. Fresh-water biology. Freshwater biology. METHODS OF COLLECTING AND PHOTOGRAPHING 67 to enter the box through the cyHnder of netting and are thereby saved from drowning which would ensue if they could not reach the air. They may be removed through the lid at the convenience of the collector. II. Invertebrates Invertebrates are to be collected in three situations: in the aquatic vegetation bordering the shore, in the open water, beyond this vegetation-zone, and on the bottom, so that the apparatus suitable to each of these situations may be separately considered. It is convenient to consider f
. Fresh-water biology. Freshwater biology. METHODS OF COLLECTING AND PHOTOGRAPHING 67 to enter the box through the cyHnder of netting and are thereby saved from drowning which would ensue if they could not reach the air. They may be removed through the lid at the convenience of the collector. II. Invertebrates Invertebrates are to be collected in three situations: in the aquatic vegetation bordering the shore, in the open water, beyond this vegetation-zone, and on the bottom, so that the apparatus suitable to each of these situations may be separately considered. It is convenient to consider first those methods designed for qualitative work, for finding out what organisms are present, and second those methods by which the number or quantity of organ- isms present in a unit volume of water or under a unit area of sur- face may be determined. A. Collecting in Littoral Vegetation 1. By dip nets. The dip net (Fig. 10) is here of greatest use. It consists of a conical netted bag about one foot in diameter and eighteen inches deep attached to a stout ring of brass or iron, firmly fixed to a stiff, wooden handle seven or eight feet long. The lower third of the net may often be advantageously Hned with thin, cotton cloth to retain smaller organisms. A form of this net adapted to scraping flat surfaces, such as logs, flat stones, banks, etc., is also , ... Fig. io. Two forms of dip net. For de- ShOWn (Fig. 10). it has a Serm-CirCUlar scnption see text. (From photographs ^ ° ' . by the writer.) rim and a shallow bag of canvas with a bottom of No. 6 or 8 bolting cloth. The handles used on dip nets are rake handles. The iron rings may be made by any blacksmith. The bags are sold as minnow dip nets by dealers in fishing tackle or by mail-order houses. 2. By collecting larger aquatic plants. With such nets many forms visible to the naked eye may be collected directly, or the. Please note that these images are extracted from scanned page images that may have been digitally enhanc
Size: 1687px × 1481px
Photo credit: © Central Historic Books / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, booksubjectfreshwa, bookyear1918
