MARINE BIOLOGICAL STATION AT PORT ERIN. 



61 



I determined to make a thorough search all around the Croulin 

 Islands, the original locality ; and after some disappointing 

 hauls, on mud, round the south and east, we came upon a 

 shell-bank (no doubt Forbes's spot) lying to the north at a 

 depth of 20 to 30 fathoms and there, as the result of several 

 days' dredging, we collected over 30 fine colonies and some 

 fragments — all green when alive and all violet now when 

 preserved in alcohol. 



This abundance of fresh material enabled us on the yacht 

 to make some observations on the living animal (see fig. 19) 



n 



Fig. 19. — Diazona violacea, when alive, the " Syntethys " of Forbes. 



and its curious changes of colour. It is a pale translucent 

 green when first taken from the sea, and then becomes of a 

 much more vivid and opaque green, then a darker blue-green, 

 and finally, after living for a few days in the bright sunlight of 

 a shallow basin on deck, becomes, round its edges, of a dull 



