418 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



ance with the microscopic life which grows upon the oyster beds and 

 swims about in the adjacent waters. From the fact that the lower forms 

 of life in fresh water often api)ear in great abundance one year, while in 

 the next, from some unexplained cause, none of the same species will be 

 found in the same situation, we may conclude that similar seasonal vari- 

 ations occur in the facies of the microscopic life of a given oyster bed 

 and its vicinity. Such yearly variations in the abundance of microscopic 

 life are probably the causes of the variable condition of the oysters taken 

 from the same beds during the same season of different years. Violent 

 or sudden changes of temperature are probably often the cause of the 

 destruction of a great amount of the minute life upon which the oyster 

 feeds. Backward and stormy seasons probably also affect the abundance 

 of the microscopic life of the sea. All of these questions have, however, 

 as yet, been scarcely touched, and, judging from the disposition of many 

 ' of our students of zoology to be content merely with a description of 

 new species and the compilation of lists, instead of also entering into 

 the life-histories, relative abundance of individuals, and the iufiuence of 

 surrounding conditions upon the forms they study, it will take some time 

 yet before we get the information so much desired. When we arrive at 

 this knowledge we will know why it is that oysters taken from a certain 

 bed are in good condition for a season or two, and then for one or more 

 years are found to be watery and of poor quality, as well as why it is 

 that the oysters of certain beds, which for years have had a high reputa- 

 tion for their fine qualities, are suddenly found to be more or less green 

 in the beard, as I have been informed is now the case with the oysters 

 of Lynn Haven Bay, Virginia. 



S])eaking of the abundance of the Navicida ostrearius Kiitzing, Mr. 

 Benjamin Gaillon, in 1820, said that they inhabit the water of the tanks 

 or " parks" in which the oysters are grown in France in such immense 

 abundance at certain periods of the year that they can only be compared 

 to the grains of dust which rise in clouds and obscure the air in dusty 

 weather. Dr. Johnston, speaking of the French oysters, says that, "in 

 order to communicate to them a green color, which, as with us [in Eng- 

 land j, enhances their value in the market and in the estimation of the 

 epicure, they are placed Tor a time in tanks or 'parks,' formed in par- 

 ticular places near high-water mark, and into which the sea can be ad- 

 mitted at pleasure by means of sluices; the water, being kept shallow 

 and left at rest, is favorable to the growth of the green Confervcc and 

 Ulvce, and with these there are generated at the same time innumerable 

 crustaceous animalcules, which serve the oysters for food and tincture 

 their flesh with the desirable hue." Without stopping to criticise the 

 statement regarding the crustaceous food of the oyster, the foregoing 

 extract gives us some hints regarding the advantages arising from the 

 cultivation of oysters in more or less stagnant water, in which, as in 

 the French parks or claires, an abundance of microscopic life would be 

 generated in consequence of a nearly uniform temperature, higher in 

 the early autumn months at least than that of the water of the open 



