10 



salinity suddenl}' increases. This layer thus forms a bouudary between tbe salt 

 bottom-water aud tlie less salt surface-M'ater. 



The information the tables give coucerning the direction aud rate of flow 

 of the surfacecurrent shows that the main tendeney is from the true Baltic towards 

 the North Sea. The movement of the deeper water-layers has not been iuvestigated 

 from the hghtships, but it is obvious, that the salt water at the bottom must have 

 its origin in the North Sea, and if not renewed fairl)' frequently, the bouudary 

 between the surface and bottom-water would quickly disappear; as a matter of 

 faet the bouudary usually remains very clear, as can be seen from the tables. 



There is tlierefore uo doubt concerning the truth of the following main 

 lule, known for a long period, for the movement in Danish waters: tlie water of 

 Jow salmiti/ from the triie Bnlfic tends outwards to the North Sea along the surface, 

 whilst a cvrrent of snit loater is going in the opposite direction from the North Sea 

 in fotvards the true Ualfic along tlie tiottom. 



The surface-water in the true Btiltie usually iias a salinity of Icss than 

 1 7oi i" tiis North Sea of 3 °/o and more, aud all trausitional stages are fouud 

 at intermediate piaces. This conditiou may be explained by the surface-ciirrent as 

 it passes toivards the North Sea taJcing up water from the under- cur rent. 



It will be readily understood, that the hydrographical conditions in Danish 

 waters have a great influence ou the distribution of pelagic organisms. I have 

 only described the main features of these couditious however, preferring to show 

 the deviations from the rule in their influence on the distribution and fate of the 

 pelagic eggs and young of iishes. 



Pelagic flsli eggs. 



The pelagic fish eggs are not evenly distriJiiited in the Danish waters nor 

 equally frequent at all times of the year. The Direotor of the Biologieal Station has 

 often remarked on this in his papers, amongst whicli special mention ma}' be 

 made of "De danske Farvandes Plankton, I" (Tab. VI— XII and p. 240—255) and 

 "Biol. Stat. Beretn. VII" (p. 15—18). 



In "De danske Farvandes Plankton, I" the Director discusses the planJdon 

 investigations of 1898 — 1901. These investigations, as mentioned previously, were 

 undertaken at several piaces in Danish waters, espeeially from Hghtships. Vertical 

 hauls with the pelagic net were made twice monthly and this work was continued 

 for two years (April 1899— April 1901). On Tables VI— XII of the work mentioned 

 the Director gives the number and as far as possible the species of the eggs and 

 youug fishes taken iu each single gathering. 



A comparisou of these Tables shows, that very few pelagic fish eggs were 

 taJcen in the Skager Rak and North Sea in Jantiary and February, that the numhers 

 incrmsed from January to June — Jnly, a few were stilll found in August, but none 

 at all in the following months until December when a single egg was takeu in the 

 Skager Rak. 



In the Kattegat pelagic eggs were taken in every month of the year. The numhers 

 rose quickly in the Jirst three months, miich more quickly than in the North Sea and 



