PARAMECIUM CAUDATUM 



59 



TfftCHOCYSTS 



5" C AH A LQ 



GASTRIC VACUO 



from the ciliated ones and were classified under the name Mas- 

 tigophora, so that finally, the term Infusoria is used today to 

 include only the ciliated forms of protozoa. Of these there is 

 a great number of different types one of which Paramecium, 

 formerly known as the 

 " slipper animalcule " com- 

 mon in every ditch pool 

 or stagnant water, may 

 serve as a type for all. 



Paramecium is an elon- 

 gated somewhat cigar- 

 shaped organism consist- 

 ing of a single cell which 



Jl .Ll. I. MtCRQNUCLEUS. 



moves rapidly through 



the water turning the while MAC RONUCLEUS 



on its long axis. The 



movement is brought 



about by the synchronous 



J . , , 



beating of the water by 

 myriads of minute cilia 

 uniformly distributed over 

 the surface in diagonal 

 lines while the rotation 

 on the long axis is due 

 partly to this arrangement 

 and to the action of cilia 

 covering an extensive 

 asymmetrical peristomial 

 area extending from the 



anterior end backward to FlG - 26 - Diagram of structures of Para- 



mecium caudatum. 



about the middle of the 



body. This peristomial area does not run in a straight line 

 from the anterior end to the center but curves from the left 

 dorsal extremity to the right, ending to the left of the middle 

 of the ventral surface at the mouth. The area deepens from 

 in front backward until at the mouth a conspicuous pocket 

 is formed (Fig. 26). The mouth is a circular opening lead- 



MOUTH AW> GULLET 



CONTRACTILE VACUOLE 



