ANIMAL CELLS 19 



of the animals. Do they move as though they had anterior 

 and posterior ends ? Do they move in straight lines ? In 

 moving, is the same side of the body kept uppermost all 

 the time? It will be noted that the body revolves now 

 and then. The paramecium is unsymmetrical, and if it 

 did not revolve it would travel in a circle. 



Does the paramecium seem more complex than the 

 amoeba ? 



Make a drawing showing all the structures noted above. 



D. VORTICELLA. (Ordinarily this may be obtained by gath- 

 ering leaves, sticks, and pond scum from fresh-water ponds and 

 pools and allowing them to stand for a few days in a warm place. 

 Very often they may be found in the material at once. Sometimes 

 colonies of certain species may be seen with the naked eye, as a 

 whitish mold, along the surface of a leaf or stick. Jar the dish and 

 note the sudden contraction of the whole mass.) 



Mount some of the vorticellse. Note the sudden dis- 

 appearance of one and then its slow reappearance into the 

 field of the microscope. Is the animal attached to any- 

 thing? If so, how? Note the transparent sheath of this 

 stem and the solid rod within. What happens to the stem 

 when the animal contracts? Note the action of the stem 

 when the animal pushes out into the field again. When 

 the vorticella contracts what shape does the body assume ? 

 What is the shape of the body when the animal is fully 

 expanded ? What is seen around the edge of the inverted 

 bell-like body ? Do these cilia move ? Note the deep oral 

 groove, bordered by cilia that extends from the edge of the 

 bell into the body. The mouth is borne at the lower end 

 of this groove. Note the currents of water that are being 

 directed toward the oral groove by the cilia. What are 

 these currents for ? 



