102 The Control of Mosquitoes 



find blood sufficient to satisfy them. It appeared 

 within the limits of possibility that they might fly 

 high at night during the lulls in the wind, and not 

 be noted by people in boats on the French canal. 

 The assumption was also made that the period of 

 long flight might be of limited duration. Other 

 factors bearing on the problem and all previous 

 information obtained relating to Isthmian mos- 

 quitoes were given due consideration. We contin- 

 ued the investigation, beginning by making several 

 careful observations on the French canal lasting 

 more than twenty-four hours each before reaching 

 any partial conclusions. 



On January 20, 1913, at 4.30 p.m., two ob- 

 servers were posted on the opposite bank of the 

 French canal from the propagation area, and, facing 

 the latter, watched carefully for any indication of 

 flights. They were prepared for a twenty-four 

 hour watch, although extra night work had robbed 

 them of much sleep in the past week. For two 

 hours nothing happened. At 6.20 p.m. birds ap- 

 peared in the air, apparently catching insects. 

 They were at an elevation of thirty feet or more 

 above the water surface. A little later it was 

 noted that these birds fed at a lower elevation. 

 At 6.30 interest deepened. The birds kept on 

 feeding and then flew rapidly back and forth at six 



