1 895- ^'ö. 9. HYDR.-BIOL. STUDIES OF THF. NORW. FISHERIES. 69 



at a like result and b}" carefulh" pouring a somewhat fresh solution of 

 salt into a glass containing a salt sample of sea-water, I could see the 

 eggs sink through the fresher mixture, and remain suspended a trifle 

 under the ver\- conspicious owing to the ditterent refraction) surface 

 boundar}- of the two waters. 



In connection with this I may add that Danncvig ^ of the Fish 

 Hatching Institution at Flodevigen, has repeatedly stated in his reports 

 that, when the water was cold and fresh, all the eggs and {x\ la}- on 

 the bottoms of the apparatus; they .stuck to them and perished. Peter- 

 sen states that, doubtlessh", in a natural state, great numbers are lost in a 

 like manner. 



The distribution of the eggs of pelagic fishes, therefore, follows 

 the same laws which govern all the Plankton see Chap. Ill), it is 

 dependent on the amount of saltness and the currents. 



From the results derived from the cruise of the Danish Gunboat 

 Hauch- -, it is proved that this is, likewise, the case in respect to many 

 of the forms of animal life which remain fast on the bottom, but which, 

 in the form of lar\a. lead a pelagic life. The spread of such animals 

 appears to be entireh" dependent on certain ordained physical factors. 

 Of the very numerous and most interesting examples I will take one 

 from Petersen's work, namely the Oyster. 



>Tn the onh* Danish Fjord, <^ says Dr. Petersen 3, in which the saline- 

 ness exceeds 3 per cent., namely, the Lim Fjord, there lives the 0}ster, 

 but only in those parts of it where the amount of salt is over 2.5 per 

 cent., and, as a rule above 3 per cent., and where the salineness falls 

 to near 2 per cent, no oysters are to be met with. When the Lim 

 Fjord, previous to the breach being made at Agger in 1825, was a 

 Fjord o{ the Cattegat, no oysters dwelt in it, but, after that, the oysters 

 made a rapid appearance, as well as all other kinds of southern and salt- 

 sea species.* >>This,« he adds, appears to me to be a direct experiment, 

 on a great scale, of Nature herself, which shews that this fauna desires 

 the sway of the ocean — in fact, cannot do without it. In those places 

 beyond our Fjords, for instance in the Cattegat where o\sters constanth' 



1 See. Indberetuinger over udklaekningsanstalten.« virksomhed. (Report on the Working 

 of the Fish-Hatching Institution). 



- See. C. G. Joh. Petersen: Nogle almindelige resultater. Kanonbaaden »Hauchts togter, 

 Kjobenhavn 1893. (Some General Results. Cruise of the Gunboat »Hauch«. Copen- 

 hagen 1893). 



^ Sec p. 464. 



