PROPHYLAXIS IN YELLOW FEVER 255 



mouth-parts are simple, the clumps of hairs, the brushes 

 situated on each side of the mouth are short, stiff, and 

 not very abundant. The mandibles and maxillae are 

 powerful. These larvae feed at the bottoms or sides ot 

 the water in which they live, and mainly on lower forms 

 of animal and vegetable life. They require abundant 

 food and serve to keep down algae. They can remain 

 under water for a long time, and often escape notice in 

 that way. When breathing or resting they hang with 

 their heads down from the surface of the water, and in 

 butts and barrels are often numerous enough to blacken 

 the surface of the water. Any slight disturbance appears 

 to alarm them, as the whole lot will then immediately 

 dive to the bottom of the barrel, and may remain there 

 for some time, and the surface of the water be free from 

 larvae. The larvae are very hardy, active in their move- 

 ments, and less readily killed by desiccation than most 

 larvae. The larvae live well on board ship. They require 

 a fairly high temperature and are killed when frozen. 

 They do not occur outside tropical and sub-tropical 

 regions. 



The adults imagines are hardy mosquitoes, and most 

 species feed readily on man. Some jungle species bite 

 by day only, many feed both at night and by day, but 

 S. fasciata at first will feed by day or night, but after once 

 feeding continue to feed at night only. Many species are 

 jungle mosquitoes, but some of these, as S. scutellaris, 

 are much more numerous in settlements in the vicinity 

 of jungle, and readily become domesticated. S. fasciata 

 is far more abundant on the sea-coast, and in many 

 countries, such as the Guianas and the Malay Peninsula, 

 is rarely met with except in coast settlements and towns. 

 Though strong, active mosquitoes, they do not take 

 extensive flights, or go far from their breeding-places. 

 It follows that when these mosquitoes are numerous, 

 the breeding-places are close at hand. As a rule, the 

 breeding-places of the mosquitoes are in the immediate 

 surroundings of a house and destruction of these 



