11. Plankton Studies. 



PURELY hydrographical studies of temperature, salinity, the flow 

 of currents &c. &c. cannot of themselves give such an insight 

 into the system of ocean currents and climate, as can be gained 

 by simultaneously investigating the development and distribution of 

 organisms, and endeavouring to find out the connection between 

 the hydrographical and biological relations. 



It has already been shown, from numerous observations, that 

 the hydrographical conditions are of the greatest importance on 

 Marine Organisms. This is best known in respect to those of the 

 bottom; and Petersen's work in the Cattegat [85], and Loebnz's 

 detailed monograph on the Bay of Quarnero [6.3], have contributed 

 important additions to the enlightenment of the bottom organisms' 

 dependence on the hydrographical conditions. 



The study of the Plankton Organisms, has only been taken 

 up of late years; and it is mainly the Swedish biologists Cleve 

 and AuEiviLLius, who together with the hydrographers Petteesson 

 and Ekman, have sought for the connection between the periods 

 of the Plankton's appearance, and the hydrographical variations. 



The above named scientists are of the opinion that the various 

 ocean territories are characterised by special organisms which 

 accompany the waters in their flow. Therefore, they assume that, 

 the origin of a current can be determined by investigating its 

 Plankton. 



In order to determine the value of such a conclusion, one must 

 be fully conversant with the distribution and conditions of life of 

 such organisms, and, therefore, before we enter more minutely into 

 the results arrived at by the Swedish scientists, we will give a 

 review of the biology of the Plankton Organisms, and especially 

 that of the Pelagic Diatoms. 



Like as is done by Hackee [90], we divide the Plankton 

 Organisms into Oceanic and Neritic groups. The Oceanic forms 

 inhabit the open sea, are entirely independent of the bot- 

 tom, and can go on propagating in their floating condition without 

 undergoing any regular phase of development. They can be driven 

 in to the coast by ocean currents, and many can continue to pro- 

 pagate there provided the conditions are favourable, in such a case 

 becoming mixed with the Neritic forms. 



The Neritijc Plankton Organisms are in some manner or other 

 dependent on the bottom; and this, in respect to the various species. 



can be conditional on very diverse causes. Thus there will be 

 found in the Neritic Plankton a quantity of larva forms of animals, 

 which in a matured state belong to the fauna of the bottom and 

 the coasts (for instance fish, echinoderms, annelids). Some others, 

 such as the medusa?, undergo established phases of youth, whilst the 

 matured individuals belong to the Plankton. 



Other Neritic Organisms can certainly live and increase unhin- 

 dered in a floating state, but experience teaches us that they, never- 

 theless, keep exclusively to the shallow waters of the coast. They 

 must, therefore, for some reason or other, be dependent on the bot- 

 tom, and its influence on the waters. This especially affects the 

 lower organisms of tlie Plankton, the Pelagic Alga;, which constitute 

 the primitive nourishment to be met with in the ocean, and most 

 of these are to be found mainly along the coast. 



In the North Atlantic, the Vegetable Plankton consists almost 

 entirely of Diatoms and Peridins. 



Both these groups of plants consist of one-celled organisms, 

 which, occasionally, may be united in a chain-like colony, in which, 

 however, each link possesses entire independence. 



Propagation occurs by a parting, or dividing of the floating 

 individuals, and continues excessively rapidly so long as the outer 

 conditions of life are favourable to the species concerned. 



But, under certain circumstances, which as yet are but little 

 known in respect to the individual species, the partition of the 

 cells ceases, and in the Neritic forms thick walled Cysts or Resting 

 Spores are formed which fall to tlie bottom. 



Tlie Cysts are best known from the Pelagic Diatoms, which we 

 therefore describe at greater length. 



The Cells of the Pelagic Diatoms are for the most j)art very 

 thin walled, the protoplasm forming a thin sack within the walls, 

 whilst the greater portion of the interior of the cell consists of a 

 large sap vacuole. On account of this construction the capacity of 

 the cell is very great in comparison to its solid substance, while 

 the specific gravity is relatively little, but little greater than that 

 of the sea water. 



In consequence of this the alga sinks but very slowly to 

 the bottom, even if it does not by its own powers, viz., by the 

 formation of gas, keep afloat. Moreover, the surface is often 

 covered with hollow hairy growths (as in Chcetoccros), or fine slimy 



