Fig. 19. Tile collectors in place on a tidal flat at Auray, 

 France. 



Fig. 20. Arcachon, France. Oyster parks with low clay 

 walls. Water is retained in those at the right at the low 

 tide, that at the left being emptied for repairs. 



FlG. 21. Arcachon. Parks with somewhat higher walls con- 

 taining cases for the growing young. Figures from Pro- 

 fessor Bashford Dean. U. S. F. C. Bulletin. 



