74 
2—3 mm. thick) must be regarded as dust-fine detritus containing remains of 
almost all durable parts of organisms, but in the main its organic content is cer- 
tainly formed of deposited, dust-fine or larger parts of the plants from the ben- 
thos vegetation. Whilst the contents of this brown layer and its degree of 
oxidation make it specially well-suited as nourishment for the animal life of the 
sea bottom, the underlying layers are of quite a different nature. There is no 
recognizable difference between the stomach contents of the Molluses and the 
components of this uppermost brown layer. 
Centrifuging of Limfjord water shows quantities of dust-fine detritus 
in this of quite similar nature to that in the brown layer of the bottom. The 
quantity of the plankton organisms is inappreciable in comparison with the quantity 
of the dust-fine detritus. In several enclosed fjords with rich bottom-vegetation 
large quantities of dissolved organic matter have been found in the 
sea-water. 
The deposited detritus and its quantity have been studied by means of 
tubes (detritus-collectors) specially set out on the bottom; the quantity proved 
to be very dependent on the strength of the wind, as the motion of the waves in 
the shallow Limfjord, as a rule only 8—12 meters deep, can obviously stir up the 
fine soil of the bottom. 
A study of the literature shows, that at other places both in Europe and 
America similar contents have been found in the digestive canals of the oyster 
and other animals, but there has always been some hesitation in believing, that 
anything from the dead material of the sea-bottom could be of importance as 
food, partly because only the black, underlying mass of mud has usually been 
noticed when brought up by the dredge and thus the uppermost, thin brown layer 
has escaped attention, partly because one cannot directly see any difference in the 
detritus before and after it has passed through the gut of the animals. The 
American investigations on the quantity of living organisms in the gut of the 
oyster have shown, however, that this is so small, ca. 7/; mm.%, that in our opinion 
it cannot possibly constitute the food of the oyster. 
In recent years, however, Lohmann for the plankton animals and 
Rauschenplat for the bottom-animals have taken some notice of the detritus 
as food. 
To study the food of the bottom-animals we selected the whole of a 
restricted animal community in one of the most enclosed parts of the Limfjord 
(Thisted Bredning); here it appears that by far the majority of the animals are 
detritus-feeders and obtain the detritus partly from the water partly from the 
uppermost brown layer on the bottom, the origin of which is mainly of a ben- 
thonic nature. The plants of the plankton must rather be considered as serving 
as food for the plankton animals, but they are not always sufficient for this 
(Lohmann). The benthos vegetation must therefore be ascribed a very great 
importance as source of food, among others, for the benthos animals in the Lim- 
fjord. It is mentioned, that both Hensen and later K. Brandt have been aware 
that the plankton cannot alone supply food for all the animal life of the water, 
and it may be considered, that only the lack of methods før the quantitative study 
of the benthos has prevented them from also making such experiments. To 
