18 



Circular 111 



pools harbor small killifish which promptly eat all wrigglers that 

 may appear. The result is that comparatively few mosquitoes 

 get on the wing. If, however, the weather is cloudy and the 

 atmospheric moisture high, the sheet water disappears very 

 slowly and an enormous brood of mosquitoes may escape. If the 





f$ 



Fig. 5. Draining the Salt- Mars h : Latest Power Ditcher and 

 its Work on the Salt-Marshes 

 A — Power Plant ; B — Plow ; C — Ditch which they cut 



covering tide is very high — so high as to bury the meadows 

 deeply — killifish penetrate everywhere, and whether the weather 

 is bright or cloudy, prevent the emergence of a large brood of 

 mosquitoes by eating up the wrigglers. 



