72 PROFESSOR RAY LANKESTER. 
accidental metallic impregnation. On looking further into 
the literature of ‘‘ green Oysters,” I found that though owing 
to certain peculiar circumstances the belief that green Oysters 
owe their colour to copper still survives, both popularly and 
among physiologists, yet it has been abundantly proved that 
the greening of Oysters, which is carried out as a commercial 
process on the coast of France, has nothing whatever to do 
with copper, and is directly traceable to another and _ perfectly 
definite cause, viz. the Navicula (Vibrio) ostrearia of 
Gaillon, on which the Oyster is made to feed. 
I shall here first of all give an account of what has been 
ascertained with regard to the mode in which the “ greening” 
of Oysters is produced by the agency of Navicula ostrearia. 
I shall then relate the curious coincidences of fact and fiction 
which have given support to the belief that the greening is 
caused by copper assimilated by the Oyster from the waters in 
which it lives; and, lastly, I shall describe my own observa- 
tions on both the green-coloured Oysters and on the Navicula 
ostrearia, nese observations will be found, I think, of some 
importance as tompleting the history of the mode in which the 
Oyster acquires its green colour, and have not only an economic 
or piscicultutal, but also a physiological interest. 
I. Discovury oF THE CausE OF THE ‘‘GREENING” OF 
Oysters.—he “ green Oysters,” which are known in Paris as 
*‘huitres de,Marennes,” on account of the fact that they are 
largely brought from Marennes, on the coast of Normandy, 
are universaliy recognised as being the same species as the 
ordinary European Oyster (Ostrea edulis), differing only from 
the common Oysters in the fact that the gills and labial ten- 
tacles (and no other external part) are of a deep blue-green 
colour. In Plate, VII, fig. 10, one of these Oysters, as seen 
when the right shell is removed, is represented, the drawing 
having been made from life in the zoological laboratory ue Uni- 
versity College, London. 
In France, and some other parts of the Continent, these green- 
coloured Oysters have obtained a reputation for excellence, and 
