45 
pp. 16—17). Walter certainly endeavours, so far as I understand him, to insert 
an intermediate link between detritus and the Crustacea, namely »die allerkleinste, 
mikroskopische Algenflora»; but he only does this partially; older investigations 
(Knørrich) show, that the Daphnidae can live and propagate in sterilised solu- 
tions,, where such algae do not occur. (Knauthe's book 1901, pp. 152—153). 
Thus, a complete understanding of the dust-fine detritus does not seem to have 
been reached for the freshwater either, but the matter has been much further 
advanced that for the salt water; here investigations have been too one-sided. 
It often happens indeed, that a line of study becomes more one-sided than 
its discoverer originally, in this case V. Hensen, intended. On reading his first, 
great. work on plankton of 1887 we see, that he had indeed considered the possi- 
bility that the sources for the food-stuffs of the sea are also the rivers and the 
coasts (p. 1); but he does not ascribe any considerable importance to this source, 
because: »ich finde nåmlich thatsåchlich nur eine sehr geringe Menge treibenden 
Materials, welches von den Kiisten herstammt«, and further: »weil, soweit mir 
bekannt geworden, iiberhaupt nur sehr wenig Thiere von abgestorbenem Materi- 
ale leben.« 
We may remember, that it has only been in recent years, that the quan- 
tity of dust-fine detritus in the sea-water has been demonstrated by centrifuging, 
it is only from this that its importance for animal life can be properly understood 
and estimated. 
On the page cited Hensen defines the plankton as »Alles was im Wasser 
treibt, einerlei ob hoch oder tief, ob tot oder lebendig.« Judging from the words 
this definition also embraces the dust-fine detritus; hut this was not known at 
that time; if we reckon all floating detritus to plankton, then this comes for the 
most part just from the coasts at certain places, that is the animal and plant life 
of the bottom, and is thus something quite different, in its origin at 
any rate, from the benthos. 
lf we also reckon the dust-fine detritus, coming from inter alia the benthos 
plants, to the plankton, then we must expressly admit this and remember, that 
this detritus is found both in the water and on the bottom, as also that it may 
be present where no other nlankton is found; it was certainly present for example 
in Hensen's aquarium, and may be produced by the organisms by the bottom 
alone. Nor in the future should the word plankton be used without defining 
exactly what is intended therewith (net-plankton, nannoplankion or detritus-plank- 
ton), or without remembering that benthos and plankton in any case at many 
places are closely connected. The hbreeder of carp who does not take into suffi- 
cient consideration the role the vegetation of the bottom plays, will certainly come 
to regret it. 
Though Hensen thus believed, that dead organic material served the 
animals for food only to a small degree, and that the vegetation of the coasts is 
of small importance as source of food compared with that of the plankton, he is 
one of the few who has really made experiments to study the matter closely. He 
writes for example loc. cit. p. 10i, that »Die Erzeugung des Meeres an der Kiiste 
muss eine sehr bedeutende sein«; by digging in the sand at low tide he found 
incredible masses of lower animals on small areas: »es muss hier eine sehr grosse 
