I 
PELAGIC CONFERVEE 
15 
tion was called to a reddish-brown appearance in the sea. The 
whole 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 erythrseum) with 
that found over large spaces in the Red Sea, and whence its 
name of Red Sea is derived. 1 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. I11 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 the woodcut 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 
1 M. Montagne, in Comptes Rendus , etc., Juillet 1844; and Annal. des Scienc. 
Nat. December 1844. 
