1915} Behavior of Anopheles 233 
D. Humidity. This is the product of heat, wind and water. 
Humidity is always high on the Zone, though lowest during 
the dry season. The following table gives the Mean Relative 
Humidity for the three sections of the Zone, for a period of one 
year. Inthe region of Gatun the lowest point reached was 78%, 
from February to May, and the highest was 89%. Humidity 
is a powerful agent in the regulation of breeding periods, life 
duration, time of activity, etc. 
G. Mean RELATIVE Humipity (%) 1912-1913. 
Sep. | Oct.} Nov| Dec.| Jan.| Feb.} Mar| Apr.| May} June] July | Aug. 
Ancon (Pacific 
section)......| 91 | 93 | 92} 89} 87] 83] 78) 76 | 88] 89] 90 91 
Culebra (Central 
section)......:| 93 | 93 | 93 | 91) 891] 86] 82) 80] 91) 91] 91 94 
Colon (Atlantic 
section).......| 87 | 88] 89 | 84] 82] 78 | 78! 78] 87 | 88 | 87 89 
EE. Fogs and Cloudiness. Fogs at Gatun are not numerous 
and such as do occur are nearly all dissipated by 6:30 a. m., 
and all by 8:30 a.m. As the dry season advances, night fogs 
are fewer in number. Observations at Culebra, Canal Zone, 
where fogs are of almost daily occurrence, tend to show that 
they impede the flight of mosquitos. But at Gatun the fogs 
are all light, not common, and in no way seemed to interfere 
with the flight of mosquitos. 
The dry season is marked by a general absence of clouds, 
and such as do exist, appear usually in the afternoon. Data 
is lacking as to what bearing clouds may have upon the environ- 
ment or organism, but it appears they cannot exert a big 
influence or else it would have been noted. 
