BREEDING PLACES 147 
survival of the species is assured. All the forms so far discussed, and to them 
belong by far the most mosquitoes in point of numbers, being dependent upon 
seasonal conditions, show a marked periodicity. This is also true of the salt- 
marsh mosquitoes, although their development is governed by somewhat differ- 
ent conditions and there may be, and usually are, a number of broods during a 
season. Here the determining factor is the flooding of the marsh, either by 
rains or by a high tide, the higher ground along the beach preventing the escape 
of the water. Here again the eggs lie buried in the mud or sod and hatch when 
submerged, and here, also, a part of the eggs lie over until another flooding of 
the marsh. On the Pacific coast, where no rains occur for many months, a crop 
of salt marsh mosquitoes appears every four weeks following the monthly high 
tides that overflow the upper reaches of the marshes where the eggs are. All 
these species in which a long unfavorable period is passed in the egg state are 
closely related and belong to the genera Aédes and Psorophora. The genus 
Psorophora is most adapted to the conditions in the semi-arid tropics. Simul- 
taneously appear, and developing with equal rapidity, the non-predaceous larve 
of the subgenus Janthinosoma and those of Psorophora proper which prey 
upon them. 
In marked contrast to the forms just discussed are those which breed con- 
tinuously, as long as breeding-places exist and temperature conditions are 
favorable. Such are the forms in which the eggs are deposited upon the water 
and which hatch soon after being deposited ; these are the species of Anopheles, 
Culex, Culiseta, Uranotenia and Lutzia. The growth of the larve depends upon 
food conditions and upon temperature, so with these forms there are no well- 
marked broods or generations; adults and larve in all stages may be found at 
all times until frost cuts the larve off. As it is the hibernating females that pre- 
serve the species until the following season, and many of these females die off 
in the course of the winter, these species first make their appearance in small 
numbers and gradually increase to the end of the season. Never, however, do 
they reach such enormous numbers as the periodic species. To the continuous 
breeders belong the house mosquitoes which breed in rain-water barrels or other 
artificial receptacles. Other species of Culex breed in natural pools of a more or 
less permanent character, in swamps, or along the margins of streams. Others 
breed in the water of various water-bearing plants, such as the bromeliads, Heli- 
conia and Calathea of the tropics. In these continuous breeders the eggs are 
laid upon the water and develop at once, hatching within a few days. Certain 
forms of Aédes take a position intermediate between the forms with well-marked 
broods and the continuous breeders. Such are the species of Aédes and Stego- 
conops which breed in the water in hollow trees and in similar situations. With 
these the eggs are laid above the water line and they hatch when the water 
rises to them. As the result of successive rises, due to rains or other causes, 
eggs hatch at brief intervals and larve of various sizes are always present. Thus 
mosquitoes of these species are continuously present while there is warm 
weather and occasional rain. 
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