Compound Ascidian Diazona violacea, Savigny. 235 



portion of the animal being filled, as already mentioned, With a bright 

 yellow-green oily-looking substance. 



It is possible that the action of the alcohol may be merely that of 

 precipitant, for if the dyestuff (which gives a blue solution) were dissolved in 

 this oil the resultant colour would be the green of the living organism. 



The chloroplasts, as mentioned above, appear to contain a substance the 

 solution of which in alcohol has an absorption spectrum resembling a yellow 

 chlorophyll body, but it does not follow that they only contain this com- 

 pound. Some solvent for the indigo derivative may quite possibly be 

 present in them as well. 



Now if this solvent is miscible with alcohol its removal would precipitate 

 the colour body in its solid, violet-tinted form. The alcoholic solution, 

 however, would still have a greenish tint, since some of the pigment would 

 dissolve in the alcohol-solvent solution, exactly as in the case of other 

 three-component systems, and so add its blue colour to the yellow of the 

 chlorophyll-like substance. 



Hence the presence of pigment in the alcoholic solution need not 

 necessarily imply the existence of a second colour body soluble in alcohol, and 

 this indeed is believed to be the origin of the traces found in some of the 

 alcoholic extracts examined during this investigation. It was remarked that 

 the traces of colouring matter thus obtained were insoluble in absolute 

 alcohol, a fact quite in accordance with the above view, since none of the 

 natural animal solvent would then be present. 



It must, however, be pointed out that if the green colour of these extracts 

 was due to the presence of a minute quantity of the violet pigment one would 

 expect the spectrum to exhibit an absorption band about \ — 606 and not at 

 \ = 620 fi/m. It is of course a possibility that the animal solvent may shift 

 the absorption band this amount towards the red, though this seems somewhat 

 improbable in dilute solution in alcohol. It is far more likely that the traces 

 of violet pigment found in the alcoholic extract had their origin in a disinte- 

 gration of parts of the organism during extraction from purely mechanical 

 causes. Though the production of the violet colour could thus be explained 

 when specimens are preserved in alcohol, this precipitation theory seems 

 scarcely sufficient to explain all the observed facts. According to this view 

 the gradual production of the colour as observed by Prof. Herdman in 

 living specimens must arise from its production in such quantity that it can 

 no longer be kept in solution by the solvent in the pigment cells, yet there is 

 no evidence that there is more colouring matter present under these circum- 

 stances than when an ordinary green healthy colony is placed directly in 

 alcohol. Further, it affords no explanation why the pigment is produced only 



