166 SOME MINUTE ANIMAL PARASITES 



small quantities of water in which to lay its eggs, 

 and seven batches of eggs are laid successively. It 

 moves practically noiselessly, and bites by day as 

 well as by night, but is more or less quiescent 

 between 9 a.m. and 3 p.m. When a mosquito has 

 bitten a yellow fever patient, the virus needs twelve 

 to thirteen days in order to mature in the body of 

 the insect and to acquire its full virulence, and, once 

 infected, there is no evidence that it does not remain 

 infective for life. Further, the mosquito must bite 

 the patient during the first three or four days of the 

 illness in order to become infective. 



The Stegomyia has been mentioned as frequenting 

 houses. It selects cool, quiet, dark spots for egg- 

 laying, and does not seem as a rule to fly long 

 distances. It seeks cover as soon as hatched, and 

 is able not only to enter houses, but to penetrate 

 ships lying at anchor in the river or off the town. 

 Thus it happens to be the most common mosquito 

 aboard ships, and can remain concealed for long 

 periods. Egg-laying is preceded as a rule by a meal 

 of blood, human for preference. In Nature this 

 invariably occurs, and though Stegomyia in captivity 

 have been trained to live on plant juices, their ovula- 

 tion was greatly delayed and unsuccessful. The ova 

 are very small, but rapidly develop into " wrigglers " 

 or " wiggle-waggles," and it is astonishing how little 

 water is needed for their vigorous development. 

 In tropical towns it is wonderful how many un- 

 suspected breeding-grounds for larvae exist. In 

 African fishing villages, or where canoes are numer- 

 ous, the rain-water that collects in the boats teems 



