50 The Control of Mosquitoes 



subject to some variation. It would seem that the 

 white-footed group is undergoing some variation with 

 regard to the size and location of these hairs, and 

 apparently they are becoming rudimentary on the 

 thorax and first abdominal segment. 



The larvae are easily frightened and remain 

 hidden under water during long intervals, and for 

 that reason are sometimes difficult to detect. 

 Experiments were made by immersing larvae in 

 cages in the body of water from which they were 

 taken, and it was found that some of them re- 

 mained alive under water for a period of two hours, 

 even though the surface of the water was covered 

 with oil after the cage was immersed. It is not 

 widely known that Anopheles rest and remain upon 

 dark clothing for relatively long periods although 

 the wearer may be walking rapidly. It has been 

 ascertained by observation that in this manner 

 people convey them into houses that have been 

 properly screened. Large numbers are carried 

 long distances by trains at night. One obser- 

 vation was made in a case where a mosquito 

 (genus unknown) resting on the shoulders of a 

 man wearing a dark blue serge coat was carried 

 from Colon to Porto Bello on board a steamer. 

 The time of the trip was nearly three hours, and 

 the distance about twenty miles. Observers were 



