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on and in the level sea-bottom and form communities which are almost as easily charted as 

 the different kinds of bottom deposits, but others only occur on stones or plants which are 

 often found in patches and so scattered on the bottom that all charting, at any rate in 

 detail, is impossible; we cannot chart each stone on the bottom of the sea. Within several 

 of the communities of the level sea-bottom we have such anepifauna attached to stones, 

 shells, plants and similar objects; the animal contents of this epifauna differ of course in 

 deep and shallow water; the animal communities at such places consist of a double fauna, 

 one belonging to the launa of thelevel sea-bottom, the other to the epifauna. In flowing ' 

 waters the epifauna may be exceedingly luxuriant, so that the bottom may be covered 

 with large Modiola or Mytilus and their companions, worms, Echinoderms, etc. Such a 

 rich fauna would never be able to thrive on a level sea-bottom, as it requires a constant 

 supply of detritus, which constitutes the main nutriment of these animals. 



In the shallowest waters we find various epifaunas that are connected with the diffe- 

 rent geological nature of the coast and the costal plants etc. ; it is exceedingly difficult to 

 chart them, but in deeper waters there seems to be greater uniformity; epifaunas may 

 also occur here, they are charted when found. 



In the modern descriptive plant-geography we have a parallel to these epifaunas, for 

 example on a moor on which there are stones; these are covered not by heather but 

 by species of lichen and thus have quite a different plant community than the formation 

 in which they are found. 



If we have once become clear as to the double nature of the fauna, caused by objects 

 that do not belong to the level, ordinary sea-bottom, we can easily understand that the 

 bottom-sampler sometimes may bring up quite different contents from places lying quite 

 near each other. 



The quantitative determinations carried out in Danish waters show, that certain 

 species are more restricted in distribution than others, and some may be present in 

 many, almost all animal communities though not as characteristic animals but only 

 as accompanying species ; it is also seen, that there is a great agreement between the 

 distribution of the animals and the depth, the kind of bottom, the hydrographical con- 

 ditions, especially the salinity, which from the North Sea to the Baltic varies from 3,5 

 to o,5 p. 100. The physical conditions are evidently of great importance for the distri- 

 bution of the species; but also the biological factors, such as the relations between the 

 species, must be taken into consideration in order to be able to understand the occur- 

 rence of the communities. It would lead too far here to enter further into this question, 

 but I mention it because I find it quite wrong, that some of the more recent, marine 

 zoogeographers wish to base the division into zoogeographical provinces, regions or 

 zones on the outer conditions alone. I can much better sympathize with the authors, 

 such as E. Forbes, Lorenz and others, who tried to characterise various geographical 

 regions according to their content of animals. 



The physical conditions may afford good hints to zoogeography, because on broad 

 lines they are better known than the distribution of the animals, but there may exist so 

 many combinations of outer conditions, all of which may influence the distribution, that 



