306 The Two-winged Flies 
of yellow fever and filariasis, and to Anopheles belong the malaria breeding 
and distributing mosquitoes. 
All the mosquitoes agree in having strictly aquatic immature stages. The 
eggs are laid on the surface of standing or slowly moving water, usually 
fresh, although several species breed abundantly and probably exclusively 
in brackish water. These eggs are in small one-layered packets or rafts (usual 
in Culex) (Fig. 413) or are scattered singly (in Stegomyia and Anopheles) (Fig. 
414) and hatch in from one to four days, varying with the species, and in 
the same species with the temperature and light 
conditions. The water oviposited on may be, for 
Culex, that of a pond, a pool, or any temporary 
puddle, or even that in an exposed trough, barrel, 
pail, or can. With Anopheles only natural, usually 
permanent, pools are selected. I have found the 
eggs of Culex incidens on the surface of a bubbling 
soda-spring in California, and of Stegomyia in water 
held in slight depressions in a number of ship’s metal parts in Samoa. 
The brackish-water species of Culex usually lay their eggs on the small 
clear pools scattered through the marshes. A few entomologists have 
recorded their belief, based on various indirect observations, that the eggs 
of Anopheles at least may be deposited on the soil, but no direct proof of 
this is yet on record. 
The larvae (Figs. 413 and 415) of mosquitoes are the familiar wrigglers of 
ponds and ditches. The long, slender, squirming body, with its forked posterior 
extremity and thick head end, is thoroughly characteristic. The head is 
provided with a pair of vibratile tufts or brushes of fine hairs which are 
kefft, most of the time, in rapid motion, creating currents of water setting 
toward the mouth, and thus bringing to it a constant supply of food, which 
consists of organic particles and microscopic animals. Breathing is accom¬ 
plished by the wrigglers coming to the surface and hanging head downward 
from it with the open tip of the respiratory tube, one of the prongs of the 
posterior forking of the body, projecting just through the surface film. If a 
mosquito wriggler is prevented from coming to the surface, or if, once there, it 
finds some impediment which restrains it from getting its respiratory tube 
into connection with the free air above the surface, it will drown. And 
this fact partly explains the fatal effectiveness of a film of kerosene spread 
over the surface of a pool in which mosquitoes are breeding. The larval 
stage lasts from one to four weeks, varying in different species and also 
varying in the case of each species at different seasons and under different 
conditions of food-supply, temperature, and light. Larvae of Culex have 
lived in breeding-jars in my laboratory for three months. The larvae moult 
twice, and on the third casting of the skin appear as active, non-feeding 
Fig. 414. —The eggs of 
Anopheles sp. (After 
Giles; much enlarged.) 
