Seaweed sex cells. Light micrograph of a section through the female reproductive parts of serrated wrack seaweed (Fucus serratus). The rounded spaces are oogonia, areas in which the female sex cells (oospheres, red) are formed. The oospheres are released into the water, where they fuse with male sex cells (antherozoids). Serrated wrack is a brown seaweed found on rocky coasts in northern Europe. Magnification: x36 at 4x5 inch size.