ELEVENTH ANNUAL MEETING. 67 
equally certain, as Prof. Lewis’ tests have shown, for any such 
- quantity of a copper salt as would produce the green gills, heart 
and cysts in the mantle, such as are often observed, would, with- 
out doubt, be as fatally poisonous to the oyster as to a human 
being. The source of the green has recently been investigated 
by two French savants, MM. Puysegurand Decaisne, who found 
that when perfectly white-fleshed oysters were supplied with 
water containing an abundance ofa green microscopic plant, the 
Navicula ostrearia of Kiitzing, their flesh acquired a correspond- 
ing green tint. These investigators also found that if the oys- 
ters, which they had caused to become imbued with this vegeta- 
ble green, were placed in sea-water deprived of the microscopic 
vegetable food, the characteristic color would also disappear. 
Whether this will finally be found to be the explanation in all 
cases remains to be seen, as some recent investigations appear 
to indicate that it is possible that a green coloration of animal 
organisms may be due to one of three other causes besides the 
one described above as the source of the green color of the 
oyster. 
Patrick Geddes, in a recent number of Vature, has pointed out 
that the “list of supposed chlorophyll-containing animals, * * * 
breaks up into three categories ; first, those which do not con- 
tain chlorophyll at all, but green pigments of unknown function 
(Bonelia, /dotea, etc.,); secondly, those vegetating by their own 
intrinsic chlorophyll (Convoluta, Spongilla, Hydra) ; thirdly, those 
vegetating by proxy, if one may so speak, rearing copious alge 
in their own tissues, and profiting in every way by the vital ac- 
tivities of these.” This latter is one of the most interesting and 
important of modern biological discoveries, that living animal 
bodies may actually afford a nidus for the propagation of green 
microscopic plants, and not be injured, but rather be benefited 
thereby. The oxygen thrown off by the parasitic vegetable or- 
ganism appears to be absorbed by the tissues of the animal 
host, while the carbonic acid gas thrown off by the latter is ab- 
sorbed by the vegetable parasite, thus affording each other 
mutual help in the processes of nutrition and excretion. This 
singular association and inter-dependence of the animal host 
and vegetable guest has received the somewhat cumbrous name 
