Hamster sperm fertilizing a hamster oocyte. This scanning electron micrograph shows hamster sperm fertilizing a hamster oocyte. Fertilization was performed in vivo. Sperm are shown binding to the outer surface of the zona pellucida. The sample was fixed using glutaraldehyde and osmium tetroxide, dehydrated in ethanol, critically point dried, coated with gold, and examined in a Phillips XL-30 FEG scanning electron microscope.