60 



ORGANISMS OF ONE CELL 



TWCHOCY8TS 



5" CANALS 



C. A CILIATED PROTOZOON, PARAMECIUM CAUDATUM 



An infusion of vegetable or animal matter becomes the feed- 

 ing ground not only of bacteria and flagellated protozoa, but 

 also, after some considerable time, of ciliated protozoa as well. 

 From the fact that all of these organisms appear in such infu- 

 sions, the term Infusoria 

 was formerly employed to 

 designate all of them indis- 

 criminately. The bacteria 

 were first recognized as 

 having no systematic rela- 

 tion to the other forms, 

 and were separated in 

 classification from the pro- 

 tozoa found in infusions. 

 Later the flagellated forms 

 were recognized as entirely 

 different from the ciliated 

 ones and were classified 

 under the name Mastigo- 

 phora, 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, consisting of a single 

 cell which moves rapidly through the water, turning the while 

 on its long axis. The movement is brought about by the 



pSRlSTOMS 

 MOUTH AAIO GULLET 



CONTRACTILE 



FIG. 26. Diagram of structures of Para- 

 mecium caudatum from an individual about 

 f an i ncn * n length. 



