ix THE COLOURS AND PIGMENTS OF MOLLUSCA 193 
Green Oysters 
In connection with the colours of Mollusca, 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- 
