1 30 - The Cell 



CILIA 



TRICHOCYSTS . 



ENDOPLASM— 

 ECTOPLASM — 



PELLICLE. 



RADIAL CANALS. 



CONTRACTILE VACUOLE, EMPTYING 

 ORAL GROOVE 



UNDULATING MEMBRANE. 



MACRONUCLEUS- 

 MICRONUCLEUS- 



GULLET. 



CONTRACTILE VACUOLE 

 FOOD VACUOLE, FORMING 



FOOD VACUOLE 



ANAL SPOT 



POSTERIOR END. 



Fig. 7-3. Paramecium, a very familiar one-celled animal. 

 Note that even a single cell can display a rather complex 

 organization. Many of the trichocysts and cilia have been 

 omitted, to simplify the drawing. Actually these structures 

 are uniformly distributed throughout the whole surface. 



Fig. 7-4. Living paramecia, photographed at a 

 magnification of about 250 diameters. In the 

 posterior (broader) end of the lower specimen 

 one can see several food vacuoles (grouped 

 around the contractile vacuole) and trichocysts 

 (along the posterior margin.) The upper speci- 

 men is in the act of turning and shows the 

 oriented beating of the cilia, and the oral 

 groove. (Bausch and Lomb Optical Co.) 



counterpart in digestion as it occurs in the 

 human stomach. In the human stomach food 

 is subjected to the action of an acid gastric 

 juice, which contains a very active protease, 

 pepsin. Probably pepsin, or a pepsinlike pro- 

 tease, is also present in one-celled animals, al- 

 though the specific digestive enzymes of the 

 amoeba have not been isolated, due to the 

 technical difficulties of handling such small 

 organisms. During the later stages of diges- 

 tion, the vacuolar content becomes distinctly 

 alkaline. This indicates that the later-acting 

 proteases, as well as the lipases and carbo- 

 hydrases of the amoeba, are similar to the 



well-known intestinal enzymes of higher ani- 

 mals (Table 5-1). 



Absorption. Absorption, in animals, is the 

 process by which food substances pass from 

 the digestive canity into the body proper. In 

 tact, the digestive cavity can be regarded as 

 a portion of the environment that is encom- 

 passed by the animal. While the food remains 

 in the digestive cavity, it does not subserve 

 any useful function. Accordingly, digestion 

 is merely a preliminary to absorption. 



In the amoeba, as in organisms generally, 

 diffusion and osmosis play an important role 

 in absorption. After digestion, the content of 



