Page:Popular Science Monthly Volume 85.djvu/245

Rh All of these correspondences between the polarity, symmetry and pattern of the egg and of the developed animal are found in the cytoplasm. It is possible that the polarity may be carried over from generation to generation through the egg cell, but the symmetry and localization

 In 1, cross hatched area is blastopore; cells shaded by lines mesoderm, other cells endoderm; the spiral twist of the snail begins in opposite directions in the two embryos. In 2 the adult organization is shown with all organs inversely symmetrical; os, olfactory organ; a, anus; L, lung; V, ventricle; K, kidney. In 3 sinistral and dextral shells of adult snails are shown.

pattern develop in the ovum before or just after maturation. In this differentiation and localization of the egg cytoplasm it is probable that