surface of the
water, as it appeared under a weak lens, seemed as if covered by
chopped bits of hay, with their ends jagged. These are minute
cylindrical confervae, in bundles or rafts of from twenty to sixty
in each. Mr. Berkeley informs me that they are the same species
(Trichodesmium erythraeum) with that found over large spaces in the
Red Sea, and whence its name of Red Sea is derived. (1/8. M.
Montagne in "Comptes Rendus" etc. Juillet 1844; and "Annales des
Sciences Naturelles" December 1844.) Their numbers must be
infinite: the ship passed through 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. In almost
every long voyage some account is given of these confervae. They
appear especially common in the sea near Australia; and off Cape
Leeuwin I found an allied, but smaller and apparently different
species. Captain Cook, in his third voyage, remarks that the
sailors gave to this appearance the name of sea-sawdust.

Near Keeling Atoll, in the Indian Ocean, I observed many little
masses of confervae a few inches square, consisting of long
cylindrical threads of excessive thinness, so as to be barely
visible to the naked eye, mingled with other rather larger bodies,
finely conical at both ends. Two of these are shown in Plate 6
united together. They 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 freq