180 



ZOOLOGY 



one end is slightly pointed. This is called the anterior end. Do the animals 

 always move at the same rate of speed? Do they ever turn over, or is one 

 side always uppermost? What happens when they meet an obstruction? 



The locomotion of the paramoecium is caused by the movement of a 

 number of tiny threads of protoplasm, the cilia. These cilia lash the w'ater 



like a multitude of tiny oars. If a little powdered 

 carmine is allowed to run under the cover glass, the 

 currents of water caused by the cilia may easily be 

 seen. 



Some of the carmine grains may be found later 

 inside the body of the paramoecium. Notice carefully 

 the direction taken by the currents of w^ater bearing 

 the carmine grains (or food particles), and try to 

 locate a funnel-like opening. At the bottom of this 

 funnel is the mouth. 



You will notice that the particles of carmine (or 

 food materials) are gathered into little balls within the 

 almost transparent protoplasm of the cell. These 

 masses of food seem to be inclosed within a little area, 

 containing fluid, called a vacuole. Other vacuoles ap- 

 pear to be clear; these are spaces in which food has 

 been digested. One or tw^o other larger vacuoles may 

 sometimes be found, these are the contractile vacuoles; 

 their purpose seems to be to pass off waste material 

 from the cell body. This is done by pulsation of the 

 vacuole, which ultimately bursts, passing out fluid waste 

 to the outside. Solid w'astes are passed out of the cell 

 in somewhat the same manner. The nucleus of the 

 cell is not visiole in living specimens. In a cell that 

 has been stained it has been found to be a double 

 structure, consisting of one large and one small portion. 

 Make a drawing of a paramoecium, showing as many 

 of the above-mentioned parts as you can find. 



Paramoecium. Greatly 

 magnified. From 

 side. F.V., food 

 vacuole; C.V., con- 

 tractile vacuole; M, 

 mouth; N , nucleus; 

 W F., water vacuole. 

 (After Sedgwick and 

 Wilson.) 



Response to Stimuli. — In the paramoecium, as in the one-celled 

 plants, the protoplasm composing the cell can do certain things. 

 Protoplasm responds, in both plants and animals, to certain agen- 

 cies acting upon it, coming from without; these agencies we call 

 stimuli. Such stimuli may be light, differences of temperature, 

 presence of food, electricity, or other factors of its surroundings. 

 Plant and animal cells may react differently to the same stimuli. 

 In general, however, we know that protoplasm is irritable by some 

 of these factors. To severe stimuli, protoplasm usually responds 

 by contracting, another power which it possesses. We know, too, 

 that plant and animal cells take in food and change the food to 

 protoplasm, that they breathe, that they may waste away and 

 repair themselves, and that new plant and animal cells are repro- 

 duced from the original bit of protoplasm, a single cell. 



