Earring and Myers—The Rotifers of Wisconsin. 653 
about. If the slide is to be kept for a day or more, the edges of 
the cover should be sealed with vaseline to prevent evaporation. 
For permanent mounts either glycerin or glycerin jelly may 
be used; a cement cell should be spun on the slide if glycerin 
is used as a mounting median. A very convenient and strong slip 
invented by Dr. N. A. Cobb, of the Bureau of Plant Industry, is 
made of tin with a round hole punched out of the center; the 
edges are folded over to form grooves into which a 25 millimeter 
square cover slides freely (text fig. 4). Mounting is done on the 
cover glass, which is held in place by two square pieces of card¬ 
board fitting tightly in the grooves; if necessary they can be secured 
by pinching the corners of the slip. 
F/sin fin s//p end & finished s/ide cover-yfess inpoi/pon 
Text Figure 4 
Whether glycerin or glycerin jelly is to be used as the mount¬ 
ing medium, the rotifers should first be transferred to a 10 per 
cent, solution of glycerin in distilled water and set aside in cov¬ 
ered watch glasses to keep out the dust. In a few days the water 
will have evaporated, leaving the animals in glycerin, which has 
gradually penetrated the body cavity and displaced the water; the 
change will have been so gradual that ordinarily no shrinkage 
will take place. If difficult species, such as Notommatids or 
Asplanchnids, do shrink and become too much wrinkled during 
the process, reconcentration on a drop culture slide becomes neces¬ 
sary. Place several drops of glycerin in the hollow of the slide 
and transfer the shrunken rotifer to it; add just enough water, 
drop by drop, to expand the rotifer, and slide a square cover 
