ON GREEN OYSTERS. 87 
coloured solution can be obtained, but this is not a solution of 
the blue pigment. 
Although thoroughly satisfactory experiments in bulk have 
not been made, there is ample ground for asserting that the 
blue pigment of N. ostrearia is similar to the green Oyster’s 
pigment in resisting solvent agents. 
Owing to the fact that neither pigment has been obtained in 
solution, there has been some difficulty in examining their 
absorption-spectra. That of the green Oyster’s gill was ex- 
amined by transmitting a powerful beam of light through 
a single gill lamella. No isolated absorption-bands were 
detected. 
Similarly a mass of the Navicula ostrearia was examined 
by means of the micro-spectroscope and no isolated absorption- 
bands were noticed. 
A more extended physico-chemical study of the pigment of 
the Navicula ostrearia is greatly to be desired ; but, so far 
as the facts are known, they favour the supposition that the 
Oyster’s blue-green pigment is identical with or derived from 
the blue pigment of the Navicula. I propose henceforward 
to speak of the blue pigment of Navicula ostrearia as 
Marennin; and I may formulate the conclusion above noted 
thus, viz. that Marennin derived from Navicula ostrearia 
taken as food is present either unchanged or slightly modified 
in the gills of the green Oyster, and is the cause of their 
colour. 
V. Presence or Navicuna OsTREARIA IN THE INTESTINE OF 
Green Oysters. —When Gaillon wrote, the fact that the 
Lamellibranchiate Molluscs feed to a very large extent upon 
Diatomaceze was not so familiar, as it is to-day. Gaillon at 
first considered the possibility of the Navicula entering directly 
into the Oyster’s gill filaments, and only in his second paper 
(Linnean Society of Calvados, 1824) came to the conclusion 
that the channel by which the Navicula enters the Oyster is the 
alimentary canal. 
A very simple proof of the truth of this view which forms an 
