140 General Biology 



body, while six to ten radiating canals communicate with these vacuoles 

 and other portions of the body. These canals collect the fluid from the 

 surrounding protoplasm and pour it into the vacuoles, after which the 

 vacuoles contract alternatively at intervals of about twenty seconds at 

 ordinary temperature and discharge their contents to the outside of the 

 body. 



This is as it is in Amoeba, where the contractile vacuoles act as 

 organs of both excretion and respiration. Paramoecia feed on bacteria 

 and certain other types of unicellular organisms. The 

 animal moves back and forth rapidly, causing a cur- 

 rent of water to be sent down the gullet so that 

 various food particles are swept in. Along the gullet 

 is a row of cilia, fused together, forming what is called 

 an undulating membrane. As the food enters the end 

 of the gullet, a food vacuole is produced, which, as 

 soon as fully formed, separates from the gullet and is 

 swept away by the rotary streaming movement of the 

 fending itself from an endoplasm. This process is known as cyclosis 

 ?£? D%,uL Fr Tt ( .)• The digestion occurs within 



tnochysts are dis- the food vacuole, while the undigested particles are 



charged and mecban- . P *■ 



icaiiy force the ene- cast out at a definite anal spot which can only be seen 

 SegnerTTfter Mast!) when these particles are discharged. 



BEHAVIOR 



Conjugation and division of Paramoecia will be discussed in the 

 following chapter. Here only the ordinary reactions of this animal will 

 be taken up. 



While Paramoecia normally swim by means of cilia, they can, when 

 forced to, exhibit great elasticity and pass through very small openings. 

 The body goes forward, turning round and round on its long axis, 

 always toward the left as it is propelled forward. This results from the 

 fact that the cilia in the oral groove grow more rapidly and effectively 

 than elsewhere. Approximately the same effect is obtained as rowing 

 in a boat in which the oars on one side are applied much more strongly 

 than on the other. The animal would naturally swim in a circle if this 

 were the only force applied, but as it rotates on its long axis continu- 

 ally, it goes forward. This produces a spiral course. The swerving, 

 when the oral side is to the left, is to the right, and when the oral side is 

 above, the body swerves downward. When the oral side is to the right, 

 the body swerves to the left, etc. The swerving in any given direction 

 is, therefore, compensated by an equal swerving in the opposite direction. 

 The resultant is a spiral path having a straight axis. 



Paramoecium responds to stimuli negatively and positively just as 

 do other forms of unicellular animals. This animal has been particu- 

 larly well studied in the laboratory as to its reactions to various stimuli, 

 and it is interesting to note that whenever any injurious substance 01 



