94 



PROTOZOA. 



On the side of this passage there is a weak spot, the 

 potential anus, by which useless debris is passed out. The 

 cilia are so arranged as to waft food particles into the mouth 

 and down the passage. There is a large and horse- 

 shoe shaped macronucleus, and a small micronucleus. 

 Food vacuoles and contractile vacuoles are present as 

 usual. 



Sometimes a Vorticella bell jerks itself off its stalk and 



FIG. 23. Vorticella. (After BUTSCHLI.) 



1. Structure. N, Macronucleus: , micronucleus; C V, con- 

 tractile vacuole ; m, mouth ; fv, food vacuole ; v, vestibule. 



2. Encysted individual. 3. Division. 



4. Separation of a free swimming unit the result of a division. 



5. Formation of 8 minute units (ing). 



6. Conjugation of microzooid (ing) with one of normal size. 



swims about ; in other conditions it may form a temporary 

 cyst ; normally, the cilia are very active, and the movements 

 of the stalk frequent and rapid. Multiplication may take 



