HYDROGRAPHY. 



J 59 



asf—c only is cri against the plankton-indication 2 V. + 4 A. We have now stations 125 and 133 left, 

 at which/— e relatively is 1-4 and r8, the plankton-indication of which is respectively 4 A. and 4 A + 4 Pk., 

 both with the remark: small quantity. This state of matters may be accounted for by the fact of its 

 being specially vegetable plankton that has been predominant at these stations, shortly before the 

 analyses took place. 



The mean-valne oi/—c for all the stations where animal plankton has been predominant, is 

 equal to — 075, which, as will be seen, is a negative quantity. The cause of this mean not having 

 a larger negative value is evident, when we take into consideration that animal plankton would 

 hardly be able to exist for a length of time at a place, if there was not at the same time vegetable 

 plankton, from which, at any rate, some of the animals could get their nourishment. It is a matter 

 of course, therefore, that even if we find pure animal plankton at a station, there must shortly before 

 that time have been vegetable plankton. We cannot, therefore, because we meet with exclusively 

 animal plankton at a place consider it as absolutely granted that an incomplete saturation of the 

 water is existing at that place. 



In accordance with the experiment concerning the influence of the diatoms on the gases held 

 in sea-water, I made another experiment with the copepoda to examine how great an influence they 

 exercised. The copepoda were caught in a large vertical-net, and filtered through a net of wide mesh, 

 on which they were deposited in a litre-bottle filled with sea-water. After they had been left 3 hours 

 and 17 minutes in the said bottle, the water with the copepoda was analysed. The result of this 

 analysis, stated in the table below in proportion to the volume of gases contained in the water before 

 it was poured on the copepoda, was as follows: 



V. Bottle with copepoda 

 VI. — without — 



Copepoda consume . 



ccm. C0 2 

 per Litre 



44'3 

 40-6 



-37 



ccm. N 2 

 per Litre 



12-36 

 12-29 



ccm. 2 

 per Litre 



279 

 6-70 



39 1 



100 O2 

 N 2 +0 2 



18-4 

 35-4 



The number of copepoda used for this experiment was about 2000 times larger than the 

 amount of these in the same volume of water in the sea. Still it is to be observed that this indication, 

 like the one concerning the experiment with diatoms, is to be regarded as rather unreliable. It will 

 be seen that at the same time as the quantity of oxygen has been considerable decreased by the stay 

 of the copepoda in the water, the amount of carbonic acid has increased, but not in the same ratio, 

 as the quantity of oxygen has been subject to the greatest alteration. 



According to these experiments, it must be considered as an established fact that the quantity 

 and nature of the plankton has a great influence on the amount of oxygen contained in sea-water. 

 If for all that we have met with quantities of oxygen — at several places — which could not be 

 ranged under the above mentioned system, the cause of this apparent discrepancy must of course be 

 accounted for by the fact of the plankton being subject to changes in so far as quantity 

 and quality is concerned, at certain places and in a given body of water, which 



