188 INVERTEBRATE ZOOLOGY 
INFUSORIA 
A SESSILE CILIATE INFUSORIAN (Vortice//a) 
This infusorian differs from Paramecium in being a sessile 
animal, and in that the cilia are not equally distributed over 
all parts of the body but are confined to certain parts of it. 
Vorticella and its allies are often called bell animalcules. The 
animal consists of a bell-shaped body at the end of a long stalk 
which is permanently attached to some object in the water. 
Around the upper and wider margin of the body is a row of 
large cilia. A deep oral groove, which is also bordered by cilia, 
extends from the margin towards the center of the animal and 
bears the mouth at its inner end. 
A number of genera of bell animalcules are found in both 
fresh and salt water. Vorticella is non-colonial and possesses 
a contractile spiral stalk ; Carchesium and Zodthamnium are 
colonial and differ from each other in that in the former each 
individual animal contracts independently, while in the latter 
the entire colony always contracts as a unit; in both, the colo- 
nies are large and easily visible, appearing often like white 
mould on the object of attachment; Epistylis is colonial with 
a non-contractile stalk. 
Mount a drop of water on a slide, together with some vege- 
table or other substance to which Vorticella is attached, and 
study it under the microscope. (Any other bell animalcule will 
do equally well.) Observe the shape of the animal; tap on the 
slide with a pencil and cause it to contract; note the marginal 
cilia and the current they set up in the water; find the oral 
groove and note that the current in the water tends to sweep 
small objects into it, 
