File:Fertilisation-sperm-ovum.jpg

A sperm attempts to penetrate the ovum coat to fertilize it.

Originally from http://www.pdimages.com/03709.html-ssi At their page about Images and the law http://www.pdimages.com/web9.htm it says "All of the images on the "Free Images" page are copyright-free and in the public domain in the United States."