230 Annals Entomological Society of America [Vol. VIII, 
During the entire three months, of the 264 hourly periods 
in the morning, 196 were with north winds, 76 with northwest 
winds, and only 19 for all others. Of the same number of 
evening periods, 170 were with north winds, 72 with northwest 
and but 22 for all others. In mileage, the north winds were 
stronger than those of the northwest. 
B. Temperature. The’ Isthmus’ of Panama -les very 
near to the thermal equator. Its temperature is fairly even 
the whole year, ranging from about 95° F to 65° F, the general 
mean about 80° F. . The greatest daily range of the Gatun 
section is 10-15°, and this is about 50% of that of the Central 
and Pacific sections of the Zone. As the dry season approaches, 
the maximum and minimum (absolute) temperatures fall 
gradually, on the average.1.5° F within the three months.; A 
steady, though gradual, increase in the maximum and minimum 
temperature occurs as the dry season begins to merge into the 
wet season. In the shaded portions of the breeding area it 
often becomes cool enough at night to demand a blanket for 
cover, i. e., should one care to sleep there. During the day- 
time this same locality has a very moist heat, hard to endure. 
The great regulator of temperature is the aqueous vapor, 
(Abbot 1899) “‘as it is less permeable than dry air to the waves 
of energy from the sun and still less so to those that radiate 
from the earth. Its influence in this direction is very important 
on the Isthmus of Panama because there is only a narrow strip 
of land between two great oceans, and consequently the relative 
humidity is always very high. By combining high tempera- 
tures with this high humidity there results an excessive absolute 
amount of moisture in the atmosphere.”’ 
C. Rainfall. In humid sections of the torrid zone rainfall 
is such an important factor of the environment, that a table 
showing the annual rainfall for three years for the various 
stations of the Canal Zone is inserted. The average annual 
rainfall for Gatun for the past nine years has been 129.30 
inches, and since the rainfall for 1913 was but 112.81 inches, 
and that of the two years previous still less, it follows that 
there were years when the rainfall exceeded 130 inches. In 
1913 there were 248 rainy days at Gatun, leaving but 117 days - 
with no rain, i. e., less than four months of clear weather. 
