652 Wisconsin Academy of Sciences, Arts, and Letters. 
lution, containing nominally 40 per cent, formaldehyde. It is 
well to add a small amount of aqueous eosin and to decant after 
a few hours; the eosin stains the rotifers pink and has little ef¬ 
fect on wood fibres and minute trash, so that the animals are 
more readily picked out. Rotifers can be removed from vials 
without fear of loss if they are not poured out but taken out 
in the following manner: first, be sure that everything has settled 
to the bottom if the water has been previously disturbed, then 
draw off about two thirds of the water, being careful not to take 
up any rotifers; next agitate the remainder with the pipette, but 
do not blow air through it, draw all into the pipette and transfer 
to a watch glass. The vial is next filled one quarter full of water 
and gently agitated; the entire contents is then drawn into the 
pipette and added to the collection in the watch glass. From this 
the animals may be picked out under a dissecting microscope or 
binocular with a low power. 
A very convenient form of pipette is made with a brass top, 
drilled to fit a readily obtainable size of glass tubing, which is 
cemented in and drawn out at the free end to a fine point; a 
commercial test-tube cap on the brass top completes the pipette 
(text fig. 3). Its principal advantage is that it is easily repaired; 
the rubber caps are obtainable in most cities, and a broken point 
can be repaired by almost anyone. 
•-»))/)> 
Text Fig. 3.—Pipette. 
Temporary mounting of living or preserved material should be 
done on slides with concave, ground centers; the cavity ought 
not to be over 10 millimeters in diameter or small specimens will 
be hard to find, and if it is over millimeter deep the higher 
power objectives will not work through the center of the cell. 
The cover glass should never be lowered into place directly over 
the cell; place a drop of liquid at the side of the cell and lower 
the cover on this drop; then push it over the cell. Covers 18 or 
20 millimeters square are most convenient. When the slide is 
examined on an inclined instrument, the rotifers gradually sink 
to the lower edge of the cell, touching both cover and slide; they 
can then be turned into any desired position by pushing the cover 
