Volvox are spherical colonies of green algae cells clinging to a semi-transparent hollow ball of mucilage. A single colony may consist of over 500 cells, each one with a tiny pair of whip-like tails (flagella) - and all cells undulating their flagella in unison, propelling the colony through the water. Very large colonies can exceed 1 mm in diameter and are easily visible to the naked eye. Many will be found to contain daughter cells, and sometime even grand-daughter cells in various stages of development, within the hollow interior of the globe. Here the daughter cells can be seen as green developing colonial spheres within the hollow interior of the larger white spheres. Darkfield microscopy. Mag: x15 @35mm.