ON GREEN OYSTERS. 89 
the branchiz and the labial tentacles of the Oyster “ by a phy- 
siological process analogous to that which M. Flourens observed 
in the assimilation of madder, which gives a red coloration to 
the bones only of the animal fed upon it, whilst the cartilages, 
ligaments, and tendons remain colourless.” 
This reference to the observations of Flourens is not original 
on the part of Valenciennes, but was already made by Gaillon 
(‘ Linn. Soc. Calvados,’ 1824), who, more correctly than Valen- 
ciennes, carried out completely the analogy to the case of the 
action of madder on bone by assigning the origin of the pigment 
in the case of the Oyster to a substance taken into the alimentary 
canal as food, viz. to the Navicula ostrearia. 
We have already seen that there is abundant proof of the 
truth of Gaillon’s view, that the pigment of the green Oyster’s 
gill is derived from (or practically is) the pigment of the 
Navicula ostrearia on which it feeds, and that Valenciennes’ 
theory as to bile is gratuitous, whilst the copper theory rests 
on popular fancy and the excusable mystification of Bizio, who 
never saw a green Oyster, but discovered the copper of 
hemocyanin. 
It now remains for us to examine how far the suggestion as 
to an analogy between the localisation of the ingested pigment 
in the case of the green Oyster and in the case of the madder- 
fed pigs of Flourens is justified. 
A microscopic study of the green-coloured gills and labial 
tentacles of the Marennes Oyster establishes the fact that, so far 
from “ presenting nothing remarkable” in its distribution, the 
green pigment is localised on the surface of these organs in cer- 
tain peculiar cells of the superficial epithelium. These cells 
are large subspherical ‘secretion cells,” which are placed at 
intervals among the smaller columnar cells which constitute 
the bulk of the epithelial clothing of the gills and of the labial 
tentacles. 
The green colour is concentrated in these secretion cells, and 
is localised in the granules which they contain (Plate VII, 
fig. 14). The adoral face of the labial tentacles, when examined 
with a low power of the microscope, presents a dotted appear- 
