i6 
DISCOLOURED SEA 
CHAP. 
the whole was united into a perfect little sphere, which occupied 
the position of the septum at one end of the now quite hollow 
case. The formation of the granular sphere was hastened by 
any accidental injury. I may add, that frequently a pair of 
these bodies were attached to each other, as represented above, 
cone beside cone, at that end where the septum occurs. 
I will here add a few other observations connected with the 
discoloration of the sea from organic causes. On the coast of 
Chile, a few leagues north of Concepcion, the Beagle one day 
passed through great bands of muddy water, exactly like that of 
a swollen river ; and again, a degree south of Valparaiso, when 
fifty miles from the land, the same appearance was still more 
extensive. Some of the water placed in a glass was of a pale 
reddish tint ; and, examined under a microscope, was seen to 
swarm with minute animalcula darting about, and often explod¬ 
ing. Their shape is oval, and contracted in the middle by a 
ring of vibrating curved ciliae. It was, however, very difficult to 
examine them with care, for almost the instant motion ceased, 
even while crossing the field of vision, their bodies burst. Some¬ 
times both ends burst at once, sometimes only one, and a quan¬ 
tity of coarse, brownish, granular matter was ejected. The 
animal an instant before bursting expanded to half again its 
natural size ; and the explosion took place about fifteen seconds 
after the rapid progressive motion had ceased : in a few cases 
it was preceded for a short interval by a rotatory movement on 
the longer axis. About two minutes after any number were 
isolated in a drop of water, they thus perished. The animals 
move with the narrow apex forwards, by the aid of their vibra¬ 
tory ciliae, and generally by rapid starts. They are exceed¬ 
ingly minute, and quite invisible to the naked eye, only covering 
a space equal to the square of the thousandth of an inch. 
Their numbers were infinite ; for the smallest drop of water 
which I could remove contained very many. In one day we 
passed through two spaces of water thus stained, one of which 
alone must have extended over several square miles. What 
incalculable numbers of these microscopical animals ! The 
colour of the water, as seen at some distance, was like that of 
a river which has flowed through a red clay district ; but under 
the shade of the vessel’s side it was quite as dark as chocolate. 
The line where the red and blue water joined was distinctly de- 
