l895- ^O- 9- HYDR.-BIOL. 5TLDIES OF THE XORW. FISHERIES. 4 1 



Chapter III. 



Investigations of the Plankton. 



During each of the hydrographical investigations, and when the 

 weather has allowed of it. I ha\ e also endeavoured to collect materials 

 from the Plankton drifting organisms of animal and plant life\ During 

 the course of the last two years I have thus obtained a ver}- consider- 

 able amount of materials, gathered at all times of the year. Especially 

 from the West Coast has it been possible to obtain specimens during 

 almost all months of the year, whilst specimens from the Christiania 

 Fjord, and from the North, are but few. and have only been col- 

 lected, occasionally. 



On account of circumstances I have not been able to use Henscns 

 or Petterssoti 5 well known Plankton Apparatus, but was obliged to 

 construct a very simple net. the bottom of which consisted of fine silk 

 gauze. This net, at tlie commencement of each in\estigation was thrown 

 overboard, being towed by the ship so long as work lasted, and Avas 

 then hauled in. Naturally, with such primitive means, it was only pos- 

 sible to obtain specimens from the uppermost layers for entirely limited 

 investigations. 



Exact estimates of the quantity of the surface Plankton must, 

 as will be understood, also depend on the flow of the water, as a 

 drifting net must be presumed to be capable of collecting more Plank- 

 ton at one time in a strong current, than in more sluggish water, even if 

 the amount of Plankton in the sea is alike, as, in the first instance, a 

 greater cubic amount of water must, necessarily, be strained. Although 

 there are thus required accurate, and complicated appUances for an exact 

 determination of the amount of Plankton in the sea, I am of the opinion 

 that one may. with the very simple and cheap apparatus employed b}- 



