37 
probably makes use of the animals and plants it may find among the detritus in 
smaller or larger number. The many annelid and copepod bristles and other hard, 
small parts of animals and plants, as also the siliceous parts of plankton diatoms, 
found in the detritus of the stomachs, have undoubtedly contributed to spread the 
belief, that many animals feed on the plankton; most.of these remains must rather 
be regarded however as parts of the detritus itself, as it is obviously only after 
the organisms have died and sunk to the bottom, that they have been eaten along 
with the rest of the detritus. 
The impression gained of the nature of the bottom from dredging has 
certainly also contributed to the belief, that the detritus of the bottom was useless 
as food; the often black, stinking layers of mud, which lies under the uppermost 
brown layer, is what strikes the eye most; and they are probably indeed of no use 
as food for higher organisms. On being stirred up into the water, however, they 
very soon change their character and colour, a fact I have been able to observe, 
for example in aquaria, That one cannot detect the difference between the 
dust-fine detritus in the stomach and gut of the animals, also gives the impression 
that it is not digested (Lotsy); Rauschenplat rightly replies to this, however, 
that such a difference cannot be seen either in the animals which are known to 
live on detritus, as certain Gephyreans and other worms, loc. cit. p. 93. Rauschen- 
plat cites Mo bius, who in 1871 already had written, that the Lamellibranchs in 
the Baltic feed on »Moderteilchen der toten Pflanzen«; this was before attention 
had been directed to the importance of the plankton. Måbius' view was thus 
unbiassed and certainly in many cases more correct. See also Mobius: Iste Ber. 
Wiss. Untersuchungen. Kiel. 1873 p. 139. 
It is certain that no other detritus-feeding animal has been so carefully 
studied as the oyster; we know much less about the other detritus-feeding 
animals in our fjords, therefore, but that there are many of them, is undoubted.F) 
In Rauschenplat's paper we find good information regarding stomach contents 
of the animals occurring in Kiel Bay. He refers certain worms, among others 
Arenicola and Pectinaria belgica, as also Diastylis Rahtkir among the Crustacea, to 
the true detritus-feeders, further though with doubt Ophioglypha albida. To the 
plankton-feeders he refers Awrelia, Balanus, Mysis, Ascidians and a number of the 
commonest Lamellibranchs; but he adds: »reines Plankton habe ich nur ganz 
vereinzelt in den verdauenden Kavitåten gefunden« and he empasizes this statement 
in print; he also states expressly that he often just in the plankton-feeders finds 
an »unkenntliche Masse« in the digestive tract: »Ob es sich um Verdauungspro- 

£) I do not wish to leave this questition of the food of the oyster without referring to 
the »green oysters«, which are found in France and various other countries, and whose green 
colour in several parts of the body, especially the gills, has been placed in connection with the 
occurrence of certain green plants, in France Navicula fusiforme var. ostrearia, on which they are 
supposed to feed. Referring simply to one work on this subject, the literature on which is very 
great, namely Herdman and Boyce: Oysters and disease (Lancashire Sea-Fisheries Memoir, Nr. 
1, 1899), I may mention, that it seems as if oysters are coloured green in several ways and not 
always by the same substance; and that it is not settled, that the green colour comes from 
organisms which have passed through the digestive canal of the oyster. It does not seem to 
have been rigthly investigated what the oyster really has in its stomach; the green colour 
especially cannot with certainty be said to come from digested diatoms. 
