34 
shows that it is the detritus on the sea-bottom, which in any case at 
times is the principal source of the detritus deposited in the detritus- 
collectors. 

V.. Food of the animal life, especially in Danish fjords. 
It is many years since I first dissected oysters in the Limfjord in order 
to study the contents of their digestive organs; I imagined that they must live on 
the plankton which is so rich at times, but I was always extremely surprised to 
find their gut filled with an indeterminable, fine-grained, grayish or 
brownish mass, in which could be seen relatively few diatoms (mostly bottom- 
forms), a few Peridineæ, annelid bristles, spores, bristles of Crustacea etc. The most 
common organism after the bacteria is clearly Prorocentrum micans, but only a 
slight importance can be ascribed to it, so far as mass is concerned. 
I have investigated these conditions at different times of the year from 
March to November; in the true winter months there seems on the whole but very 
little in the gut of the oyster. 
The indeterminable mass cannot be distinguished in any essentials from 
the dust-fine detritus, »00ze«, which is found on the bottom where the oyster 
lives. We now know, indeed, that detritus forms the uppermost brown layer 
on the bottom of the whole of the Limfjord outside the plant belt. No recognizable 
difference has ever been seen between the organisms in these detritus layers and 
in the contents of the gut of the oyster, but the larger objects in the layer at the 
bottom naturally do not occur in the oyster. The quantity of organisms in the 
gut and stomach of the oyster is so small, that I must consider it as certain, that 
its food mainly consists of the organic parts of the detritus. It is 
possible, however, that the oyster at other places, where the quantity of detritus 
is less than in the Limfjord, may find its food, for example, mainly in diatoms or 
other small organisms. In Holland Redeke in 1902 showed similar conditions 
regarding the food of the oyster, especially that the material in its stomach had 
almost nothing to do with the plankton forms at the spot. Redeke 
describes a similar condition in Mytilus edulis and Åscidiella aspersa. He comes 
to the conclusion, however, that the diatoms are the main food, and not the 
»donkergrijze drabbige Massa«. Whether it is the one or the other which in 
reality is the main thing, will certainly depend on which contains the most acces- 
sible food; both presumably are of importance in this connection. So long as we 
do not have direct investigations on what the oyster really can digest in its 
stomach, I am of the opinion that we must have regard for both the detritus and 
the living organisms in this. Lotsy (Rep. U. S. F. C. for 1893, pp. 375—386) 
refuses all importance to the detritus as food, because it apparently passes 
through the digestive tract unchanged; hut it seems to me that there is absolutely 
no justification for this view, an exact examination is wanted. In the American oyster 
Lotsy found, in addition to diatoms, at least just as large a mass of »decaying 
