CHAPTER Yll 



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 and 

 allowed to stand about ten days. These animals occur abundantly 

 in any water which contains considerable decaying organic matter. 

 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 

 the heel part ; while the posterior portion, which is generally broader 

 but pointed, represents the sole portion. 



At one side is a depression, the oral groove, which passes diagonally 

 from the anterior end to about the middle of the body. It is broad 

 and shallow anteriorly but it becomes narrow and deeper as it ends 

 in a mouth, which leads to the gullet. The groove usually extends 

 obliquely from right to left in P. caudatum as the animal is viewed 

 from the oral side. Occasionally cultures are found in which the 

 majority of the individuals show the groove extending from left to 



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