coating suddenly grouped itself into lines, some of which
assumed a form radiating from a common centre; it then
continued, with an irregular and rapid movement, to contract
itself, so that in the course of a second 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 add here 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 exploding. 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. Sometimes both
ends burst at once, sometimes only one, and a quantity 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