l895- ^'O- 9 HYDR.-BIOL. STUDIES OF THE XORW. FISHERIES. 53 



ver\- great numbers of Diatomaceœ were found, which were not met 

 with at any of the surface trials. This too holds good in respect to 

 Sagitta at Station 114. 



If one compares this circumstance with the observations made in the 

 Christiania Fjord during November 1893, it will be found that, whilst in 

 1893, the Diatomaceœ went far into the Christiania Fjord, and rose high 

 up towards the surface (o to 10 mètres) they were first met with in the 

 following \ear several miles south of Fredriksværn, and there only at a 

 somewhat considerable depth. 



This circumstance agrees to the greatest extent with the hydrogra- 

 phical conditions. In the Autumn of 1893, ^^^^ Bank Watei- ran far up 

 the Christiania Fjord, in between all the Islands off Tonsberg, while during 

 the Autumn of 1894, the Baltic Current ran as a deep layer along the 

 East Coast, and onl\- down in the deep did the Bank Water force its waj^ 

 into the Christiania Fjord. This naturalh* explains the great difference 

 in the specimens of Plankton of the two years. The one set consisted 

 paramountlx- of Diatomaceœ, the other of Cilioflagellata. To what ex- 

 tent the hydrographical conditions may also thus explain the difference 

 between the Plankton of Summer and that of Autumn; to what extent, 

 too. the existence of the Diatomaceœ {Chætoceros^ is bound to the 

 .salter layers, and therefore, during the Summer, not to be found in the 

 fresh Baltic surface layers, I dare not express an opinion so long as the 

 cycle of life of these forms is so little known, but it appears to me most 

 probable from the consistent conditions in this instance, that the diffusion 

 of these organisms must be dependent on water of great salineness. 



As a proof of how different the Cilioßagellata Plankton and the 

 Diatomaceœ Plankton proved to be, I may add that the first was easily 

 distinguishable from the strong brownish-yellow colour it yielded to the 

 spirit in the tube, whilst the spirit in which the specimens of Diatomaceœ 

 were preserved was of a strong green tint, so that the specimens could 

 thus be distinguished from each other at the ver\' first glance. 



The Wintej' of 1894, was distinguished by an abundant, predominant 

 animal Plankton, with numerous pelagic eggs and forms of Lar\'ae 

 (Fishes" eggs, Gadus, Pleuronectidae , Eggs of Moluscs, Annelidœ, Bryo- 

 soa, Larvœ of Echinoderms, as well as Calatiida, of which Calanus fin- 

 mar chicus was by far the most numerous. As a rule Sagitta was pre- 

 sent in numbers. But few Cilioßagellata were met with, but, on the 

 other hand, great numbers of Diatomaceœ, especially, and above all, 

 some species of Coscinodiscus as well as CJuctoccros decipiens. 



