200 



Heredity and Environment 



FIGS. 70, 71, 72. THE CAUSE OF INVERSE SYMMETRY IN SNAILS. In each 

 case the right-hand column represents dextral forms, the left-hand column 

 sinistral ones. 



FIG. 70. NORMAL AND INVERSE SYMMETRY IN THE UNSEGMENTED EGG 



AND IN THE FlRST AND SECOND CLEAVAGES. 



