U. S. B. F.—Doc. 874. PLATE IV. 
FIG. 10—SPRAYING OIL ON ALGAL PADS TO DESTROY THEIR USEFUL- 
NESS AS HIDING PLACES FOR THE IMMATURE MOSQUITO. 
FIG. 11—SECTION OF POND SHOWING PRESENCE OF WATER LILIES. 
FIG. 12.—RUSHES GROWING IN END OF POND. THESE PLANTS RARELY 
PROVIDE PROTECTION FOR MOSQUITO LARVA. 
