By Schroeder (1980b; see also Maruyama et al., 1985) Another marker of polarity in the unfertilized egg is the sub-equatorial concentration of orange pigment in some batches of eggs of the Mediterranean sea urchin, Paracentrotus lividus, especially those obtained from villefranche in france (Boveri,1901; Horstadius,1973; Schrocder,1980a).