in the Depths of the Sea. 439 



There is another observation (if it be true), that in general 

 certain colours prevail among animals at certain depths. This 

 is what (Ersted (Meddelelser fra den naturh. Forening i Kjoben- 

 havn, 1849,p. 57) tried to establish. He believed himself to have 

 discovered " a law which holds good among the animals that 

 inhabit the sea, viz. that they have the same colour as the light 

 tinder whose action they live." He supports this by remark- 

 ing " of the changes which light undergoes in its condition, 

 that which falls upon the water is refracted so that the several 

 coloured rays of which light is composed penetrate to unequal 

 depths down into the sea. The violet and blue rays are first 

 intercepted, next the green, and so on, the red reaching to the 

 lowest depth." " The sea in this manner," he says, " may be 

 regarded as divided into strata of colour, according to the 

 condition of light at the different depths ; and these strata will 

 follow the order of the solar spectrum, i. e. from the top down- 

 wards, from violet to red." (Ersted has endeavoured to give 

 his theory a practical form by defining six such strata or 

 regions : — 



1. The violet or blue animals' region, which occupies the sur- 

 face of the open sea, — that is, the region of pelagic or oceanic 

 animals. 



2. The earthy -coloured or spotted animals' 1 region, also be- 

 ginning at the surface of the sea, but in the neighbourhood of 

 coasts comprising the belt which lies between the highest and 

 lowest tides. 



3. TJie green animals'' region, which runs in bights where 

 the green algse grow, and extends to about 10 feet below 

 the mean surface of the sea. 



4. The yellow or brown animals 1 region, from about 10 to 

 about 50 feet below the surface. 



5. The red animals, from 50 to about 500 feet. 



6. The white animals, comprising all depths below the above. 

 (Ersted' s theory seems to be based rather on speculative 



fancy than on scientific facts ; at least, 1 never could find any 

 particular agreement between these and the regions defined 

 by him. Others have had the same difficulty ; for the theory 

 has been questioned, nay, sharply opposed, at least in respect 

 to the first of (Ersted's regions, by Bernhardt and Steenstrup 

 (/. c. p. 45) , who produced many examples of pelagic animals 

 of other colours than violet or blue. I think it superfluous to 

 add my own experience of numberless pelagic animals in the 

 Mediterranean completely agreeing with this ; I shall only re- 

 mark, in passing, that among our northern Siphonophora the red 

 colour is predominant. It is, besides, undoubted that at the 

 surface of the sea there is not violet or blue light, but white. 



