(53) 
XIV.— CONCLUSIONS. 
1. Although our primary object was to study the oyster under unhealthy con- 
ditions, in order to elucidate its supposed connection with infective disease, we found it 
necessary to investigate in minute detail the histology of certain parts of the body — 
especially the gills and mantle-lobes, the alimentary canal and the liver. We give 
figures and descriptions of parts of these structures in both normal and abnormal 
conditions. 
2. We have also worked out the distribution and probable function of a minute 
muscle, which we believe to be the modified representative of the protractor pedis 
muscle of some other Molluscs. 
3. A diseased condition we found in some of our experimental oysters very soon 
brought us in contact with the vexed question of "greening" in oysters, and one of 
the first results we arrived at was that there are several distinct kinds of greenness in 
oysters. Some of these, such as the green Marennes oysters and those of some ri\'crs on 
the Essex coast, are healthy ; while others, such as some Falmouth oysters containing 
copper, and some American oysters re-bedded on our coast, and which have the pale 
green leucocytosis we described in a paper to the Royal Society, are not in a healthy 
state. 
4. Some forms of greenness {e.g., the leucocytosis) are certainly associated with 
the presence of a greatly increased amount of copper in "the oyster; while other forms 
of greenness {e.g., the Marennes) have no connection with copper, but depend upon the 
presence of a special pigment (marennin), which may possibly be associated with a 
certain amount of iron. 
5. We see no reason to think that the iron in the latter case is taken in through 
the .surface epithelium of the gills and palps, but regard it, like the rest of the iron in 
the body, as a product of ordinary digestion and absorption in the alimentary canal 
and liver. 
6. We do not find that there is any excessive amount of iron in the green 
Marennes oyster compared with the colourless oyster, nor do the green parts (gills, 
palps, &c.) of the Marennes oyster contain, either absolutely or relatively to the 
colourless parts (mantle, &c.), more iron than colourless oysters. We therefore conclude 
that there is no connection between the green colour of the " Iluitres de Marennes " 
and the iron they may contain. 
7. On the other hand, we do find by quantitative analysis that there is more copper 
in the green American oyster than in the colourless one ; and more proportionately in the 
greener parts than in those that are less green. We therefore conclude that their green 
colour is due to copper. We also find a greater quantity of iron in these green American 
oysters than in the colourless ; but this excess is, proportionately, considerably less than 
that of the copper. 
