BY A MICROSCOPIC ALGA. 213 



to the colour of its waters. Others, on the contrary, 

 describe a red shade, of a very singular character, as 

 present, and various explanations of the phenomenon 

 have been given. The differences among travellers in 

 their account of this sea may be reconciled by suppos- 

 ing their observations to have been made at different 

 seasons of the year ; for, if the colour of the water 

 depends on the presence of vegetable matter, it is highly 

 probable that it will vary in degree at different seasons. 

 That its waters are occasionally coated with a scum of 

 a red colour is certain ; and portions of it have been 

 brought home and carefully examined by several natu- 

 ralists. M. Montagne has given an elaborate account of 

 specimens which he had received, and has proved that 

 the scum is entirely made up of a very minute Alga 

 which consists of delicate threads, collected in bundles, 

 and contains rings of a red matter, within a slender 

 tube. This little plant has a structure very similar to 

 the Oscillatorice, which form green scums on stagnant 

 pools ; or perhaps it more nearly resembles the pretty 

 little fresh-water Alga, called (by the somewhat jaw- 

 breaking name of) Aphanizomenon. Minute Algse of 

 this description are by no means confined to the waters 

 of the Red Sea, but are met with in many parts of the 

 ocean, sometimes extending in broad bands for hundreds 

 of miles. Mr. Darwin, in his interesting voyage, gives 

 an account of several extraordinary bands of this de- 

 scription which he met with in the Pacific Ocean. I 

 have had the advantage of inspecting some of the 

 specimens brought home by this naturalist. They are 

 very similar to the species of the Red Sea. 



