PLANKTONIC STUDIES. 625 



subject and great liiudraiices lie, as they do, in the way of exact deter- 

 minations, the same applies especially to the deep currents. New ways 

 and means must first be found for pressing into the dark labyrinth of 

 very complicated physical transactions. Kow we can only say that 

 the bathycurreuts are of great importance for the irregular constitution 

 (lud distribution of the planliton. Since the time when, through the 

 discoveries of Murray (1375), Chierchia (1885), and Chun (1887), we 

 learned to recognize tlie existence and importance of the zonary and 

 bathybic fiiuna, aiul particularly, through Chun, the vertical migration 

 of the batliypelagic animals, tlie complicated conditions of the sub- 

 marine currents must evidently have exerted an extraordinary signifi- 

 cance for planktology. Although we have liitlierto known so little 

 about this subject, yet two points stand out clearly: First, that these 

 are of great influence up(Ui tlie local and temporal oscillations of plank- 

 tonic composition ; second, that it is an untenable illusion if Hensen 

 and Brandt believe that, by means of tlieir perfect-working vertical 

 plankton net, " a column of water whose height and base area can be 

 accurately determined h;is been completely filtered" (23, p. 515); for 

 one can never certainly know what considerable changes in tlie plank- 

 ton of this colunm of water one or more undercurrents have caused 

 during the drawing up of the vertical net. 



Nerocurrents or coast streams. — .While the halicurrents or the great 

 ocean streams are influenced in the first place by the Avinds and stand 

 in immediate connection witli the air currents of our atmosi)here, it is 

 only partly the case with the local coast currents, for here a number of 

 local causes, which are to be sought in the climatic and geographical 

 condition of the neighboring coast, work together. In the case of coasts 

 which are much indented, in archiijelagos with numerous islands, etc., 

 the study of the littoral currents ])ecomes a very complicated problem. 

 The physical and geological natural condition of the coast mountains 

 and of the beach, the number and force of the incoming rivers, the quality 

 and quantity of the coast flora, etc., are here important factors. The 

 fishermen, pilots, etc., are very well acquainted with these local coast 

 currents,, which we will briefly call nerocurrents^ and are usually to be 

 trusted in the details. Scientifically these currents sliould be studied 

 more closely in smaller part and less quantity. For planktology they are 

 of very high interest and not less important than the oceanic currents. 



Next, the above-intimated reciprocal relations of the ncritic and oceanic 

 planlcton are to be taken into consideration. He who for a long time 

 has carried on the pelagic fishery at a definite point on the coast 

 knows how very much the result of this is influenced by the natural 

 condition of the coast, by the course and the extent of the coast cur- 

 rents. Straits like those of Messina and Gibraltar, harbors like those 

 of Villafranca and Portofino, furnish uncommonly rich plankton results, 

 because in consequence of the littoral currents a mass of swimming 

 animals and plants are collected together in a limited space. The vol- 

 H. Mis. 113 10 



