live in the Limfjord, but perhaps 
