In early embryonic development of various metazoan species, germ granules are segregated into primordial germ cells. In C. elegans, asymmetric localization and segregation of the germ granules (P-granules) is established during the first cell cycle of the zygote. This paper revealed that the segregation is mediated by liquid property of P-granules, leading to the discovery of liquid-liquid phase separation that was subsequently reported in various biological processes. I will introduce and discuss how the seminal discovery was made.