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Microscopic Marine Organisms in the Service of 



Hydrography.* 



By 



Professor P. T. Cleve, 



University of Upsala. 



It has for a long time been known that the sea abounds iu 

 microscopic organisms, both animal and vegetable. Among the former 

 are entomostraca, infusoria, radiolarians, foraminifera, as well as larvce 

 of mollusca, radiates, and bryozoa. Among the plant-life the mass 

 consists of diatoms, cilioflagellates, flagellates, and certain unicellular 

 chlorophyllaceous algfe. For these pelagic forms Prof. Hensen has 

 proposed the name ijlanhton, which has been universally accepted. 



Some years ago I examined the samples of vegetable plankton 

 collected by the Swedish Arctic expeditions, as w^ell as samples from 

 various parts of the tropical seas, and I became convinced that certain 

 parts of the oceans are characterised by different species. In the year 

 1893 I spent the summer at the west coast of Sweden, where I had the 

 opportunity of examining the plankton at the marine biological station 

 of Christineberg ; that is to say, in a fjord (loch) called GuUmarsfjord. I 

 found that in the month of June the plankton consisted mainly of 

 cilioflagellates, Ceratium tripos being the most common. During the 

 last days of the month, however, the plankton changed. The water 

 was from that time very rich in entomostraca, and the cilioflagellates 

 became less abundant. At the same time the mackerel appeared iu the 

 fjord. All my samples had been collected at the mouth of the fjord, 

 where the water is not very deep. In the interior the fjord becomes 

 deeper, as is the case also with the Scotch lochs, and I now wished to 

 know the character of the plankton at different depths. What I 

 hitherto had examined was the plankton of the current, called by the 

 Swedish hydrographers the Baltic current, which in the spring and 

 summer runs along the Scandinavian coast up to Bergen, in Norway. 

 Below that surface current there exists, according to the Swedish 

 hydrographers, water with lower temperature and greater salinity. In 



• Reprinted from Nature, vol. Iv. No. 1413. 



