1832.] PELAGIC CONFERVA AND INFUSORIA II 



quite ignorant of the nature and use of this secretion. I have heard 

 from Dr. Allan of Forres, that he has frequently found a Diodon, float- 

 ing alive and distended, in the stomach of the shark ; and that on 

 several occasions he has known it eat its way, not only through the 

 coats of the stomach, but through the sides of the monster, which has 

 thus been killed. Who would ever have imagined that a little soft fish 

 could have destroyed the great and savage shark ? 



March iStk. We sailed from Bahia. A few days afterwards, when 

 not far distant from the Abrolhos Islets, my attention 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 con- 

 fervse, 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.* 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 confervee. They appear especially common in 

 the sea near Australia ; and off Cape Leeuvvin 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 confervas 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 parts 

 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 deli- 

 cate, 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 



M. Montagne, in Contptts Rendus, etc., Juillet, 1844; and Annul, des. 

 Sftenc. Nat., Dec. 1844. 



