78 PROFESSOR RAY LANKESTER. 
year 1841, with the exception of certain observations and argu- 
ments which have tended to support the erroneous theory that 
copper is the basis of the pigment of the Oyster. The curious 
history of this error I shall now relate. But I would first 
point out that the true history of the greening of Oysters, 
although brought to a certain degree of completeness by Gaillon 
‘and by Valenciennes, was still not fully worked out. It re- 
mained to show: (Ist) that the Oysters do swallow the 
Navicula ostrearia; (2nd) that a pigment having the pecu- 
liarities determined by Valenciennes, or from which Valen- 
ciennes’ oyster-pigment could be derived, actually occurs in 
Navicula ostrearia; (3rd) that there is some mechanism in 
the Oyster by which the pigment of the Naviculz, being taken 
into the Oyster’s alimentary canal, can be absorbed and de- 
posited in the gills and labial tantacles, and nowhere else. 
To these points my own observations have been directed, and 
I shall return to them immediately after giving a history of 
the “ copper-theory.”’ 
II. Tue Correr-THEoRY or Green Oysters.—It is well 
known to cooks and housewives that an uncleansed copper 
vessel is liable to impart a bright blueish-green colour to meat 
or vegetables which are cooked in such a vessel. The colour 
so imparted is very similar in tint to that of the “ huitres de 
Marennes,” and hence in the first instance has arisen the sug- 
gestion that the green Oysters have become impregnated by 
copper. A leg of mutton or similar material when it has 
acquired a green colour through the culinary misfortune above 
noted, exhibits a uniform distribution of the green colour. 
The addition of a solution of ammonia to a small fragment of 
the discoloured meat (even if it be only very slightly greened) 
ostrearia, which, he stated, was the cause of the green coloration of the 
Marennes Oysters. Mr. Dyer published a note on the subject in ‘ Nature,’ 
September, 1877. I have since, through M. Bornet’s kind introduction, ob- 
tained the Navicule in a living condition. M. Bornet states that thirty-six 
hours is sufficient to effect the green coloration of an Oyster, previously 
colourless, if it be placed in a dish with a quantity of living Navicula 
ostrearia. He also was the first to notice (in a letter to Mr. Dyer) that the 
Navicula is blue and not green as Gaillon had stated. 
