242 BROWN, ON DISCOLORATION OF THE ARCTIC SEAS. 



is in some places so great that " tongues " of ice and other 

 objects cannot be seen a few feet beneath the surface. 



2. Cause of the Discoloration. — These patches of discoloured 

 w'ater are frequented by vast SAvarms of the minute animals 

 upon which the great " Kight whale " of commerce {Bulcena 

 mysticetus, Linn.) alone subsists, the other species of Cetacea 

 feeding on fishes proper, and other highly-organised tissues. 

 This fact is "well known to the whalers, and, accordingly, the 

 " black water " is eagerly sought for by them, knowing that 

 in it is found the food of their chase, and, therefore, more 

 likely the animal itself. From this knowledge, and from 

 observations made Avith the usual lucidity ^f that distin- 

 guished observer. Captain Scoresby attributed the nature of 

 the discoloration to the presence of immense numbers of 

 Medusae in the sea, and his explanation has been accej^ted by 

 all marine-physical geograjDhers ; and for more than forty 

 years his curious estimate of the numbers of individual 

 Medusae contained in a square mile of the Greenland sea has 

 become a standard feature in all popular works on zoology, 

 and a stock illustration with popular lecturers. In 1860, 

 and subsequently, Avhilst examining microscopically the 

 Avaters of the Greenland sea, I found, in common with pre- 

 vious observers, that not only were immense swarms of animal 

 life found in these discoloured patches, but that it was almost 

 solely confined to these spaces. In addition, however, I ob- 

 served that the discoloration Avas not due to this medusoid 

 life, but to the presence of immense numbers of a much more 

 minute object — a beautiful raoniliform diatom, and it is this 

 diatom AA'hich brings this paper within the ken of botanists. 

 On several cold days, or from no apparent cause, the Medusa?, 

 great and small, Avould sink, but still the Avater retained its 

 usual colour, and on examining it I invariably found it to be 

 SAvarming Avith Diatomacece — the vast prejjonderance of 

 which consisted of the diatom referred to. 



It had the appearance of a minute beaded necklace about 

 -4-i^ part of an inch in diameter, of Avhich the articulations 

 are about 14^ or 1^- times as long as broad. These articulations 

 contain a brownish-green granular matter, giA'ing the colour 

 to the Avhole plant, and again through it to the sea in which 

 it is found so abundantly. The whole diatom A'aries in 

 length, from a mere point to -pV of an inch, and appears to 

 be capable of enlarging itself indefinitely longitudinally by 

 giving off further bead-like articulations. WhercA'cr, in 

 those portions of the sea, I thrcAV OA^er the towing-net, the 

 muslin in a few minutes Avas quite broAvn Avith the presence 

 of this alga in its meshes. Again, this summer, I have had 



