IX THE COLOURS AND PIGMENTS OF MOLLUSCA 193 



Green Oysters 



In connection with the colours of MoUusca, we 

 may mention the vexed question of the cause of the 

 colour of Green Oysters. Prof E. R. Lankester, 

 who studied the question in 1886, described the 

 green pigment as occurring especially in amoeboid 

 cells, which he • speaks of as " crawling over the 

 surface of the gills." He found the pigment to be 

 very refractory to solvents, to be of a blue -green 

 colour, and not to contain iron or copper. As 

 a pigment of similar nature occurs in Navicula 

 ostrearia, a diatom found in the tanks in which 

 Marennes oysters occur, and used by them as food, 

 he regarded the pigment (marennin) of the green 

 oysters as a derived pigment, which was removed 

 from the gut by amoebocytes and ultimately trans- 

 ported to the gills and there eliminated. MM. 

 Chatin and Muntz in 1894 investigated the distribu- 

 tion of iron in the oysters, and found that the green 

 parts contained about twice as much iron as the 

 colourless parts, and that the amount of iron varied 

 with the intensity of the pigmentation. More 

 recently Dr. Carazzi, in reinvestigating the whole 

 subject, has come to the following conclusions. The 

 green pigment occurs in the branchial epithelium 

 and in amoebocytes included in this epithelium, but 

 not in the " gland-cells " of Lankester. It is not 

 transported by amoebocytes from the gut, is not due 

 to Navicula, but is a special product of metabolism 

 in ' the oyster, perhaps nutritive, and is a peculiar 

 organic compound containing iron. If these con 



O 



