PLANKTONIC STUDIES. ; 623 
water in two adjacent regions is remarkably different and often sharply 
contrasted, so also is the constitution of their animal and vegetable 
world. Thus Murray observed a strong contrast between the cool green 
coast streams and the warmer deep-blue ocean water when the Challen- 
ger neared the coast of Chili, between Juan Fernandez and Valparaiso, 
and correspondingly there occurred a sudden change of pelagic fauna, 
for the oceanic globigerina disappeared and the neritic diatoms, infu- 
soria, and hydromeduse appeared in greater abundance (6, p. 833). 
This change was very remarkable when the Challenger (at station 
240, June 21, 1875) left the warm “black stream” of Japan and entered 
the cold area of quiet water adjacent on the south (about 35° N. lat., 
153° E. long.). Great polymixic masses of plankton, dwellers in the 
first area, were here killed by the sudden change of temperature and 
replaced by the monotonic copepodan fauna of the cold halistase (16, p, 
758). Also, later, on the voyage through the Japan stream, the plank- 
tonic contents of the tow net plainly showed the proximity of two dif- 
ferent currents. ‘Inthe cold streams there appeared a greater mass 
of small diatoms, noctiluca, and hydromeduse than in the warmer 
streams where the richer pelagic animal world (Radiolaria, Globigerina) 
remained the same which the Challenger observed from the Admiralty 
Islands to Japan.” Many similar cases occurred during the voyage, 
when proximity to the coast or the presence of coast currents was indi- 
cated by the contents of the tow net (6, p. 750). 
Observations upon the plankton richness of the oceanic currents, 
similar to those of Wyville Thompson and Murray on the Challenger 
(6) were made by Palumbo and Chierchia on the Vettor Pisani. The 
latter calls attention especially to the great importance of these and the 
great accumulation of pelagic animals in limited regions of currents. 
It is a fact, that generally on a voyage through the ocean great quantities of indi- 
viduals of one species are found pressed together in relatively small spaces, and this is 
true of organisms which, on account of their small size, are not capable of extensive 
movements. Jn addition, it is also a fact that when the ship is in the midst of the 
great oceanic currents, the pelagic fishery gives the most brilliant results (8, p. 109). 
Tt is quite certain that the investigation of the distribution of the pelagic organisms can not 
progress unless accompanied by a parallel study of the currents, the temperature, and the 
density of the water (8, pp. 109, 110). 
Even the participators in the National expedition of Kiel could not 
avoid noticing the great irregularity of planktonic distribution in the 
ocean and the importance of the oceanic eurrents in this respect. 
During the voyage it was noticed that in different Atlantic currents 
numerous forms appeared continually which were absent in the regions 
previously traversed: 
The conditions are much more complicated (!) than we had hitherto supposed (23, 
p. 518). 
But it is worthy of notice how Hensen, the leader of this plankton 
expedition, has noticed this abundant accumulation of pelagic organ- 
