292 MOSQUITOES OF NORTH AMERICA 
from 3 to 32 days. The meteorological factor which most influences the larva 
out of the water is evaporation; up to 2 mm. evaporation does little harm but 
becomes injurious in proportion to its increase. Pupe dried upon filter paper 
survive up to 9 hours and 30 minutes. Advanced pupe produce imagos after 
drying of from 5 to 8 hours, and they would issue even while upon the filter 
paper. Pupe of any age produced imagos when placed upon the moist ground. 
To determine the resistance of the larvee upon moist earth 55 experiments 
with 3780 larvee were made. The practical conclusions are that the larve, after 
being so kept for three days, will develop in a normal manner. One larva, kept 
on moist soil for 14 days, under natural conditions, when returned to the water 
transformed to imago after three days; this was the greatest endurance observed 
by the experimenter. As in the previous drying experiments, the time of trans- 
formation was affected, the larve producing imagos in from 3 to 39 days. 
THE GEOGRAPHICAL DISTRIBUTION OF THE YELLOW-FEVER MOSQUITO. 
As is pointed out incidentally in the consideration of the carriage of mos- 
quitoes by conveyances, the yellow-fever mosquito, by reason of its habits, 
being a domestic species, having a fairly long life in the adult stage, and having 
the custom of hiding itself in the most ingenious ways, is particularly subject to 
carriage for long distances on board vessels, in railway trains, even packed 
securely away in baggage. It was in this way that the yellow-fever mosquito 
was carried from America to Africa, or vice versa, according to the view of the 
origin of the species which is adopted. It should be stated that in the old days 
of sailing vessels on very long voyages, it was not only quite possible for the 
yellow-fever mosquito to breed continuously in the more or less exposed water 
supply of the vessels, but undoubtedly this was a common occurrence. 
By such means this mosquito is distributed far and wide and during warm 
summers is taken often far beyond the point where it is capable of maintaining 
itself permanently. Thus there are two distributions for this insect, one in 
which it is capable of breeding continuously, and another over which it spreads 
during warm weather, to be annually exterminated by the cold, after breeding 
for a certain number of generations. Owing to its domestic habits, the mos- 
quito does not flourish except in the presence of fairly dense settlements. It can 
breed anywhere where man is congregated and the temperature is sufficiently 
high. Thus its permanent distribution is determined by the minimum tem- 
peratures and its temporary distribution by the maximum temperatures of any 
given region wherever it is sufficiently populated. 
The permanent distribution is limited in a general way by the frost line. 
Where frost does not occur, the species generally may breed permanently. We 
have shown in the discussion of the influence of temperature that the species 
does not thrive below a temperature of 80° Fahr., so that in a uniform climate 
with a temperature much below 80° the species could not continue to exist. 
Such climates, however, are rare, and in general when frost never occurs the 
general temperature is high enough to permit the species to flourish. Besides 
this, the species no doubt continues in particularly favored locations north of 
