DELICATE ORGANISMS. 35 



timber, stones and shells, often at considerable depth. A 

 loaded three pronged hook attached to a strong line, for 

 bringing up weeds, etc., from the bottom, is a very good 

 method for discovering Polj'zoa. 



ROTIFERA. 



The following instructions have been drawn up for the use 

 of collectors in distant lands, or away from home, when an 

 examination of the living material is not possible. The 

 Rotifers are thus obtained in bulk and preserved for future 

 study. 



A. PELAGIC ROTIFERS. 



I. Collect with plankton net, or with small silk straining 

 net with bottle attached, in clear water and amongst aquatic 

 weeds until a large bottle full of the material has been 

 obtained. 



II. Transfer the material into a window tank (or large, 

 clear bottle) and allow to stand for an hour or two, and place 

 the tank so that it is illuminated obliqueh^ on one side only. 

 All floating debris and dirt will fall to the bottom and the 

 Rotifera will collect and can be seen like a cloud on the illum- 

 inated side of the vessel, mostly near the surface. Here they 

 can be picked up clean with a pipette and transferred to a 

 small tube bottle (2 to 6 c. c.) 



III. The narcotizing process is performed in this tube by 

 adding one drop of eucaine Cor cocaine) i per cent, solution 

 for every 2 c. c. of water it contains, and mixing. After five 

 minutes the same quantity of the narcotic is again added. 

 The Rotifers will continue to swim about, but gradually they 

 will fall to the bottom, so that in say fifteen minutes from the 

 beginning they can be killed and fixed. 



IV. The killing and fixing is done by adding one drop of 

 I per cent, osmic acid solution for every 4 c. c. of fluid, and 

 mixing rapidly. The tube is then allowed to stand for a 

 quarter of an hour, then the clear fluid is pipetted off, and 



