76 PROFESSOR RAY LANKESTER. 
fine blue pigment, had not been presented to the reader’s eye 
by coloured drawings, but merely spoken of by M. Gaillon in 
his description of the oyster tanks. 
In 1841 M. Valenciennes made an examination of the green 
Oysters, confining himself to the study of the green colouring 
matter as thereseen, and ignoring the evidence brought forward 
by Gaillon as to the source whence the Oysters derive it. 
Valenciennes drew attention to the important fact that, 
besides the gill lamellz and the inner face of the labial ten- 
tacles, the liver and the intestine of the green Oyster are deeply 
coloured by green pigment; but the muscles, nerves, heart, repro- 
ductive organs, and blood are free from any such colouring. 
Though Valenciennes did not draw the inference, it is clear 
that this condition points to the colouring matter being intro- 
duced into the alimentary canal, and being slowly absorbed 
thence and deposited in the gills and labial tentacles, the ab- 
sorption taking place in such small quantity as to produce no 
discoloration of the blood. 
It is to be noted that Gaillon had not been able to satisfy 
himself altogether as to the mode in which the green colour of 
the Navicula ostrearia became transferred to the Oyster 
placed in the tank with it. He discussed the possibility of the 
Navicule penetrating the gill-filaments, and rejected it; but 
he did not offer any proof of the swallowing of the Navicule 
_ by the Oyster, nor was he able to suggest how, when swallowed, 
the Navicule could impart their colouring matter to special 
regions only of the Oyster’s body. 
In a second memoir, in the ‘ Transactions’ of the Linnean 
Society of Calvados, 1824, M. Gaillon suggested what appears 
to be the true explanation of the phenomenon, viz. that the 
Oyster’s gill-tissue selects and deposits the colouring matter 
much in the same way as does the osseous tissue of pigs fed upon 
madder select and deposit the red colouring matter of that plant. 
The observation of Valenciennes on the presence of the green 
colouring matter in the intestine and liver of the Oyster was 
therefore (though he did not know it) a confirmation of 
Gaillon’s hypothesis. 
