42 
transform each single leaf to a »lamp-cleaner«. I consider these small, slime- 
forming algae a very essential component of the food of the animals which live 
in these regions, and Rauchenplat's investigations, which show among other 
things that the stomachs of Gastropods are filled with bottom-diatoms and pieces 
of algae in addition to pieces of Zostera, indicate just that this is the case. 
In 1899 K. Brandt wrote with reason: »Diese schnell sich vermehrenden 
kleinsten Pflanzen der Uferregion werden augenscheinlich starker gefressen, als die 
grossen Tangbusche und die kieseligen Seegriser.« 
Among all the dead oysters with the shells still connected I have fished 
up in this shallow water, I have only found two containing soft parts; all the 
others had been cleaned by the flesh-eaters such as AÅsterias and Gastropods, and 
this occurs very quickly, as direct experiments with cast-out, opened oysters have 
shown me. The two dead oysters with the soft parts were quite rotten and stink- 
ing, and were both found at the same time early in thé spring, shortly after the 
ice had disappeared, thus presumably before there was much life in the lower 
animals of the shallow water. Otherwise an opened oyster is deprived of all its 
soft parts in 24 hours, at any rate in summer; an index of how quickly and 
cleanly everything is eaten up which has any value as food. In these two plant 
belts live almost all the animals which Rauschenplat calls large-plant feeders 
and small-plant feeders, as also predatory animals and flesh-eaters.. Among the 
inhabitants of the plant belt I have sought in vain for animals, which contained 
plankton forms in their stomachs to any essential degree. The beautiful C/avellina 
lepadiformis which is always attached to objects above the bottom and might be 
expected to feed on such organisms, is always filled with detritus, in which however 
a quantity of Lamellibranch larvae, Tintinnids and other plankton may be found. 
There remains for consideration only the food of the true plankton ani- 
mals and the fishes. Among the latter there are but few, which as adults can 
be referred to the plankton-feeders, probably only the herring and sprat, which 
occur in quantities in the Limfjord at certain times of the year; there the herring 
also feed on bottom-forms, such as worms; I have not made systematic investiga- 
tions in this region in this connection"). 
With regard to the actual consumers of the plankton, there is still great 

£) In his paper (Chemische Zus. d. Planktons, 1900. pp. 45—46) Brandt states, that 
herring and mackerel feed almost entirely on plankton organisms, that Cyclopterus in the aquaria 
feeds on Aurelia; but even the other fishes, which eat larger animals, therewith take the plankton 
into themselves for the most part in altered form. The herring certainly eat, and perhaps mostly, 
Copepods but also many other forms with us; the stomach contents of Cyclopterus may also be 
said to be remains of Medusae; but most of the other economically important fishes certainly 
do not eat plankton, not even in altered form; it does not hold good in any case for the 
fishes of our waters. I have seen ÅAcanthias vulgaris in the Great Belt often filled with Pleuro- 
brachia alone, at times they eat the same in the North Sea, but at other times as known they 
take more solid food. I only mention this as an example of, how varied the food of fishes is, 
and to utter a warning against drawing widereaching conclusions, without numerous investigations 
in nature, with regard to what the different fishes mainly live on in reality in the different 
waters. That the larger animals, on which so. many fishes feed, should be regarded as »Plankton 
in altered form«, is such a general expression, that it is difficult to prove; it certainly does not 
hold good for the most of our waters: where and to what an extent it may prove to be correct 
is a work for future investigators. 
