414 JOURNAL, BOMBAY NATURAL HISTORY SOCIETY, Vol. XX. 



contain a mixture of fresh and sea water. Very many of these 

 contain larvee of N. stephensi during the monsoon when there is an 

 extra amount of fresh water there. 



Fresh water is not absolutely essential to mosquitoes, and it is 

 probably the motion of the waves rather than the salt water which 

 keeps many parts of the sea coast free of mosquito larvte. Mosqui- 

 toes do not hesitate to lay their eggs upon sea water; and the 

 larvas will hatch out and live in it ; but larvse, which have 

 hatched out in fresh water, usually die when placed in a mixture 

 containing 66 or 75 per cent, of sea water. Not long since 

 I received from Colaba a sample of living mosquito' larvas taken 

 from a shore pool. I estimated the amount of salt present in the 

 water and found it 25 per cent, more than in ordinary sea water. 



You will see from what I have been telling you that the distri- 

 bution of 2V". stephensi is very wide, but is not by any means uni- 

 form, as may be shown by the fact that, over three hundred breeding 

 places of this mosquito have been found in the North Fort Section 

 and only two in Khara Talao. The existence of suitable breeding 

 places has a great deal to do with this variation, but- does not 

 entirely determine it. It has been noticed that where favourable 

 breeding places occur in close proximity to one another a larger 

 proportion is infected than is the case where potential breeding 

 places are more widely separated. 



Originally, JSf. stephensi must have been largely restricted to 

 breeding in wells, tanks and fountains, but the introduction of a 

 pipe-water supply, on the intermittent system, and the adoption of 

 the water-carriage system of sewage disposal, has led to the erection 

 in every part of the city of large numbers of cisterns many of which 

 serve as breeding places of mosquitoes: The negligence which has 

 allowed the use of open and improperly closed cisterns is largely 

 responsible for the wider distribution of dangerous anopheles. 



Certain factors also appear to influence the distribution of 

 ISfyssorhynchus stephensi, tending on the one hand to favour its 

 spread, and on the other to restrict it, and limit its numbers. 



Among influences which tend to widen the distribution of this 

 and other species of mosquitoes, vehicles appear to play a consider- 

 able part. During the monsoon a hundred vehicles, including 



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