NATURAL HISTORY. 51 
necessary to employ a magnifier to discover 
them. ‘The best method to collect them is to 
take up a little of the water we wish to examine 
with a ladle, and pour it into a wide-mouthed 
glass phial, and examine it with a hand micro- 
scope. As they soon attach themselves to the 
sides of the bottle, they are easily detected. In 
this way fresh portions from different waters 
‘must be successively examined, till a sufficient 
number is procured. For observation under 
the microscope they are best applied to the 
stage-glass by the feeding-pin above referred to, 
covering the surface with another plate of thin 
glass, to prevent evaporation, and to render the 
surface plane, or they may be put into an 
aquatic live-box. 
The most usual form which these animalcules 
assume is that shewn in plate 5, figures 1 
and 2. The first figure represents a full-grown 
specimen, the second the same when young. 
Taking the average length of the mature Vorti- 
cella at one-fortieth of an inch, the superficial 
amplification of the drawings will be 25,600 
times, or 160 in length. It is under the form 
of figures 1 and 2 that it exhibits those curious 
rotatory organs from which its name is derived. 
When these wheels are protruded, the breadth 
Dp 2 
