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ANNALES DE L'INSTITUT OCÉANOGRAPHIQUE 



it is impossible by their means to determine beforehand the distribution of the animals 

 in the sea ; it seems to me, that it would be far better to rely upon the distribution of the 

 characteristic animals, taking this in the sense in which I have used it here ; for it must 

 be supposed that also in other waters outside the Danish there must be such characteristic 

 animals or communities ; what I have hitherto seen in the North Sea at least gives me 

 some reason for this belief. From the literature not much information can be expected 

 in this matter ; the material of the large expeditions is generally divided up among many 

 specialists never to be collected into a whole again as regards the animal communities; 

 further, this material is not based on true quantitative investigations, but collected by 

 means of dredges, trawls and similar apparatus. 



Excellent preliminary work for true quantitative measurements have been carried 

 out in France during late years by Thoulet, Guérin-Ganivet and G. Pruvôt, in England 

 by Allen and Holt and in Scandinavia by Appellôf, Lônnberg and others; in these works 

 I often find representatives of several of the characteristic animals of the Danish animal 

 communities, partly occurring just as they do here. 



K. Môbius of Berlin is the one who first spoke of animal communities in the sea, 

 Biocoenoses he called them. Fr. Dall in Germany was the first to make quantitative 

 investigations on bottom-animals, namely in the area laid dry at ebb-tide, where the 

 animals could be dug up. 



Finally, it may be mentioned, that one of the most characteristic animal communities 

 of the world will certainly be the reef-building corals ; L. Joubin has already given some 

 beautiful charts thereof, but a quantitative investigation is still wanting ; it will possibly 

 not be easy to carry out. 



From the literature I only know one attempt at characterizing larger areas of the sea- 

 bottom by means of quantitative characteristic animals ; this is Johan Hjort*s expe- 

 riment with the fishes, based on the fishery statistics, by means of which we have 

 information of the relative frequency of a great many fishes, especially the food-fishes 

 in the different regions of the sea ; thus in his and Murray's book on The depths of the 

 ocean he succeeded in characterizing the fish fauna of the coastal banks north of Great, 

 Britain by means of their quantities of cod, haddock, plaice, etc.; south of Great Britain 

 Merluccius is the dominant species almost down to the north coast of Africa, and further 

 south other species occur in quantities. 



Hjort also mentions how long, narrow depth-belts along the coast of Europe are 

 populated by characteristic species of fishes, some living in deeper, others in shallower 

 waters, but the depth in which a certain species lives often changes with the latitude 

 (temperature andlightconditions);onpage423 he writes that on trawling at different depths 

 from shallower to deeper water, « we immediately recognise different strata, each charac- 

 terized by its peculiar fish-community. It will be of interest to define the extent of 

 these communities by means of the species found most abundantly ». 



If Hjort can already find out so much by means of the trawl and with regard to 

 the swiftly moving fishes, how much more should we not feel inclined to suppose that 

 this also applies to the slowly moving species of animals on the sea-bottom. Of great 



