73 
alba, Mytilus edulis, Solen, Astarte borealis, Cynthia, Idothea marina, Gammaridae 
ete. thrive excellently in it. For about 3 months the water has kept clear in a 
cool room. »Plankton« apart from bacteria is not present in the water; but the 
animals live well and Abra has grown considerably in the interval. The aquarium 
is 45 cm. long, 18 cm. broad and 31 cm. high. I have already made many new 
observations of great interest in this little aquarium, some of which have been 
already mentioned; and I expect that aquaria populated in the right way, will 
give much information regarding many of the questions, it is not possible to solve 
in open nature, and am inclined to believe, that through such aquaria we may 
find a way to make many experimental investigations on the animal life of the 
sea, especially in biological regards. One may wonder also, whether the large, 
public aquaria could not try to approach nearer to the natural conditions on 
the sea-bottom, so that the animals could find suitable conditions of nourishment 
in them; many of quite the commonest marine animals are never seen in such 
aquaria, simply because they will not thrive without the bottom-detritus. A 
certain amount of courage is required to place the dark, dust-fine mud from 
the sea-bottom in an aquarium; the whole water comes to look like undiluted 
mud; but after a time a change occurs, the water clears and the animals become 
satisfied with their surroundings. We must naturally take care, that there is a 
proper proportion between the bottom-materials, quantity of animals, quantity of 
plants and amount of water, but it is only by experiment that we can ascertain 
the right proportions. A suitable temperature is naturally also a necessity. 
After Petersen's earlier investigations on the oyster and other bottom- 
animals of the Limfjord had shown, what a slight importance in quantitative 
regards the plankton had for the nourishment of these animals, he began with 
Boysen Jensen a study of the dust-fine mass which usually forms the prin- 
cipal contents of the stomachs of the bottom-animals, which are not predatory 
or plant-feeders. 
The dust-fine mass is partly of inorganic, partly of organic origin, but 
quantitatively seen living organisms are seldom contained in it. AÅ study of the 
bottom-flora shows its extent and . distribution in the Limfjord and how little 
comparatively it is used in the living condition as food for animals; on the other 
hand, a close connection is shown between the density of this flora and the amount 
of organic matter contained in the sea bottom, from the North Sea to the Baltic. 
The enclosed fjords are richest both in hbottom-vegetation and organic material in 
the deposits of the sea-bottom; the quantity of the plankton here does not seem 
to have any recognizable influence. By means of bottom-samplers and glass- 
tubes it is shown, that the uppermost brown layer of the sea-bottom (ca. 
10 
