( 15 ) 
VII.— CxREEN 0YSTP:RS. 
(See Plate IV.) 
The discovery of a green tinge of more or less intensity, which made its 
appearance on the mantle and other parts of the body of some of the oysters in our 
experiments, started us on a series of investigations into the minute structure of the 
green parts, and the nature and causes of greenness in general in oysters. One of the 
first conclusions we arrived at was that there are several distinct kinds of greenness in 
oysters, the confusion between which in the past has led to differences of opinion and 
unfortunate controversies. The colouration has been attributed to the most varied 
causes by different investigators. It has been localised in mantle, gills, palps, heart, 
liver, intestine, or any two, three, or all of these parts. It has been stated at various 
times to be due to copper, iron, chlorophyll, entero-chlorophyll, " bile-pigment," phyco- 
cyanine, and to the pigment of certain diatoms, and all these statements have again 
been contradicted. Probably each of them was more or less correct of the particular 
oysters or organs examined by their authors. It is unfortunate that some writers have 
given rise to considerable confusion and misapprehension by not confining their con- 
clusions to the kind of oysters they investigated. 
The green of our experimental oysters we saw at once was a very different 
matter from the rich blue-green of the healthy Marennes oj ster ; certain green Falmouth 
oysters are probably different from both ; the Roach River green oysters are merely a 
paler variety of the Marennes greenness ; and, again, there is a sickly grey-green tint 
seen in some Dutch oysters when they get into poor condition which is not exactly 
the same as any of the above. 
Most of our work has been done on the pale green American oysters relaid on 
the Lancashire Coast ; but w^e have also taken occasion to examine into the other 
varieties of greenness seen in the Marennes, the Roach River, the Falmouth, and the 
Dutch oysters. We have had Marennes and Dutch oysters sent to us direct from 
France and Holland, and one of us (VV. A. H.) has visited all the chief oyster-culture 
stations on the French and Dutch Coasts. 
I. Green Oysters of Marennes (PL IV., Fig. i).— We agree with practically all 
previous investigators in regarding these oysters as being in a healthy condition 
although green. Whether the green substance is derived from food taken in by the 
mouth, or from nutriment absorbed by the surface epithelium, there can be little doubt 
that it is a product of metabolism stored up in certain large granular cells met with 
in liver, intestine, and gills. It has been said to contain a small amount of iron and 
is entirely different in its reactions from the copper-containing green pigment we have 
met with in some other oysters. With certain modifications, we accept Lankester's 
