556 THE AMERICAN NATURALIST. [Vor. XXXV. 
sufficient water in it, even if the cell lies horizontal, as for micro- 
scopic examination. Moreover, this outflow affords a convenient 
method of removing the culture water and of renewing the 
medium at will without the loss of any Protozoa, if the cell is 
never permitted to overflow at its open end. A large number . 
of organisms may be filled into it by repeated use of the pipette. 
Another method of filling the cell is to prepare a siphon con- 
sisting of a single wetted piece of woolen yarn, one end of 
which is inserted with a needle into the opening of the U toa . 
depth of about 5 to 10 mm., the other end being put into the 
supplying Stender dish, elevated to permit the siphon to act. 
Over the single strand a continuous stream of Infusoria passes 
into the cell. These increase in numbers as the water passes 
through the U and escapes. 
When it is desired to use higher magnification without 
removing organisms from the cell an oblong cover-glass — 
eg., 22 X 44 mm.—may be substituted for the upper slide. 
Cover-glasses being too flexible, they must be braced in order to 
produce the even pressure upon the underlying thread neces- 
sary to retain small and active Infusoria. For this purpose 
slides are cut transversely into pieces about 5 mm. in width. 
At each end of the cover-glass one of these is laid across and 
a rubber band passed over it. At the open end of the U, as 
before, the ends of the slide and cover-glass must lie directly 
Opposite each other. Such preparations can be conveniently 
preserved for a long time by standing them in an inclined 
position inside a low cylindrical vessel, the open ends of the 
U-slide projecting above the vessel and the lower ends resting 
against a bottle or a beaker, somewhat smaller than the vessel, 
placed in its center to serve as a stop. 
The vessel may be filled with water to any desired depth. 
This method of preservation is applicable to organisms whose 
natural habitat is standing water. 
THE U-CELL For CIRCULATING MEDIA. 
The U-cell may also be used for a circulating medium, 4S 
shown in Fig. 2, The cells are placed in a cylindrical glass 
dish, with their lower ends resting in the angle of the dish. 
