152 PHYLUM PROTOZOA 



Class: Infusoria 

 VORTICELLA 



This infusorian differs from Paramecium in being a sessile ani- 

 mal, 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 perma- 

 nently 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 toward 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 noncolonial and possesses a con- 

 tractile spiral stalk. Carchesium and Zoothamnium are colonial 

 and differ from each other in that in the former each individual 

 animal contracts independently, whereas in the latter the entire 

 colony always contracts as a unit ; in both, the colonies are large 

 and easily visible, appearing often like white mold on the object 

 of attachment. Epistylis is colonial with a noncontractile stalk. 

 These animals are all common. 



Mount a drop of water on a slide, together with some vegetable 

 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. 



Notice the partial radial symmetry of the animal ; this body 

 form is due to its sessile habit of life. Paramecium, which is a 

 rapidly moving animal, is not radially symmetrical. Can you 

 explain why a sessile organism tends to be radial ? 



Exercise 1. Draw a careful outline of the expanded animal on a large 

 scale, and another of the contracted animal, and label the parts 

 mentioned above. 



