Fertilized Oogonium of Saprolegnia

(Image from MycoAlbum CD by George Barron -  see www.mycographics.com)

The fertilized oospheres (eggs) become thick-walled oospores and are the persistent spore stage.  Oospores are eventually released by breakdown of the oogonial wall.  The antheridia have completed their function and are now empty of contents.