188 INVERTEBRATE ZOOLOGY 



INFUSORIA 



A SESSILE CILIATE INFUSORIAN (Vorticella) 



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 Zoothamnium 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. 



