The Relation of Mollusks to Fish in Oneida Lake 117 
While studying the samples of bottom brought up by the 
o.lm* sampler, Petersen observed that the bottom layers were 
of two kinds, the first, in which life was abundant, being 
brown or gray in color, the other being black and giving off 
an offensive odor. This was either very poor in, or devoid of 
life. Previous investigation had shown that the digestive 
tract of the lower animals which were not predaceous was 
filled with a brownish mass almost identical with this top 
layer covering the bottom of all the waters where it was suf- 
ficiently still and deep for the fine particles to be deposited. 
Petersen concluded that this material, which he called ** dust- 
fine detritus”? forms a large part of the food of bottom 
dwellers, such as clams and snails. This detritus consists of 
‘dead, deposited particles of plants and animals, among 
which we comparatively seldom find the remains of plankton 
organisms. Living microorganisms are naturally also found 
in the stomachs, but usually only in small quantity. We 
have so long and so often heard of the rdle the plankton is 
considered to play in the economy of the sea, that we almost 
forget the other sources of food, which however, at any rate 
in the smaller waters, certainly have an even greater import- 
ance’ (Petersen, op. cit. p. 6). 
Petersen’s colleague, Dr. Jensen, after investigating the 
source of this dust-fine detritus, concludes that its origin is 
primarily from the plants in the sea, principally the grass- 
wrack, Zostera. Thus it is evident that the dependence of 
animals upon plants for nutrition is as vital in the water as 
on the land. The plankton, either plant or animal, was also 
found to play but a small and unimportant part in the forma- 
tion of this detritus deposit. The marine plants die and 
either fall to the bottom where they grew or are transported 
to the same location in some other part of the sea bottom. 
This material breaks down until it forms the dust-fine detritus 
described. 
Jensen’s law that “the organic materials do not remain 
‘at the place where they were produced but are distributed 
more or less uniformly over large areas” is quite as appli- 
cable to large lake bodies as to marine bodies of water. This 
