580 Wisconsin Academy of Sciences, Arts, and Letters. 
the top of the lower framework. The tension of these 
springs is controlled by two clamps on the tube. Two small 
pieces of brass are damped onto the long tubes by screws 
just under the upper frame of the trap, and two just 
under the lower frame. At their inner ends they possess 
small pins which project up through the middle cross pieces 
of the frames and come in contact with the doors of the trap. 
The upper ends of these pins occupy shallow holes in the 
front edge of the doors when the latter are drawn back, and 
hold them open. The upper pins also have small coil-springs 
around them so that the lower door will not be released when 
the upper one is opened. The whole apparatus is suspended 
from two pieces of strong rope which are tied into eyes at 
the four corners of the upper framework. 
The trap is operated from a framework which is clamped 
to the coaming of the launch. It is lowered and raised by 
means of an iron hose reel which is clamped to the frame¬ 
work. The rope from the reel passes over a pulley in the 
end of a mast which projects out far enough to let the trap 
clear the side of the launch. 
This trap was designed for the purpose of ascertaining the 
degree of efficiency of both the hand and the power pumps 
in securing the more active swimmers among the plankton 
organisms. The opening is so large that there is relatively 
little disturbance of the column of water which passes 
through the open trap in its descent if the apparatus is low¬ 
ered carefully. In making a catch the trap is lowered slowly 
and carefully to the desired depth and a messenger is 
promptly sent down the line to close it. Then the trap is 
hauled to the surface where the water inside is strained 
through the net attached to the bottom and the material 
is concentrated in the plankton bucket, from which it is 
transferred to the preservative. In this way 45 liters of 
water are obtained in situ for the catch. The apparatus can 
be operated successfully only when the weather is perfectly 
calm and thus any unusual disturbances resulting from 
wave action are avoided. 
PUMPS. 
In making small catches for a study of the quantity and 
the vertical distribution of the plankton organisms, a small 
