[APPENDIX]
[I. METHODS OF COLLECTING AND PRESERVING CRUSTACEA]
It may be useful to give here a few hints as to the methods of collecting Crustacea. Of the species that live in the sea, many may be found between tide-marks by turning over stones and searching among sea-weeds and in rock crevices. A small hand-net, made by fastening a bag of coarse muslin to a stout wire ring of a few inches diameter, is useful for fishing in rock pools. Shore-collecting in this manner is most productive at spring-tides, when the deeper levels of the shore are open to exploration.
Many burrowing species are to be found by digging in the sand near low-water mark. In addition to Crabs and other large species, many minute forms, Amphipods, Cumacea, and the like, inhabit such localities. The best way of collecting these is to stir up a spadeful of the sand in a bucket of water, and, after allowing the sand to settle for a few seconds, to pour off the water through a muslin bag. After repeating the operation two or three times, the contents of the bag are washed out into a jar or dish of sea-water for examination with a lens or under the microscope.
Dredging is the most effective method of obtaining Crustacea that live in deeper water. The dredge usually employed by naturalists consists of a heavy rectangular iron frame to which is attached a strong bag-shaped net. The two longer sides of the frame are sharp-edged and bevelled outwards, so as to "bite" when the dredge is dragged along the sea-bottom. To the shorter sides are hinged a pair of arms ending in rings. The dredge-rope is made fast to one of these rings, while the other is held only by a "stopping" of yarn, which gives way if the dredge should catch on a rock, and permits it to be dragged sideways off the obstruction. The size and weight of the dredge may vary according to the depth at which it is to be used and the power available for working it. A convenient size for use with a small sailing boat at moderate depths has a frame 20 by 5 inches.
Apart from dredging, many specimens from moderately deep water may be picked out from among the "rubbish" brought up on fishermen's lines or by the trawl, and various Crustacea besides the edible species find their way into Lobster and Crab pots. The true deep-sea fauna is, for the most part, only to be reached by specially-equipped expeditions, although specimens from great depths are occasionally obtained during the operations for the repair of submarine telegraph cables.
The floating animals of the surface of the sea are to be captured by means of the tow-net. This consists of a conical bag of muslin, cheese-cloth, or, best of all, silk "bolting-cloth," attached to a galvanized iron-ring of one or two feet in diameter, and having a zinc can or a strong glass jar fixed to the narrow end. The ring is attached by three equidistant cords to the towing line, and the net is towed slowly at or near the surface of the sea. When taken on board, the contents of the can are emptied into a jar of sea-water for examination. The tow-net is best used when there is only enough way on the boat to keep the net from sinking; if towed more rapidly, delicate organisms are apt to be crushed by the pressure of the water, or the net itself may be burst. The use of unnecessarily fine nets should be avoided. A fine-meshed net may not capture a single specimen of the larger Crustacea, even though these may be swarming in the water through which it is drawn.
By weighting the tow-net it may be used at various depths to capture the floating animals of mid-water. When it is so used, however, it is impossible to tell from what depth any particular specimen may have come, since it may have been captured during the hauling in of the net. For more precise investigations in deep water, "closing tow-nets" of various types have been devised, which can be opened by a "messenger" sent down the line when the net has reached the desired depth, and closed again by another "messenger" before it is hauled in.
A simple method that has proved very successful for collecting small Crustacea living on a sandy bottom in shallow water is to employ a light tow-net with a cane ring, and with a heavy sinker attached to the towing line at a distance of a few feet in front of the net. As the sinker is dragged along the bottom, the net floats up behind it, and catches small animals stirred up by its passage.