50 JOHAN HJORT. M.-N. Kl. 



The tables do not contain a list of all the specimens, as numerous 

 samples contained, in all main particulars, similar materials but, on the 

 other hand, those have been selected which, according to our experience 

 proved to be most typical of the season concerned. 



That which, first and foremost, strikes one on a superficial glance 

 at the tables, and still more from the specimens collected, is, that the 

 Plankton varies to the greatest extent both in quantity and quality at 

 various periods. One can perceive this alone from the colour of the 

 spirit in the glasses, which from some specimens is of a strong dark 

 brown or yellowish hue, in others almost colourless, in others, again, of 

 a clearly green tint, all according to the colouring matter of the pre- 

 served organisms. 



There is also a circumstance which is generally known to our 

 fishermen, that there are often »growths, animalcules, phosphorescence« in 

 the water, w^hilst it at other times is quite clear, so that the bottom may 

 be seen at a great depth. 



The conditions on which the periodical appearance of the Plankton, 

 depend are many and various. Although these have been repeatedly ^ 

 pointed out, I will, nevertheless, in a few words refer to them here. 



In the front ranks: — 



1 . The propagating period of the various organisms plays a great part 

 (which must, surely, be presumed to be dependent on the hydro- 

 graphical conditions). During the Spring and Autumn, excessively 

 large quantities of Plankton are to be found, consisting to a great 

 extent of various forms of larvæ, amongst which, especially, 

 those of Molluscs, Annelids, Crustacea, Echinoderms, Bryosoa, whilst 

 Copepods appear to propagate throughout the entire year, as Nait- 



piius is to be met with amongst almost all the samples, though in 

 varying numbers. From the appearance of the larvae. Dr. Petters- 

 son has been enabled even, to divide the year into various periods 

 which appear to correspond exactly »to the seasons on the land.« 



2. Of a more incidental character are zvind and variations oï light. Sars 

 says, as previously mentioned, »that only during the height of Sum- 

 mer, and when the sea is dead calm, is the prey ^ to be found 



1 I refer for instance to C. W. S. Aurivillius: Animalsk Plankton. (Animal Plankton.) 

 Bihang till (Appendix to the) k. svenska vet. akad. handl. bd. 20. Afd. IV. as well as 

 to C. G. Joh. Petersen: Beretn. til indenrigsminist. fra den danske biol. stat. 1892. 

 (Report to the Minister of the Interior from the Danish Biol. Station. 1S92.) Copen- 

 hagen 1893. 



2 Norwegian »Aate« =3 Prey, Food of Fishes). 



