IX THE COLOURS AND PIGMENTS OF MOLLUSCA 191 



the pigment of LimncBa stagnalis, which he states is 

 iron-containing. Andrd regards melaine as a waste 

 product stored up in the tissues. When we consider 

 the almost universal presence of pigment in the shell 

 of shelled forms, it seems not unnatural to conclude 

 that the large amount of pigment in the ink of 

 Cephalopods is associated with the suppression of 

 the shell, which has thus, as it were, forced the 

 organism to get rid of its pigment by some new 

 means. 



The beautiful purple colouring-matter of the fluid 

 of lanthina has always attracted much attention, but 

 in this case, as in those of the chromogen of Murex 

 and the pigment of Aplysia, there have been few 

 exact investigations. The colour of the secretion 

 of Aplysia has been asserted to be due to natural 

 aniline dyes, but this, according to Krukenberg, is 

 incorrect. Moseley found it to be soluble in alcohol 

 with a purple colour, turning violet with acid ; 

 it was very unstable and gave two sets of spectra 

 according as it was or was not acidified. The pig- 

 ment of lanthina, on the other hand, dissolved in 

 alcohol to form a violet or pinkish-blue solution, 

 acid turning it a light pale blue. It gave a spectrum 

 with three bands. It would be interesting to know 

 if these curious pigments occur elsewhere in Mollusca, 

 and if they have any connection with the blue pig- 

 ments of shells like the common mussel. 



In connection with the pigments of the secretions 

 we may note the peculiar pigment enterochlorophyll, 

 which is so widely spread in the digestive glands of 

 the Mollusca. In Patella I find that it occurs in 

 the epithelial cells lining the alimentary canal, in the 



