1 6 DISCOLOURED SEA chap. 



the whole was united into a perfect little sphere, which occupied 

 the position of the septum at one end of the now quite hollow 

 case. The formation of the granular sphere was hastened by 

 any accidental injury. I may add, that frequently a pair of 

 these bodies were attached to each other, as represented above, 

 cone beside cone, at that end where the septum occurs. 



I will here add a few other observations connected with the 

 discoloration of the sea from organic 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 Valparaiso, when 

 fifty miles from the land, the same appearance 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 explod- 

 ing. Their shape is oval, and contracted in the middle by a 

 ring of vibrating curved ciliae. It was, however, very difficult to 

 examine them with care, for almost the instant motion ceased, 

 even while crossing the field of vision, their bodies burst. Some- 

 times both ends burst at once, sometimes only one, and a quan- 

 tity of coarse, brownish, granular matter was ejected. The 

 animal 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 narrow apex forwards, by the aid of their vibra- 

 tory cilise, and geneially by rapid starts. They are exceed- 

 ingly 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 smallest 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 like that of 

 a river which has flowed through a red clay district ; but under 

 the shade of the vessel's side it was quite as dark as chocolate. 

 The line where the red and blue water joined was distinctly de- 



