[7] CAUSE OF THE GREENING OF OYSTERS. 799 



gathered with too great an amount of impurities or with too much water, 

 which is nearly always the case when the duty of gathering them was 

 intrusted to a guard, it is not always possible to have the mixture suf- 

 ficiently concentrated or as clean as is to be desired. 



Upon returning to our lodgings we poured the water charged with 

 the diatoms into deep plates, which we placed on a table near a window. 

 The diatoms soon collected on the sides and bottom of the vessels, in a 

 greenish mucilaginous layer, the thickness and tint of which varied ac- 

 cording to the richness of the gatherings. We then placed in each plate, 

 according to the size of the latter, from three to six perfectly white- 

 fleshed oysters, which had never been in a claire, the shells of which had 

 also been previously washed and brushed clean. In similar plates, filled 

 with ordinary sea water, we placed some oysters of the same kind as the 

 others. In conducting this experiment we were of the opinion that the 

 acquisition of the green color was altogether due to a peculiar regimen. 



Twenty-six hours after the commencement of the experiment all of 

 the oysters which had remained in the water charged with diatoms 

 were deeply tinged with green ; the others had not suffered any change 

 of color. Eepeated many times the experiment always gave the same 

 result; the coloration was also more intense, or just in proportion as 

 the water was more heavily charged with the diatoms. In one of our 

 experiments an opening was made in the shell of one of the oysters so 

 that the mantle of the mollusk could be seen from without. After hav- 

 ing caused this oyster to become green we again placed it in pure sea 

 water, and after some days the coloration had entirely disappeared. It 

 reappeared when the oyster was replaced in some water containing 

 Navicula ostrearia. This experiment was finally repeated at a distance 

 from the scene of our work. White-fleshed oysters, which were sent to 

 Paris, together with a flask containing water charged with the diatoms, 

 were then fed and colored with them at the Jardin des Plantes in the 

 laboratory of M. Decaisne. 



In the course of the experiment we noticed that the oysters opened 

 and closed their valves and caused currents to be established in the sur- 

 rounding water, which were carried into the animal, together with the 

 diatoms which they held in suspension. The existence and direction of 

 these currents M^as apparent wherever the coating of diatoms was soon 

 removed, thus leaving the bottom of the disk uncovered, but the cover- 

 ing of diatoms remained on those parts of the dishes where the action 

 of the currents was not perceptible. 



Carried to the buccal ax>paratus by the cilia with which the branchise 

 are provided, the Navieulm passed into the stomachs of the mollusks, 

 where they give up their contained nutriment. The yellow chlorophyll 

 is disintegrated and digested ; the soluble pigment passes directly into 

 the blood, to which it communicates its color. It is likewise the most 

 vascular portions of the animal, such as the branchise, which are most 

 deeply colored. 



