227 



The Colouring Matters in the Compound Ascidian Diazona 



violacea, Savigny. 

 By Alfred Holt, M.A., D.Sc. 



(Communicated by Prof. W. A. Herdman, F.R.S. Received May 12, — 

 Read June 18, 1914.) 



1. Experimental Observations. 



The j>resent investigation on the colouring matters of the compound 

 Ascidian Diazona. violacea, Saw (= Syntethys hebridicus, Forbes and Goodsir), 

 had its origin in an observation of Prof. W. A. Herdman while dredging in 

 the neighbourhood of the Outer Hebrides in 1912. 



Some specimens of this rare Ascidian were collected by Prof. Herdman, 

 which showed whilst alive the green tint described by Forbes and Goodsir,* 

 but on placing them in alcohol for purposes of preservation it was found 

 that after a few hours the alcohol had acquired the original green colour 

 of the Ascidian, while the organism itself had changed to violet, a shade 

 nearly complementary to that of the living animal. A description of these 

 specimens has already been published.-f 



During another expedition to the Hebrides in the summer of 1913, Prof. 

 Herdman obtained so many specimens of this organism that it was possible 

 to use some of the material for an examination into the nature of the 

 green and violet pigments, but a complete study has been impossible 

 owing to the minute quantity of pigment found in any one Ascidian 

 colony, and to the fact that no fresh and living material was at my 

 disposal. The green alcoholic solution obtained from the specimens collected 

 in 1912 had been examined, and a brief account of the results was given 

 in the above-mentioned paper in the Journal of the Linnean Society, but 

 it will be useful to begin by recapitulating them here, and also to add 

 some further information. 



The green colour of the solution was not unlike that clue to chlorophyll, 



and it exhibited well marked red dichroism. The absorption spectrum 



consisted of a broad band in the orange red, which was characterised by a 



more distinct edge towards the red than towards the yellow, and there was 



also practically complete absorption at the blue end of the spectrum. The 



band had the greatest intensity about X = 620 /x,fi, and the absorption in the 



blue and violet began at \ = 470 and continued downwards. 



Though not identical, this spectrum is not unlike that of true chlorophyll, 



* 'Roy. Soc. Edin. Trans.,' vol. 20, p. 307. 



t ' Linn. Soc. Zool. Journ.,' vol. 32, May, 1913. 



