OF CONCHOLOGY. 187 



green color is due to the numerous minute particles of marine 

 plants which either themselves form the food of the oyster or 

 communicate their color to the water absorbed by it, he objects 

 that the plants which most commonly find their way into the 

 reservoirs are the Ulva compressa and the Conferva littoralis, 

 which are known to turn yellow with age, and which, if macer- 

 ated and left for several days in jars of salt or even fresh 

 water, will not communicate the least tint of green to the fluid, 

 whereas both the mouth and stomach of the oyster are totally 

 unfitted for such food as Ulv8e or Confervge, 



By the aid of the microscope, M. Gaillon discovered that the 

 little green excrescences with which the stones at the bottom of 

 the tank were constantly studded were nothing more than a 

 heap of the tiny animalcules which filled the water in myriads, 

 and which, when thus collected together in a lump, become 

 visible to the naked eye. He says that, on placing a drop of 

 the water under the microscope, he perceived thousands of 

 Vibrios sporting about with every possible kind of motion — 

 sometimes with a sudden jerk or impulsion forwards or back- 

 wards, sometimes spinning round on their own axis, like the 

 needle of a compass, sometimes standing straight upon one end, 

 or darting off with astonishing velocity at some other animal- 

 cule, and sticking one of their pointed extremities into him, as 

 if it Avere a lance. 



That the green color which makes its appearance in the 

 oyster is really due to the absorption of these living atoms, M. 

 Gaillon has expressed his firm conviction, both in the " Journal 

 de Physique," above cited, and in the " Memoirs of the Linnsean 

 Society of Calvados." He assures us that as soon as the fresh 

 water is again allowed to have free access to the reservoir, the 

 oysters gradually lose both the green hue and the altered flavor 

 which accompany it, although they are sometimes so thoroughly 

 impregnated with the green matter, that they do not quite lose 

 it even in the winter, consequently long after the disappearance 

 of the Vibrios ; there is, however, a gradual and sensible 

 diminution in the tint. It is this duration of the green color so 

 long after the animalcules have ceased to exist, says M. Gaillon, 

 which accounts for the assertion that green oysters may be 

 obtained all the year round. Those, he observes, who have 

 never witnessed the intensity of the color at certain seasons of 

 the year would probably designate as green oysters any which 

 showed the faintest remnant of that tint. According to all 

 observers, it is the region of the branchiae or gills which ex- 

 hibits this peculiarity the most strikingly. Now, M. Gaillon 

 assures us, from having examined these organs with the micro- 



