vary in length from .04 to .06, and even to .08 of an inch in length;
and in diameter from .006 to .008 of an inch. Near one extremity of
the cylindrical part, a green septum, formed of granular matter, and
thickest in the middle, may generally be seen. This, I believe, is the
bottom of a most delicate, colourless sac, composed of a pulpy
substance, which lines the exterior case, but does not extend within
the extreme conical points. In some specimens, small but perfect
spheres of brownish granular matter supplied the places of the septa;
and I observed the curious process by which they were produced. The
pulpy matter of the internal 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 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
vibratory ciliae, and generally by rapid starts. They are exceedingly
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