:;iO DISCOLOURED SEA. 



causes. On the coast of Chile, a few leagues north 

 of Concepcion, the Beagle one day passed through 

 great bands of muddy water, exactly like that of a 

 swollen river; and again, a degree south of Valpa- 

 raiso, when fifty miles from the land, the same ap- 

 pearance was still more extensive. Some of the 

 water placed in a glass was of a pale reddish tint ; 

 and, examined under a microscope, was seen to 

 swarm with minute animalcula darting about, and 

 often exploding. Their shape is oval, and contract- 

 ed in the middle by a ring of vibrating curved 

 cilias. It was, however, very difficult to examine 

 them with care, for almost the instant motion ceas- 

 ed, even while crossing the field of vision, their 

 bodies burst. Sometimes both ends burst at once, 

 sometimes only one, and a quantity of coarse, 

 brownish, granular matter was ejected. The ani- 

 mal an instant before bursting expanded to half 

 again its natural size ; and the explosion took place 

 about fifteen seconds after the rapid progressive 

 motion had ceased : in a few cases it was preceded 

 for a short interval by a rotatory movement on the 

 longer axis. About two minutes after any number 

 were isolated in a drop of water, they thus perished. 

 The animals move with the naiTow apex forwards, 

 by the aid of their vibratory ciliae, and generally 

 by rapid starts. They are exceedingly minute, 

 and quite invisible to the naked eye, only covering 

 a space equal to the square of the thousandth of an 

 inch. Their numbers were infinite ; for the small- 

 est drop of water which I could remove contained 

 very many. In one day we passed through two 

 spaces of water thus stained, one of which alone 

 must have extended over several square miles. 

 What incalculable numbers of these microscopical 

 animals ! The colour of the water, as seen at some 

 distance, was Hke that of a river which has flowed 



