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Plate xi. top. Aerial view showing pattLrn of drainage ditches in level up- 

 land meadow. Highway crosses main stream in vicinity of fish hatcheries in 

 middle distance, bottom. Aerial view of salt marsh showing in foreground 

 many water-filled holes in which mosquitoes breed. In background ditching 

 machine is installing parallel ditching system. The ditches are one hundred 

 .fifty feet apart. 



