THE CELLULAR BASIS OF HEREDITY 



241 



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 



Fig. 44. Inverse Symmetry in Late Embryos and Adult Stages. 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 or- 

 gan ; 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 



VOL. lxxxv. — 17. 



