There is one central nucleus and usually one contractile vacuole.
"Marine Protozoa from Woods Hole" by Gary N. Calkins
From the contractile vacuole (CV) the waste matter is discharged.
"The Outline of Science, Vol. 1 (of 4)" by J. Arthur Thomson
One or more contractile vacuoles may protrude from the ectoplasm.
"Encyclopaedia Britannica, 11th Edition, Volume 13, Slice 2" by Various
Waste nitrogenous products formed within the cell when work is done are passed out by means of the contractile vacuole.
"A Civic Biology" by George William Hunter
The pore of the contractile vacuole might be described in the same terms.
"Encyclopaedia Britannica, 11th Edition, Volume 14, Slice 5" by Various
Some of these cells are unusually large, and each contains one or more contractile vacuoles.
"Elementary Zoology, Second Edition" by Vernon L. Kellogg