PLANKTONIC STUDIES. . 625 



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

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

 and moans must fu'st be found for pressing into the dark labyrinth of 

 very complicated physical transactions. Xow we can only say that 

 the bathycurreuts are of great importtmce for the irregular constitution 

 and (lisfrihution of the planTcton. Since the time when, through the 

 discoveries of Murray (1875), Ohiercliia (1885), and Chun (1887), we 

 learned to recognize tlie existence and importance of the zouary and 

 bathybic fauna, and particularly, through Chun, the vertical mixjration 

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

 marine currents must evidently have exerted an extraordinary signifi- 

 cance for planktology. Although we have hitherto known so little 

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

 are of great influence upon tlie local and temporal oscillations of plank- 

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

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

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

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

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

 ton of this column 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 winds and stand 

 in immediate connection with the air currents of our atmosphere, 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 mucli indented, in archipelagos witli numerous islands, etc., 

 the study of the littoral currents becomes a very comi^licated j)roblem. 

 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 

 tishermen, pilots, et(^, are very well acquainted with these local coast 

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

 trusted in the details. Scientifically these currents should be studied 

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

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



Next, the above-intimated reciprocal relations of the neriticand oceanic 

 planMon 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 Villafrancaand Portofino, furnish uncommonly richiflankton results, 

 because in consequence of the littoral currents a mass of swinnning 

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

 H. Mis. 113 40 



