74 PROTOZOOLOGY 



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Fig. 27. Diagrams showing the contractile vacuole, the accessory 

 vacuoles and the aperture, during diastole and systole in Conchoph- 

 thirus (Kidder). 



which are variable in number, are formed in the ectoplasm and 

 the body surface bulges out above the vacuoles at diastole. 



In the Mastigophora, the contractile vacuole appears to be 

 more or less constant in position. In Phytomastigina, they are 

 usually located near the anterior region and, in Zoomastigina, 

 as a rule, in the posterior half of the body. The number of the 

 vacuoles present in an individual varies from one to several. In 

 Euglenoidina, one or more vacuoles are sometimes arranged near 

 the reservoir which opens to "cytopharynx." 



In the Ciliophora, except Protociliata, there occur one to many 

 contractile vacuoles, which seem to be located in the deepest part 

 of the ectoplasm and therefore constant in position. Directly 

 above each vacuole is found a pore in the pellicle, through which 

 the contents of the vacuole are discharged to outside. In the spe- 

 cies of Conchophthirus, Kidder (1934) observed a narrow slit in 

 the pellicle just posterior to the vacuole on the dorsal surface 

 (Fig. 27). The margin of the slit is thickened and highly refrac- 

 tile. During diastole, the slit is nearly closed and, at systole, the 

 wall of the contractile vacuole appears to break and the slit opens 

 suddenly, the vacuolar contents pouring out slowly. When there 

 is only one contractile vacuole, it is usually located either near 

 the cytopharynx or, more often, in the posterior part of the body. 

 When several to many vacuoles are present, they may be dis- 

 tributed without apparent order, in linear series, or along the body 

 outline. When the contractile vacuoles are deeply seated, there is 

 a delicate duct which connects the vacuole with the pore on the 

 pellicle as in Paramecium woodruffi or in Ophryoscolecidae. In 

 Balantidium, Nyctotherus, etc., the contractile vacuole is formed 

 very close to the permanent cytopyge located at the posterior 

 extremity, through which it empties its contents. 



