. Culture methods for invertebrate animals;. Invertebrates -- Cultures and culture media; Invertebrates -- Collection and preservation. Fig. ii.—The box dredge. viding additional weight and pushing the material scraped by the blade into the bag. The usual dimensions are as follows: arms, 2% feet; cross bar, 2 feet; blade, 2% feet long and 2 inches wide. For operating on rough bottoms the blade is set level or even with a slight upward incline, so the dredge will slide over the bottom. A dredge of this type may be made of any size and is very useful for general collecting. For small organisms t
. Culture methods for invertebrate animals;. Invertebrates -- Cultures and culture media; Invertebrates -- Collection and preservation. Fig. ii.—The box dredge. viding additional weight and pushing the material scraped by the blade into the bag. The usual dimensions are as follows: arms, 2% feet; cross bar, 2 feet; blade, 2% feet long and 2 inches wide. For operating on rough bottoms the blade is set level or even with a slight upward incline, so the dredge will slide over the bottom. A dredge of this type may be made of any size and is very useful for general collecting. For small organisms the bags must be made of a fine twine netting or of some other strong, coarse material of the de- sired mesh. Instead of a cutting blade the dredge may be provided with a set of teeth. This type is commonly used for dredging oysters. The box dredge. The box dredge (Fig. n) consists of a rectangular iron framework 27 x 12 inches, with two folding arms and two cutting blades, one on each side of the dredge. A bag of coarse netting is at- tached to the blades. When in operation the two arms are tied together by a piece of string and the drag line is fastened only to one arm. If the dredge is caught under rocks the string breaks and the instrument may be saved by dragging it sidewise by one arm. This small dredge is very useful for general collecting. The triangular dredge. The triangular dredge (Fig. 12) has some ad- vantages over the other types because no matter which side rests on the bottom one of the blades will cut into the ground when the instrument is dragged. To facilitate the finding of a dredge in case the drag line snaps, a tail buoy is attached with a length of rope slightly greater than the depth of the water. When the instrument is being dragged slight shocks caused by the impact of the frame with rocks or other objects are conveyed along the rope and are easily noticed by the operator holding it in his hands or only touching it. He can easily feel the change in vi
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Keywords: ., bookcentury1900, bookcollectionameri, bookcollectionbiodiversity
