DIAZONA YIOLACEA, SAVIGNY. 277 



fluid is distinctly yellow-green. The colony when taken out of the alcohol 

 is now of a light yellowish-grey tint, but has very little colour. No violet 

 has appeared in any part. 



It seems, then, that the change from green to violet, as the result of 

 preservation in alcohol, can only be effected in the case of the living, or at 

 least unfixed, animal ; and that the specimen which has been preserved in 

 formol, although it will still give out a green colour when treated with 

 alcohol, does not become violet. 



A further new point I have nov/ to state, in connection with the colour- 

 changes of this Ascidian, is that even the living colony exposed in a vessel 

 of sea- water to bright sunlight for a few days changes its colour to a notable 

 degree, and may even develop a certain amount of violet or blue coloration 

 on the surface of the colony. The abundance of material obtained off the 

 Croulin Islands enabled me, after preserving some specimens in a tank of 

 spirit (these became violet at once), and others in a jar of 10 per cent, 

 formol (these remained green), to allow othei'S to remain alive in basins of 

 sea-water on deck under observation. 



The first change noted w^as that the green Hebridean D'lazona becomes 

 distinctly greener during the first hour or so of exposure to sunlight. When 

 brought up fresh from a depth of 20 or 30 fathoms the colony is of a 

 delicate grey-green colour and has a gelatinous translucent appearance. 

 But the green soon becomes more vivid and opaque, and the colony is then 

 more solid in appearance. The green, after the lapse of some hours^ then 

 changes gradually from a yellow-green to a still more opaque and darker 

 green, and then to a blue-green. After two or three days' exposure to lioht 

 (the sea- water in the basins was frequently renewed during these obser- 

 vations) the colour of the colony round its margins, and especially in tlie 

 upper parts of the test occupied by the ascidiozooids, became distinctly 

 bluish, bluish violet, or slate-blue, usually very much of the tint of freshl_y 

 spilt "Stephens's blue-black" ink — and in this condition it remained.. 

 Some of the colonies after a few days further captivity, were evidently 

 (lead or moribund; the others we preserved in the tank of spirit, and they 

 are now all violet in colour like the rest. 



Up to the last, however, the change in colour is only superficial, affecting' 

 at the most the outer quarter to half inch in thickness of the test. Similarly, 

 the change to violet in the case of specimens preserved in alcohol^ deep and 

 opaque though the colour may seem, affects only the surface-layer of the 

 test. Even now, after some months preservation in several changes of 

 spirit, if a colony be cut open the centre is found to be of a vivid green 

 colour ; and it is interesting to notice that that green is now permanent,, 

 even when exposed to clean alcohol. Apparently the change to violet only 

 takes place in the case of the fresh specimen taken from sea-water and 

 placed in spirit. 



