32 



of our appreheusion oi' the distribution of the fishes, and as, from this very 

 reason, it uuderlies the arrangement of the various sections of this treatise. 



The coudition of the bottom is, in part, decisive of the lower animal life 

 on the bottom of the sea, and through tliis also of the stoek of fishes, as most 

 fishes arcniore or less attached to the bottom, i. e. stay uear it, and seek their 

 food among the lower forms of animals living in or on the same. 



In au open sea hke the northeru Cattegat it seems, particularly, to be 

 the depths which are decisive of the occurrence of the various bottom-species*) ; 

 that the same holds good also of the distribution of the vegetation is likewise 

 a well-knowu thing. The piants must have light in order to assimilate; but as 

 the light, in a great measure, is absorbed by the water, less and less light will 

 reach the bottom as the depths become greater. Some sea-plants demand more 

 light than otliers, from which reason their depth-limits do not agree; but 

 already on proportionally low water every trace of attached piants disappears. 



The various species of deposits, and the appearance and disappearance 

 of the vegetation as the depth increases, niay, in its main features, be described 

 as foUows: 



On quite shallow water, along the open shores, where the surf is strong 

 and the whole sea in almost incessant motion, the bottom generally consists of 

 unmixed sand, gravel, or stone. The motion of the water is too strong to per- 

 mit piants as the zostera, which grows in the loose sand, to get a footing, and 

 only where there are stoues we find a few bushes of bladder-wrack attached 

 to these. The sand-hanlis are therefore, generally, a locality**), barren of vege- 

 tation and rather destitute of nourishment. — Already on a depth of c. 1 

 fatliom the zostera begins to get a footing, and most frequently we find this 

 plant covering the bottom within a helt which reaehes out on 6 — 7 fathoms, 

 where the want of light prevents its going farther. The bottom where the 

 zostera grows consits also, chiefly, of sand, although as light formation of mud 

 may take place on particularly protected spots, in hollows and in shelter of 

 the stones. This locality, consequently, yields food and hiding-places for a mul- 

 titude of herbivorous, lower animals; its biological conditions are, on the whole, 

 widely differeut from tliose of the sandbanks nearer the shore. — Outside the 

 zostera belt, where the water is getting deeper, we still meet almost unmixed 



•) C. G. Joh. Petersen: Loc. cit. pp. 433—35. 

 **) Locality is used herc in the sense in whicli it is often uaed by botanists, to 

 indicato placcs of the same physical conditions, sueh as siiccies of deposits, depth, vege- 

 tation, etp. A locality mav theiofore very well be extended over several S(inare miles, or 

 its various pai'ls mav lie sitiiated near to or far from one auotlier. 



