Page:Polar Exploration - Bruce - 1911.djvu/163

Rh and Kœttlitz, both of whom had seen it used with such success in Franz Josef Land. During the wintering of the Scotia, these traps were used extensively, several of them being put out in different depths and at varying distances from the ship. The Scotia also used these traps in a depth of 161 fathoms off Coats Land.

Mention has already been made of the use of fine silk tow-nets, which were used to get samples of diatoms and other algæ drifting about on the surface of the water. These nets, while doing their botanical scouting, also gather small marine invertebrates drifting or swimming freely on or near the surface of the sea. This "plankton" investigation forms one of the most interesting forms of Polar exploration, and the Belgica, the Gauss, and the Scotia all carried out extensive investigations in this direction in Antarctic seas with very important and interesting results. But besides using such nets on the surface, the Polar explorer uses them, like other explorers of the sea in other parts of the world, for ascertaining what creatures are drifting or swimming in intermediate depths between the surface and the bottom.

The nets used for this purpose are of various sizes and shapes, the smallest may be two inches in diameter, the largest many feet: the Prince of Monaco uses a vertical plankton