IN SITU PRESERVATION OF THE TRANSVERSE FLAGELLUM OF PERIDINIUM CINCTUM (DINOPHYCEAE) FOR SCANNING ELECTRON MICROSCOPY 1

Three‐dimensional structure of the transverse flagellum was studied by means of scanning electron microscopy (SEM) in Peridinium cinctum (O.F.M.) Ehrenberg. Several fixation and dehydration procedures were compared. Cells fixed, rapidly in 1% osmium tetroxide and critical‐point dried showed accurate preservation of structural features seen in living cells; in particular, both transverse and posterior flagella were retained in the furrows on the cell surface. Osmium‐fixed and freeze‐dried, samples were prone to cellular collapse and loss of flagella. Glutar‐aldehyde‐fixed and critical‐point dried cells showed a layer of material covering the thecal plates, most conspicuously over the girdle region; flagella were absent. Stereo‐pair micrographs illustrate the 3‐dimensional configuration of the transverse flagellum. Modifications of previous structural models are proposed.