PLANKTONIC STUDIES. 623 



water in two adjacent regions is remarkably different and often sliarj)ly 

 contrasted, so also is tlie constitution of th\^ir 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 liydromedusa^. appeared in greater abundance (0, i^. 833). 



This change was very remarkable when the Chcdlenger (at station 

 240, June 21, 1875) h'ft the warm 'Hjlack stream" of Japan and entered 

 the cold area of quiet water adjacent on the soutli (about 35° IST. hit., 

 153° E. long".). Great i)olymixic masses of plankton, dwellers in the 

 tirst area, were here killed by the sudden change of temperature and 

 rei)laced by the monotonic copepodan fauna of the cold halistase (10, 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. ''In the cold streams there appeared a greater mass 

 of small diatoms, noctiluca, and hydromednsa:' than in the warmer 

 streams where the richer pelagic animal world {Bafliolaria, Olobif/erina) 

 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 (0, 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 attenti<m especially to the great importance of these and the 

 great accumulation of pelagic animals in limited regions of currents. 



It is a fact, that f^onorally ou a voyage tlircngli the ocean great quantifies of indi- 

 vidiiah of one sjiccies are found pressed fof/ethcr in relative! ij small sjiaees, r.ucl this is 

 true of orgnuisms Avhich, on account of their small size, are not capable of extensive 

 movements. In addition, it is also a fact that Avhen the ship is in the midst of the 

 great oceanic currents, the pelagic fishery gives the nio^.t brilliant results (8, p. 109). 

 It is quite certain that the investigation of the distribution of the pelagic organisms can not 

 progress unless aeeompanied hy aj)arallel study of the currents, the temperature, and the 

 density of the tvater (8, pp. 109, 110). 



Even the participators in the Xational expedition of Kiel could not 

 avoid noticing the great irregularity of planktonic distribution in the 

 ocean and the importance of the oceanic currents 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- 



