Mr. H. J. Carter on the Colouring Matter of the Red Sea. 183 



ser. 4 (Zool.) t. iii. p. 179), are the most elaborate. But to 

 Ehrenberg is due the merit of having first described (in 1826) 

 the nature of the organism from which this colouring matter is 

 derived. He found it in the Bay of Tor itself, pronounced it to 

 be an Oscillatoria, and called it Trichodesmium erythrceum, which 

 Montagne has advisedly changed to T. Ehrenbergii. 



No one who has read Montagne's memoir, and seen his 

 illustration together with the organism itself, can doubt that the 

 chief source of the red colour of the Red Sea is owing to the 

 presence of this little Oscillatoria. Nor can any one doubt, who 

 who has read M. Dareste's memoir, that this is not the only 

 organism which colours the sea red in different parts of the 

 world. 



It was to confirm the observations of the latter, as well as to 

 record the fact itself, that I wrote the paper in these ' Annals ' 

 for 1858 (vol. i. p. 258), entitled " On the Red Colouring Matter 

 of the Sea on the Shores of the Island of Bombay," wherein it 

 is shown that this colour depends on the presence of a Peridi- 

 nium (P. sanguineum, Cart.) in innumerable quantities, in which 

 the chlorophyll at first is green, then becomes yellow, and lastly 

 red, when the latter, mixing with the oil-globules generated 

 pari passu in the cell, gives rise together to greater opacity, and 

 thus reflecting more strongly, makes the presence of the Peri- 

 dinia more evident, and causes the sea in which they are contained 

 rapidly and almost suddenly to become of a vermilion or minium- 

 red colour ; after which, the Peridinium falls to the bottom and 

 thus disappears, as if this were the termination of a cycle in its 

 existence. 



It was not, however (although I had formerly spent many 

 months on the coasts of Arabia), until returning to England in 

 June 1862, on board the Peninsular and Oriental Company's 

 steamer 'Malta/ that I had an opportunity of seeing the colour 

 of the Red Sea which is produced by Trichodesmium Ehrenbergii 

 — a circumstance to which I should not have alluded, had not 

 Montagne appended to his memoir certain queries which, in 

 part, I can answer, at the same time that, with much diffidence, 

 I offer a few remarks on Montagne's generic characters of 

 this organism, which are repeated by Kiitzing in his * Species 

 Algarum/ 



Commencing, then, with a short account of my own experience 

 of Trichodesmium Ehrenbergii in the Red Sea, I would observe 

 that, on the 31st of May 1862, when approaching Aden, we 

 passed through large areas of a yellowish-brown oily-looking 

 scum on the surface of the sea, and that on the 2nd of June, 

 when off the Arabian side of the first islands sighted in the 

 lower part of the Red Sea after leaving Aden ; it again appeared, 



