PLANKTONIC STUDIES. 623 



water iu two adjacent legious 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 oc(;urred a sudden change of pelagic fauna, 

 for the oceanic globigerina disappeared and the neritic diatoms, infu- 

 soria, and hydromedusa; appeared in greater abundance ((>, p. 833). 



This change was very remarkable Avbeu the Challenger (at station 

 240, Jniie 21, 1875) left the warm ''black stream" of Japan and entered 

 the cold area of (piiet water adjacent on the south (about 35° JST. lat., 

 153° B. long.). Great x)olymixic 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 (IG, 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 ai)peared a greater mass 

 of small diatoms, noctiluca, and hydromedusa; than in the warmer 

 streams where the richer pelagic animal world (Radiolaria, Qlohigerina) 

 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 (G, 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 Yettor Fisani. 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 fart, that generally on a voyage through the ocean great quantities of indi- 

 viduals of ove S2>cciis are found pressed to(jethcr in relaiivehj small spaces, and this is 

 true of organisms ■which, on acconut of their small size, are not capable of extensive 

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

 great oceanic currents, the pelagic iishery gives the mo.st brilliant results (8, p. 109). 

 It is quite certain that ihe investitjaiion of the distribution of the peJagie organisms can not 

 progress unless aceompanicd hy a parallel study of the currents, the temperature, and the 

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



Even the participators in the KaUonal expedition of Kiel could not 

 RA'^oid noticing the great irregularity of plaiiktonic distribution in the 

 ocean and the importance of the oceanic currents in this respect. 

 During thevoynge it was noticed that in different Atlantic currents 

 numerous forms ap})eared continually which were absent in the regions 

 previously traversed : 



Tho conditions are much more cojuplicated ( !) than wo had hitherto supposed (23, 

 p. 518). 



But it is Avortliy of .notice how ITensen, the leader of this i)lankton 

 exi)edition, has noticed this abundant accumulation of pelagic organ- 



