Microtubules in spermatozoa of childia (turbellaria, acoela) revealed by negative staining.

Many intact axial units, with attached basal plates, are found in spermatozoa of Childia groenlandica negatively stained with phosphotungstic acid. Electron micrographs show a total of nine doublet microtubules, confirming observations on sectioned material, where nine peripheral doublets, but no single central ones, occurred. Living spermatozoa move by waves progressing along a double undulating membrane.