DISCOLORATION OF THE SEA FROM ALG. 19 
the colour of blood, and Captain Tuckey discovered that this 
results from the reflection of the red ground-soil. 
-But the essential colour of the sea undergoes much more 
frequent changes over large spaces, from enormous masses of 
minute alge, and countless hosts of small sea-worms, floating 
or swimming on its surface. 
“ A few days after leaving Bahia,” says Mr. Darwin, “ not far 
from the Abrolhos islets, the whole surface of the water, as it 
appeared under a weak lens, seemed as if covered by chipped 
bits of hay with their ends jagged. Each bundle consisted of 
from twenty to sixty filaments, divided at regular intervals by 
transverse septa, containing a brownish-green flocculent matter. 
The ship passed several bands of them, one of which was about 
ten yards wide, and, judging from the mud-like colour of the 
water, at least two and a half miles long. Similar massesof floating 
vegetable matter are a very common appearance near Australia. 
During two days preceding our arrival at the Keeling Islands, 
I saw in many parts masses of flocculent matter of a brownish 
green colour, floating in the ocean. They were from half to 
three inches square, and consisted of two kinds of microscopical 
conferve. Minute cylindrical bodies, conical at each extremity, 
were involved in large numbers in a mass of fine threads.” 
“ On the coast of Chili,” says the same author, “ a few leagues 
north of Conception, the ‘ Beagle’ one day passed through great 
bands of muddy water; and again, a degree south of Valparaiso, 
the same appearance was still more extensive. Mr. Sulivan, 
having drawn up some water in a glass, distinguished by the 
aid of a lens moving points. The water was slightly stained, as 
if by red dust, and after leaving it for sometime quiet, a cloud 
collected at the bottom. With a slightly magnifying lens, small 
hyaline points could be seen darting about with great rapidity, 
and frequently exploding. Examined with a much higher 
power, their shape was found to be oval, and contracted by a 
ring round the middle, from which line curved little sete pro- 
ceeded on all sides, and these were the organs of motion. Their 
minuteness was such that they were individually quite invisible 
to the naked eye, each covering a space equal only to the one- 
thousandth of an inch, and their number was infinite, for the 
smallest drop of water contained very many. In one day we 
passed through two spaces of water thus stained, one of which 
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