MORPHOLOGY 



75 



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, Disemato- 

 stoma, etc. But when the vacuole is terminal, the collecting canals 

 of course do not radiate, in which case the number of the canals 

 varies among different species: one in Spirostomum, Stentor, etc., 

 2 in Climacostomum, Eschaneustyla, etc., and several in Tillina. 

 In Peritricha, the contractile vacuole occurs near the posterior 

 region of the peristome and its contents are discharged through a 

 canal into the vestibule. 



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

 the contractile vacuole in Paramecimn rnultimicronucleata (King) ; 

 upper figures are side views; lower figures front views; solid lines indi- 

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

 diastole; b-d, stages of systole; e, contents of ampulla passing into 

 injection canal; f, formation of vesicles from injection canals; g, fusion 

 of vesicles to form contractile vacuole; h, full diastole. 



Of numerous observations concerning the operation of the con- 

 tractile vacuole, that of King (1935) on Paramecimn multimi- 

 croniicleata (Figs. 28, 29) may be quoted here. In this ciliate, there 

 are 2 to 7 contractile vacuoles which are located below the ecto- 

 plasm on the aboral side. There is a permanent pore above each 

 vacuole. Leading to the pore is a short tube-like invagination of 

 the pellicle, with inner end of which the temporary membrane of 

 the vacuole is in contact (Fig. 28, a). Each vacuole has 5-10 long 



