ANNALES DE L'INSTITUT OCÉANOGRAPHIQUE 9 



representation ôfthe animal communities of the sea-bottom, the bottom-sampler has to 

 be used. Anyone who has used the dredge a great deal and under different conditions 

 must have observed the uncertain way in which it works ; we soon come to the result 

 that we can only rely upon what is seen in its bag, whereas one cannot draw the conclu- 

 sion that what is not found therein does not live on or in the sea-bottom ; on the other 

 hand, long series of investigations with the bottom-sampler show an exact agreement in 

 its contents, which also specially represent the very commonest animals of the sea- 

 bottom and not so much the large rapacious animals, which according to their nature 

 must be scarcer than the food on which they live. If however a complete survey of all 

 animals living at a certain place is wanted, it will certainly not be sufficient to use bottom- 

 sampler and dredge only, we must also use trawls of considerable size and other fishing 

 apparatus ; but this is not what we are wanting on this occasion, we are only dealing 

 with the true animal life of the sea-bottom, that which serves as food for other animals 

 and must therefore be supposed to be far superior to them in number and mass. After 

 this digression I may return to my original subject, the animal life of the sea-bottom as 

 represented by the bottom-sampler (fig. 9). 



I may now show some typical pictures of the animal communities in Denmark; 

 for practical photographic reasons, they only comprise the animals on o, 1 m 2 (the fig. 5-8). 

 The great difference in quantity with regard to the occurrence of the various species is 

 esasily seen from these pictures. They are not momentary pictures of the sea-bottom ; 

 such would only show a few of these animals, as they are mostly buried in the sand or 

 mud at the bottom, but the pictures show the number of animals and their true size in 

 relation to the area, but better information still is obtained from the numerical valuation 

 (see No. 20 and No. 46) (fig. 9). 



It is quite clear that in these quantitative valuations each species, whether numerous 

 or scarce, cannot be said to have the same importance for the characterisation, neither 

 of the content of the community nor with regard to the outer conditions under which 

 this lives ; on a moor the heather is more characteristic than the scarce plants also found 

 there. Firstly various species may be scattered as pelagic fry outside their true area of 

 occurrence, where they may live for some time but never become large and old. Further, 

 by the drifting sea-plants or in other ways single individuals may easily be carried away 

 to places where they do not belong and consequently perish in the course of time. I tried 

 therefore, to base a characterisation of communities on species of importance both in 

 regard to number and weight, but also on species, the individuals of which are less nume- 

 rous but evenly distributed and large in size. Look for instance at fig. 5, on which 

 Brissopsis lyrifera and Nucula sulcata together with Amphiura are the most frequent 

 animals. Brissopsis is not numerous, but, as shown by many samples, so regular in its 

 occurrence, that it is found in almost every m 2 inside its region ; the same applies to the two 

 other species. In other quantitative valuations (fig. 9, No. 46), Echinocardium has takenthe 

 place of Brissopsis, and among the Gastropods Turritella occurs as the most important 

 animal. Sometimes the quantitative valuations contain a fewlargeanimals, as for example 

 large rapacious Gastropods,. large rapacious Asterids, etc.; but they occur so seldom that 



T. VI. — Fasc. i. 2 



