ON GREEN OYSTERS. 83 
the gills of the Marennes Oyster. Bizio having noted that his 
putrefying Venetian Oysters turned blue, started the hypo- 
thesis that this blue colour was due to the liberation of 
ammonia in the tissues by decomposition of the proteids, the 
ammonia in its nascent condition being supposed by him to 
combine with the copper which he had truly and correctly de- 
termined as a normal constituent of ordinary Oysters. He 
(never having studied a natural green Oyster) actually pro- 
ceeded further to imagine that, just as in the decomposing 
Oyster, a blue colour is produced by the development of 
ammonia and its combination with copper, so in the “ huitres 
de Marennes,” when removed from the sea and placed in tanks, 
a similar decomposition occurs during the life of the 
Oyster, and hence the gills acquire their peculiar colour. 
Bizio’s hypothesis is entirely unjustifiable, since he did not show, 
in the first place, that the ‘‘ azure” pigment of the putrescent 
Venetian Oysters was really a compound of copper. He omitted 
to apply the simplest tests, which might have served to establish 
this preliminary fact; and it is highly probable that the blue 
colour he noted in the course of the putrefaction of the Oysters 
was either an opalescence or possibly a bacterium pigment 
due to a micro-organism which established itself in his experi- 
mental vessels during the putrefaction. 
Nevertheless we must not forget that Bizio deserves con- 
siderable credit for having discovered the presence of copper in 
the tissues of Mollusca at a time when the occurrence of 
this metal as a constituent of a living organism was a startling 
novelty. It was, indeed, for many years not accepted on 
Bizio’s authority ; and it is only recently that the careful study 
of the pigment turacin by Church from the feathers of the 
plantain bird, and of the blood-pigment hemocyanin by Fre- 
deriq, Gotch and others, have definitely satisfied physiologists 
that copper does enter into the composition of the substances 
which build up animal bodies. 
III. Ossexvations on Navicuta OstreaRia (GAILLON).— 
On two occasions I have received from the botanical laboratory 
