Dr. Collingwood, on Microscopic Alga. 87 



■very remarkable by the sun sbining vipon the sea, when they 

 sparkled in the hght. Not at first recognising their nature, 

 I supposed they might be minute animals, and the source of 

 the luminous sparks which had shown so brilliantly at night ; 

 but, upon examination, I found them to be small bodies, 

 having the appearance, under a lens, of sheaves of fibres, 

 constituted as though bound round the middle, but loose at 

 the ends (see PL VI T, fig. a), like sheaves of corn in miniature. 

 Placing them under a microscope, they presented appear- 

 ances to be presently described, but, singularly enough, 

 having called the attention of the surgeon of the mail- 

 steamer to them, he at once exclaimed that it was just what 

 he had seen when he had placed under his microscope some 

 of the substance upon the Red Sea, which he had more than 

 once had an opportunity of observing when a red tint was 

 prevalent. 



I will first state the localities in which I have observed this 

 substance, and its general aspect, and afterw^ards describe the 

 microscopic appearances presented by it in various places. 

 I saAv no large patches or discoloration of the sea through it 

 anywhere in the Indian Ocean, either north or south of the 

 line, in a single passage across each, but, as I have just 

 stated, the first traces of it appeared to me in the North 

 Indian Ocean in March. So in the South Indian Ocean in 

 May, lat. 28° 29' S., and long. 38° E., I again observed the 

 sparkling appearance in the water, and once more found it to 

 be due to " dust," but not of the sheaf form, but in wedge- 

 shaped bundles to be presently described. 



In the Atlantic, I only once observed it, viz., in June (lat. 

 8° 28' 5" S., and long. 28° 32' W.) , when, standing on the fore- 

 castle one day, my attention was arrested by the sparkhng in 

 the water which indicated the presence of sea-dust, and pre- 

 sently after we crossed three long narrow streaks of the Alga 

 thickly accumulated upon the surface. This was the only 

 accumulation I ever observed out of the China Seas, and we 

 are thus reminded of the " bandes vertes " observed by 

 Chamisso between Teneriff and Brazil, in 1811. 



But the China Sea appears to be the home of this minute 

 vegetable. Having left Singapore behind, the appearance of 

 sea-dust became an every-day occurrence, in all its icmark- 

 able and interesting features. Nearly every day while tra- 

 versing this sea more or less of it was to be seen, sometimes a 

 mere sparkling appearance, while sometimes, and not un- 

 frequently, the sea was covered Avith a thick scum of a 

 yellowish-brown colour, like that which settles upon a stag- 

 nant pond. The sea in some places was entirely hidden by 



