EUGLENA, AMOEBA, AND PARAMECIUM 298 



per side of the body ; it continues to move forward to the tip of the 

 pseudopodium where it dips down and is laid on the substratum 

 over which the animal is moving and becomes a part of the station- 

 ary portion. If the specimen has several pseudopodia, one or more 

 may be developing while others are receding. In the latter, the 

 flow of plasmasol is back through the centers of the pseudopodia 

 toward the main mass. Temperature and other environmental fac- 

 tors affect the rate of locomotion. 



Dillinger mounted some of the animals on the edge of a slide in 

 a groove formed by the projecting edges of two cover glasses and 

 observed their movement from side view by tilting the microscope 

 to a horizontal position. He describes their movement as a sort of 

 walking on the progressively forming pseudopodia. The new 

 pseudopodia are formed at the advancing margin of the cell. 



PARAMECIUM, OF CLASS INFUSORIA 



This animal has been the subject of much study and the victim 

 of considerable experimentation. Paramecium caudatum is probably 

 the species most commonly studied. It is easily available and is large 

 in size, ranging between 0.2 and 0.3 mm. in length. 



Characteristics and Habitat 



Paramecium is an active cigar-shaped animal, just about large 

 enough to appear as small white specks in the water. It has a 

 definite axis and permanent anterior and posterior ends, but it is 

 asymmetrical in shape. Paramecia are easily cultured by collect- 

 ing some submerged pond weeds and allowing them to stand in a 

 jar of the pond water for several days. Or some natural creek or 

 pond water may be placed in a jar with some old dry grass or cabbage 

 leaves and allowed to stand about ten days. These animals occur abun- 

 dantly in any water which contains^considerable decaying organic mat- 

 ter. They thrive in all streams, creeks, or ponds polluted by sewage. 

 They tend to congregate at the surface and particularly in contact 

 with floating objects, where they frequently form a white scum. 

 This animal is a great favorite in zoology laboratories. 



Structure 



Paramecium is sometimes described as being slipper-shaped. The 

 anterior portion, which is blunt but generally narrower, represents 



