Keywords: Origin of Vertebrates Fig 151.png Fig 151 ”Under Surface of Scorpion Androctonus The operculum is marked out with dots and on each side of it is seen one of the pectens 1908 The Origin of Vertebrates https //archive org/details/originofvertebra1908gask Walter Holbrook Gaskell PD-old-auto-1923 1914 Origin of Vertebrates book Androctonus |