BULLETIN OF THE UNITED STATES FISH COMMISSION. 19 



embryos in the ponds wliiiih are produced there, and what can we do to 

 aflord the embryos, developed and swimming about in such confined 

 waters, surfaces to which they may attach themselves and become con- 

 verted into fixed spat which can afterwards be transferred to other 

 ponds or to o])en waters f 



Our experiments at Stockton, this year, have gone far towards giving 

 us a solution of some of these questions. They have shown that, first, 

 it is possible to excavate i)onds in salt marshes where oysters will also 

 grow ; secondly, artificially fertilized spawn may be placed in such places 

 and live; thirdly, such spawn may fall as spat in such iuclosures if sur- 

 faces for its attachment are provided; fourthly, it will grow just as 

 rapidly as the spat which has grown under natural conditions in the 

 open water ; fifthly, the natural microscopical food is continually gen- 

 erated within the inclosure and consists mainly of very minute animal 

 and vegetable organisms ; sixthly, the water may be partially changed 

 within the inclosure twice a day by the rise and fall of the tide pro- 

 vided a permeable diaphragm or filter composed mainly of fine sand is 

 placed in the sluice way joining the pond to the open water of the bay 

 or sea. 



It is imperatively necessary that the water used be of the right density. 

 If it is too saline or contains too little saline matter the oysters die. A 

 specific gravity varying from 1.007 to 1.020 or 1.022 seem to represent 

 about the range of density of the waters in which the American oyster 

 will thrive. In the Chesapeake Bay the water over the great oyster 

 beds ranges mostly from 1 .012 to 1.016. In the Chincoteague the density 

 may be as great as 1.022. At Wood's Holl, Massachusetts, I have found 

 oysters growing in water having a density of 1.014G, 1.0172, and 1.018. 

 The last mentioned was about the density of the water in the pond at 

 Stockton in which we obtained spat under conditions of confinement. 



DESCRIPTION OF AN IMPROVED FORM OP DIAPHRAGM FOR OYSTER 



PONDS. 



My improved permeable diaphragm is placed horizontally within an 

 oblong trunk or box, A, Fig. 1, of the accompanying plate. The box is 

 made of inch jilanks, to which strong horizontal side pieces, a, Figs. 2 

 and 3, are secured, and to which are fastened the transverse cross-bars 

 J) b, of Figs. 1, 2, 3, and 4, upon which the permeable diai>hragm rests. 

 Fig. 1 represents the trunk A secured within a jiair of quadrangular 

 frames, F F, and partially in sectional elevation in place in the trench or 

 canal leading from the pond to the open water. Fig. 2 represents the 

 construction of the end of the trunk next the open water, and Fig. 3 

 that of the end next the pond, while Fig. 4 shows the trunk as viewed 

 from above. 



On the cross-bars 5 6, a single screen of galvanized wire cloth, W, Fig. 

 1 (galvanized after it is woven), is superimposed, having meshes say one- 

 half inch in diameter; upon the wire screen a layer of gunny cloth, C, Fig. 



