FIGS. 40, 41, 42. THE CAUSE OF INVERSE SYMMETRY IN 

 SNAILS. In each case the right-hand column represents dextral 

 forms, the left-hand column sinistral ones. 



FIG. 40. NORMAL AND INVERSE SYMMETRY IN THE UN- 

 SEGMENTED EGG AND IN THE FlRST AND SECOND CLEAVAGES. 



