196 Prof. K. Mobius on the Nourishment of 



regions sink to the bottom after tliey have died, gradually 

 break up into smaller and smaller portions, and finally glide 

 down into the greatest depth that they can attain. The same 

 course is taken, as I know from personal observation, by the 

 vegetation in the bay of Heligoland, at those places where no 

 strong currents of ebb and flow prevent the deposition of 

 organic masses. 



This organic and chiefly vegetable mass, in the particles of 

 which we may often still recognize cellular structure and 

 demonstrate the presence of cellulose by iodine and sulphuric 

 acid, is what renders the mud-region inhabitable by a great 

 number of animals — in the first place, by those which feed 

 upon decaying matters, and then for others which devour the 

 dirt-eaters. In this way we find it easy to explain the quan- 

 tities of individuals, at the first glance quite astonishing, 

 which may be got out of the mud of the greater depths ; for 

 the mass which serves them as a dwelling-place at the same 

 time contains an enormous store of nourishment for them. 



The same thing must take place in all seas. In the shal- 

 lower regions which immediately surround continents and 

 islands, great masses of Algse grow wherever there are rocks 

 and stones. In the warmer seas there is an enormous floating 

 Sargasso-life. Only a small portion of these plants is directly 

 eaten by animals or thrown upon the shore. Most of them 

 die where they have lived, or, after they have been carried 

 away by currents and winds, lose the gases which make them 

 lighter than sea-water, sink down, and finally become decom- 

 posed into a soft mass. In such a state as this Wallich found 

 considerable quantities of dead plants, in depths which 

 extended beyond' 500 fathoms (North-Atlantic Sea-bed, 

 p. 130). 



With the sinking organic materials are, of course, inter- 

 mixed the remains of Testacea and the fine inorganic soil- 

 constituents of the higher regions, which the currents of flood 

 and ebb and the waves are unceasingly triturating. This 

 muddy mixture must move down towards the deeps upon the 

 sloping sea-bottom in the neighbourhood of the coasts, from 

 purely mechanical causes, until the weight and mutual adhe- 

 sion of the individual particles present so much resistance to 

 the pressure of the masses following them from above that 

 equilibrium is produced. 



For the purpose of accurately testing the causes by which 

 sinking materials are moved down in a water-basin from the 

 higher to the lower regions, I made some experiments with 

 two rectangular aquaria. The space for water in the smaller 

 one (fig. 1) was 15 centims. long, 10 centims. broad, and 



