Scanning electron micrograph showing tentacles on the head of a Hydra viridis. Epithelial cells located at the base of the tentacle are in a flat, contracted state. Cell distal to the head of the H. viridis are rounded in their relaxed state. Specimens were fixed in Aldehyde-osmium fixative 0.75% glutaraldehyde, 0.75% formaldehyde and 1.0% OsO4 prepared in 0.05M sodium cacodylate buffer. Fixative was buffered to pH 7.4-7.5. H. viridis were critical point dried and sputter coated with gold. Images were taken on a FEI Quanta 200 ESEM scanning electron micrograph. This sample was photographed as a montage at a magnification of 529x and an accelerating voltage of 15kV with a 11.1 mm working distance.