The Relation of Mollusks to ish in Oneida Lake 119 
mation of hydrogen sulphide and rendering them fit for ani- 
mal life. Jensen aptly concludes that **‘ we may therefore. 
to a certain extent, regard the large oceans as the lungs of the 
sea, which supply the water-masses of the inner seas with 
oxygen and remove the superfluous organic matter.” In fresh 
water it is stated that humic acid probably has some intluence 
in preserving the dead plant material. 
Petersen has fully demonstrated that this dust-fine detritus 
forms a large part of the food of the oyster and other mollusks 
not of a predatory character. Dissection of the oyster showed 
the stomach to be filled with a substance in no wise different 
from the brown upper surface layer of the sea bottom. Cer- 
tain clams (Abra) confined in an aquarium were observed 
to suck up this surface layer with their long siphon. In addi- 
tion to the detritus of the bottom these animals also consume 
asmall amount of plankton organisms. Those animals which 
cannot take the detritus directly from the bottom utilize that 
which is held in suspension in the water which is said by 
Petersen to be greatly in excess of the pure plankton in 
quantity. The work of Lohmann, Hensen, Dahl, Brandt, 
Rauschenplat and others in the light of Petersen’s discoveries, 
corroborate the fact of the extensive use of the dust-fine 
detritus as food. Curiously enough, reference to this source 
of food in American works, on both marine and fresh water 
animals is all but entirely lacking and the writer has noted 
no reference to Petersen’s hypothesis in a recent work on the 
oyster (Stafford, 1913, p. 9) which states that the food con- 
sists of the smallest particles of material, the minute plants 
and animals called plankton, including diatoms, ete. A 
‘areful study of the food of marine and fresh water 
peleeypods, in the light of Petersen’s discovery, is greatly 
needed as suggested by Adams (1913). 
