The oyster industry is the only one that has thus far been developed by planting and cultivating methods, so that it is now a great industry, employing thousands of steam, internal-combustion, and sail boats in their cultivation and collection for the market. The method employed by the largest growers is by the use of power boats which drag dredges. These are rakes with a meshed bag dragging on the bottom back of the tooth bar of the dredge to collect the oysters after they are raked or torn up from their beds. This is not a scientific method, for the reason that many of the oysters are killed by the heavy dredge being dragged over them. It is largely a hit-or-miss or grab-in-the-dark method, as it is impossible to clean up the ground in this manner. Some oyster grounds will produce from three to four thousand bushels of oysters to the acre. When dredging is started it is only necessary to drag the dredge a few feet before it is filled; then, as the oysters become thinner, the drag becomes longer. They drag in all directions across the grounds, but, as they cannot see the bottom, there are places they never hit, because the wind and currents prevent a systematic covering of the ground. [Illustration: SUBMARINE OYSTER-GATHERING VESSEL By admitting water ballast into ballast tanks the vessel is allowed to sink to the bottom with sufficient weight to afford traction to the toothed driving wheels in the central operating compartment. This compartment is open at the bottom; water is prevented from entering it by the use of compressed air. As this apartment is well lighted the oysters may readily be seen lying on the bottom the full width and length of the compartment. When the boat is given headway the oysters are automatically transferred into the cargo holds by means of a system of pipes and suction pumps to induce a flow of water which carries the oysters from the dredges.] The design of a submarine oyster-dredging vessel is such that the vessel goes down to the bottom direct and the water is forced out of the centre raking compartment so that the oysters may be seen by the operator in the control department. With only a few inches of water over them, headway is then given to the submarine and the oysters are then automatically raked up, washed, and delivered through pipes into the cargo-carrying chambers, as shown. Centrifugal pumps are constantly delivering water from the cargo compartments, which induces a flow of water through the pipes leading from the "rake pans" with sufficient velocity to carry up the oysters and deposit them into the cargo holds. In this manner the bottom may be seen, and by "tracking" back and forth over the bottom the ground may be cleaned up at one operation.