53 



organisms, evidently, cannot thrive, or find tlieir food, without a certain mini- 

 mum of light, while others seem to thrive better lu almost total darkness. Oii 

 less deep water, O — 30 — 40 fathoms, we meet with a temperature changing from 

 O — 19" C, 011 the greater depths c. 4 — 8" C. — Mauy animals will uot be able, 

 in certain periods of tlieir lives (for iustance in their breeding-time) to obtain 

 the sufficiently higli or Iow temperatures which are necessary for them, except 

 on louer water; others cannot bear tlie changing temperatures of the latter, 

 but are killed by it; they must remain ou the greater depths. The saUnity is, 

 near the surface, very changing; in the deepest regions exceedingly constant. 

 The specific gravity, which is chiefly dependent ou the salinity of the water, 

 seems also to be of some moment, as certain eggs of fishes cannot fioat in the 

 lighter water, and are therefore carried into the more saline, deep water. 



We must presume that also the pressiire of the tvater in the various 

 depths, and its contenfs of oxygen and carhonic acid, must be of essential im- 

 portance for the life of the animals; but it cannot be denied, it is very strange 

 that it is just between 200 and 300 fathoms the ditierence between the faunas 

 is so great, for down here most of the said natural couditions (the pressure 

 and the light excepted) are, no doubt, pretty nearly the samme. — It is my 

 couviction that the causes of the distribution in our seas of the various spe- 

 cies as a rule can be found in these and similar purely chemico-physical con- 

 ditions. A closer study of this matter, supported by experiments, would 

 throw light on many questions of merely theoretical as also of great practical 

 importance. — 



When we except the Norwegian fjords, which at certain piaces are very 

 deep (as deep as 700 fathoms), we shall look in vaiu in northern Europe for 

 a place as easily accessible as the Skager Rack for de study of the clarJc regions 

 of tJw sea; moreover the bottom is exceptioually convenient for fishing and 

 trawling. From the Skaw we have only 5 — 6 hours sailing to get out on a 

 depth of 3 — 400 fathoms. The Norwegian fjords, of course, are more conve- 

 niently situated; but the bottom is not so favourable, perhaps, at all piaces, 

 and their stagnant waters, shut in sometimes for many years, do uot offer 

 such oceanic couditions as the Skager Rack, whose waters, aoording to O. Pet- 

 tersson's investigatious, are frequently renewed. 



As to the frequency of the fishes in the seas investigated, we get by 

 the investigatious of the Biologicai Station, as a rule, ouly information with 

 respect to the smaller oues. As to the larger forms, however, the trawlers, 

 cspecially the German trawlers, eau give much information. It is stated every 



