

r^m*^: 





NOTE: (A) Scanning electron micrograph of vertical fracture surface showing 

 gradation of nacreous tablets into fine-grained structures at top and gradation 

 of prisms into nacre at bottom x2000. The most recently deposited crystals 

 are at the bottom of the micrograph. (B) Acetate peel showing similar grada- 

 tions of nacre into fine-grained structures and prisms into nacre xl25. Again, 

 the most recently deposited crystals are at the bottom of the micrograph. 



171 



