Didinium nasutum showing the two prominent girdles of cilia in full metachronous beat. If you look at higher magnification you will see the occasional short, blunt clavate cilia. These are known to not contain central microtubules. (See Wessenberg, H. and Antipa, G. Studies on Didinium nasutum. I. Structure and ultrastructure. Protistologica 4:427-447). Also this specimen represents an early divider, and just anterior to the posterior girdle of cilia, the presumptive clevage furrow can be seen at higher magnification (See Small, E. B., Antipa, G. A. and Marszalek, D. The cytological sequence of events in the binary fission of Didinium nasutum (O. F. M.). Acta Protozool. 9:275-282). This micrograph was taken in 1968 by G. Antipa on a Cambridge Mark IIA operating at 20kV. The negative magnification is 842X. Further details are available at Wessenberg, H. and Antipa, G. 1970. Capture and ingestion of Paramecium by Didinium nasutum. J. Protozool. 17:250-270.