V. PARAMECIUM 



Paramecium is a widely distributed representative of a very 

 highly specialized class of Protozoa, known as the Infusoria. Va- 

 rious species of Paramecium are commonly found in fresh-water 

 puddles and ponds, in almost all regions of the world. The great 

 majority of Infusoria are free-swimming forms possessing cilia 

 which, as previously noted, furnish a very efficient method of 

 locomotion. Paramecium shows a much greater specialization of 

 the different parts of the cell than does either Amoeba or Euglena. 

 Thus, we find that within the limits of the single microscopic cell, 

 which constitutes the body of this animal, special structures are 

 provided for carrying on various essential activities, such as nutri- 

 tion, excretion, reproduction, locomotion, and defense. Parame- 

 cium, therefore, provides an excellent example of the high degree 

 of structural differentiation which may be attained in a unicellular 

 animal. 



A. Structure of Paramecium 



When a drop of water containing Paramecia is examined with 

 the naked eye, it will be found with careful observation that the 

 animals can just barely be seen as tiny, rapidly moving bodies. 

 A microscopic study shows that Paramecium, when viewed as a 

 flat surface, has somewhat the shape of a shoe sole, and on this 

 account it is often referred to as the 'slipper animalcule.' When 

 a transverse section through the animal is studied, it is found to 

 be nearly circular in outline. In swimming it will be noted, con- 

 trary to what might be expected, that the animal normally moves 

 with the more blunt end pointed forward. This end is regarded 

 as the anterior end of the body, and the opposite, more pointed 

 extremity as the posterior end. (B. f. 3.) 



Beginning at the blunt anterior end, and continuing posteriorly 

 to a point slightly back of the middle of the body, is a depression, 

 known as the peristome, which gives the animal an asymmetrical 

 appearance. It becomes deeper as it passes posteriorly, and 

 finally ends in a definite tube, the gullet, which lies quite deep in 



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