ON GREEN OYSTERS. vo 
ordinary seawater I have myself observed on specimens kept in 
the marine aquarium of my laboratory in University College. 
The opinion had been entertained by those who were not 
personally acquainted with the conditions of the “ greening” 
tanks that the Oyster derived its green colour from the chlo- 
rophyll of green Algee, upon fragments of which it was supposed 
to feed. M. Gaillon, however, pointed out that the green 
colour of these Algze, viz. chlorophyll, was not a sufficiently 
permanent colouring matter to effect the coloration of the 
Oyster, being liable to turn yellow with age and digestion, 
whilst he rightly pointed to the fact that the Oyster does not 
feed upon coarse particles, such as these green Alge present. 
The possibility of the green coloration of the Oyster being 
due to the passage of chlorophyll unchanged from the alimentary 
canal of the Oyster into its blood is not apparently so remote 
as M. Gaillon supposed, since it results from the recent ob- 
servations of Mr. Poulton, of Oxford (‘ Proc. Roy. Soc.,’ 1885), 
that the green colour of the blood and integument of Lepi- 
dopterous larve has such an origin. 
However this may be there can be no hesitation about accept- 
ing M. Gaillon’s conclusion, that the Navicula ostrearia is 
the cause of the greening of the Oyster. He showed most 
distinctly that the Navicula ostrearia and the green colour 
of the Oyster come and go together, that where there is no 
Navicula ostrearia there is no greening, and where there is 
Navicula ostrearia the Oysters at once become green. He 
also showed that the Navicula has a green colour en masse, and 
that there is apparently no other green substance in the tanks 
on which the Oysters could feed, and so become impregnated. 
For some reason which is not clear M. Gaillon’s observations 
and inferences did not settle the question as to the cause of the 
greening of Oysters. There was still a belief that copper had 
in some way to do with the phenomenon. Possibly this is to 
be explained by the fact that the blue-green tint assumed by 
the Oyster’s gills is very unlike the green colour of familiar 
vegetable organisms, and very closely resembles the tint of 
some copper salts, whilst the Navicula ostrearia, with its 
