CHAPTER X 
PROTOZOA 
INFUSORIA 
A FREE-SWIMMING CILIATE INFUSORIAN (Paramecium) 
Paramecium, often called the slipper animalcule, is one of 
the commonest of the larger infusorians. It is a minute, single- 
celled animal, being just on the limit of vision, and is almost 
universally present in standing water which contains decaying 
vegetable matter. It is easily obtained by permitting vegetable 
matter to stand in water for a week or two. In shape it is an 
elongated ellipsoid with a wide, slightly twisted, longitudinal 
groove, called the oral groove, on one side; the surface which con- 
tains the groove may be called the ventral surface, and the oppo- 
site surface, the dorsal. The animal is colorless and transparent, 
except when it contains within its body colored food particles. 
Mount a drop of water containing Paramecia and some decay- 
ing matter on a slide, using a large, thick cover-glass, and study 
the animals under a low power of the microscope. They will be 
seen swimming rapidly about, but will gradually collect about 
the decaying matter. If they do not become quiet in a few 
minutes, it is because there is too much water under the cover- 
glass, and some of it should be withdrawn with a piece of 
blotting paper. Care should be taken that the water does not 
all evaporate. 
Observe the unsymmetrical shape of the animal, and the 
difference between the anterior and the posterior ends. Notice 
the rolling over of the animal as it swims through the water; 
184 
