BREEDING OF AEDES CALOPUS 445 



laid from four to seven days after a blood meal. The nearest 

 allies of this species are tree-hole breeders, but the yellow fever 

 mosquito has become domesticated to such an extent as to much 

 prefer a rain barrel or water-filled tin can in a garbage heap, or, 

 even better, a water-pitcher or flower- vase indoors. Churches 

 in Central America are usually well supplied with yellow fever 

 mosquitoes which breed in the holy-water fonts. 



FIG. 203. A yellow fever center in Panama in the pre- American days. (Drawn 

 from photo from Thompson.) 



The eggs (Fig. 193C), up to 150 in number, are laid in several lots 

 at intervals of a few days, either on the surface of the water, or, as 

 is more common, on the edges of the container, or on a partially 

 submerged object, wherever a moist surface is presented and where 

 a slight elevation of the water will submerge them. The female 

 mosquitoes die a short time after the last batch of eggs is laid. 

 According to Bacot's experiments the promptness of hatching 

 depends 011 temperature and on whether the eggs have been kept 

 under moist or dry conditions. The eggs of this species retain 

 their vitality for several months when kept absolutely dry, but 

 they hatch more readily and with less mortality if kept moist. 

 When the eggs are laid directly on the surface of water they ma- 

 ture less rapidly than when laid above the surface, probably on 

 account of the cooling effect of the water. Eggs laid on the 

 surface hatch in a minimum of two days, while those above it, 

 if later submerged, may hatch in less than 12 hours. According 

 to recent work by Atkin and Bacot, eggs will not hatch in sterile 

 water, but will hatch within a few hours after the introduction of 

 living bacteria. The larvae (Fig. 204) thrive in either clean or foul 



