THE YELLOW-FEVER MOSQUITO. 9 
hatching when reached by the water. They develop better after 
having been dry for some time. In fact, it seems that they will pre- 
serve their vitality dry for six months or even longer. Freezing does 
not destroy the fertility of the eggs. The duration of the egg stage, 
when the eggs are laid upon the water, is about two days; when 
deposited above the water they hatch promptly when submerged. 
When laid upon the surface of the water they are easily sunk by any 
disturbance, and when they sink hatching is retarded and often some 
of the eggs do not hatch, particularly if the temperature of the water 
is rather low. When submerged soon after being laid on the surface 
of the water they generally perish. 
BREEDING PLACES. 
The probabilities are that the yellow-fever mosquito originally bred 
in water in holes in trees, but it has so perfectly adapted itself to the 
human species that it has become a true domestic insect and is prac- 
tically dependent for its existence upon the conditions that surround 
human habitations. This adaptation is undoubtedly of very ancient 
development. The yellow-fever mosquito is essentially a town 
mosquito, and the larve are found ESR: 
practically exclusively in artificial 
receptacles in and about houses. 
It can be said that its larve are Be i 
never found in swamps, in pools, me. 4The yellow-fever mosquito: Ege. 
or even in temporary puddles, even Greatly enlarged. (Original.) 
~ when these are in close proximity to houses. In the Tropics the large 
earthen jars in which drinking water is kept are the most frequent 
and unfailing habitat of the larve. Rain-water barrels are abundant 
breeding places. Rain-water tanks, so universally behind the houses 
in southern cities ike New Orleans, Galveston, and Mobile, are the 
source of most abundant supphes of these mosquitoes. The larve 
are also found in sagging gutters containing rain water, in tin cans, in 
cesspools, in horse troughs, in water-closet tanks, in the drain traps 
of stationary washstands, in the urns in cemeteries, in the holy-water 
fonts in churches, in pools accumulating under the water tanks, in 
water pans in the chicken yards, and in the water receptacles of 
grindstones. 
The observations of Busck and Knab in the West Indies and Cen- 
tral America indicate that the yellow-fever mosquito breeds almost 
always in clear water and seldom in foul water. ‘These observers 
always found it in artificial receptacles, except. a few times in tree 
holes near houses, and in one case in a street gutter. In the last case 
it is probable that this larva came into the gutter by the emptying 
of some household vessel. Discarded bottles and tins about houses 
547 
