ON GREEN OYSTERS. 91 
Wherever they occur the green coloration occurs; where they 
are absent there is no green colour. 
The secretion-cells are engaged in the manufacture of 
granules, which probably are ultimately discharged as mucin. 
It is a matter of some physiological interest in relation to the 
mechanism of the process of secretion generally to find that 
these cells not merely manufacture a substance like mucinogen, 
but actually separate from the biood a material which entered 
it through the walls of the alimentary canal in a condition 
chemically similar to that in which it is thus separated. We 
are not in a position to say what slight chemical modifications 
the blue pigment of the Navicula or “‘ Marennin” undergoes in 
order that it may be rendered diffusible, and so enter the 
Oyster’s blood. It is possible enough that it enters the blood 
in a condition of chemical modification which renders it colour- 
less, and that it is only by the action of the secretion-cells that 
the chemical condition of the Marennin is restored in which it 
possesses a blue tint. Possibly the condition in which 
Marennin is deposited in the secretion-cells is not precisely 
identical chemically with that in which that body existed in the 
Navicula ostrearia. Possibly the Marennin retains during 
its passage through the Oyster’s body its blue colour, but is 
taken up in such small quantities by the blood as to produce 
no visible coloration of that fluid, although its accumulation in 
the secretion-cells of the gills and labial tentacles renders it 
once more perceptible to the eye. 
The fact that the Marennin is deposited in secretion-cells of 
the tegumentary epithelium of the Oyster, though it does not 
exclude a general analogy with Flourens’ madder coloration of 
bone, yet renders it necessary to draw a marked distinction 
between the latter and the greening of the Oyster’s gill, and 
to seek other analogies for the process occurring in the Oyster. 
For the deposition of the madder pigment is effected in a 
growing tissue of the skeleto-trophic group, whilst the deposit 
of the Marennin in the Oyster’s gill is connected with the 
process of secretion. 
It does not appear that there is any other instance on record 
