PLANKTONIC STUDIES. . 625 
subject and great hindrances 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. Now we can only say that 
the bathycurrents are of great importance for the irregular constitution 
and distribution of the plankton. Since the time when, through the 
_ discoveries of Murray (1875), Chierchia (1885), and Chun (1887), we 
learned to recognize the existence and importance of the zonary and 
bathybic fauna, and particularly, through Chun, the vertical migration 
of the bathypelagic animals, the 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 the local and temporal oscillations of plank- 
tonic composition; second, that it is an untenable illusion if Hensen 
and Brandt believe that, by means of their perfect-working vertical 
plankton net, ‘‘a column of water whose height and base area can be 
accurately determined has been completely filtered” (23, p. 515); for 
one can never certainly kuow 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 much indented, in archipelagos with numerous islands, ete., 
the study of the littoral currents becomes 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 should be studied 
more closely in smaller part and Jess 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 neritic and oceanic 
plankton 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-—-—40 
