1. The cell membrane of the spermatid of the grasshopper Melanoplus differentialis is shown to be composed of a double-layered membrane 10 mµ thick. Closely applied to this is an additional outer covering 25 to 35 mµ thick which has a regular geometrical pattern.
2. Models of cell membrane structure are discussed briefly. It is suggested that the pattern results from preferential adsorption of material onto a particular component of the double-layered membrane.