1 PELAGIC CONFERVA 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 b}' 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 erythraium^ with 

 that found over large spaces in the Red Sea, and whence its 

 name of Red Sea is derived.^ 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 iew 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 



^ M. Montagne, in Cotnptcs Rendtis, etc., Juillet 1S44; and Ainial. des Scienc. 

 Nat. December 1S44. 



