74 PROTOZOOLOGY 



chophthirus, 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 refractile. 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 

 content 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 distributed without apparent 

 order, in linear series, or along the body outline. When the contrac- 

 tile vacuoles are deeply seated, there is a delicate duct which con- 

 nects the vacuole with the pore on the pellicle as in Paramecium 



Fig. 28. Diagrams showing the successive stages in the formation of 

 the contractile vacuole in Paramecium muliimicromicleatum (King) ; up- 

 per figures are side views; lower figures front views; solid lines indicate 

 permanent structures; dotted lines temporary structures, a, full diastole; 

 b-d, stages of systole; e, content of ampulla passing into injection canal; 

 f, formation of vesicles from injection canals; g, fusion of vesicles to form 

 contractile vacuole; h, full diastole. 



woodruffi, or in Ophryoscolecidae. In Balantidium, Nyctotherus, etc., 

 the contractile vacuole is formed very close to the permanent cyto- 

 pyge located at the posterior extremity, through which it empties its 

 content. 



In a number of ciliates there occur radiating or collecting canals 

 besides the main contractile vacuole. These canals radiate from the 

 central vacuole in Paramecium, Frontonia, Disematostoma, etc. But 

 when the vacuole is terminal, the collecting canals of course do not 



