THE NATURAL HISTORY OF BOMBAY MALARIA. 415 



victorias, shigrams and broughams, were examined, in different 

 stables in the city. In the course of this examination it was 

 found that mosquitoes were invariably present in these vehicles, 

 unless they had been recently disturbed. The greatest number of 

 mosquitoes counted in one vehicle was 25. The greatest number 

 of N. stephensi was 13. Watching the behaviour of mosquitoes 

 occupying a vehicle that was being taken out from the stable, it 

 was found that most of them remained clinging to the hood or 

 inside the carriage until it had gone some distance ; but gradually 

 they became disturbed by the movements of the vehicle, and one by 

 one escaped and flew away during the course of the drive. 



These observations show the part played by covered vehicles in 

 the diffusion of mosquitoes from one locality to another, and indi- 

 cate one method by which N. stephensi tends to invade fresh areas, 

 reaching by artificial means, places to which it would not ordinarily 

 be carried, either by the wind or its unaided powers of flight. 



Among factors which tend to limit the number and restrict the 

 distribution of N. stephensi in Bombay, one of the most interesting 

 and important is the existence of another mosquito belonging to 

 the Culicine group. This mosquito, Gulex concolor, appears to exert 

 a directly antagonistic influence upon other mosquitoes, anopheles 

 in particular, because its larvae are specially adapted for preying 

 upon those of other mosquitoes. It is frequently found breeding 

 in the collections of water haunted by N. stephensi and destroys 

 great numbers as the following observations show. 



Four large larvae of Gulex concolor were placed in a bowl contain- 

 ing a number of larvae of N. stephensi of different sizes. These they 

 immediately began to seize and devour and in the course of two 

 hours they had destroyed over 50. They will act in a similar man- 

 ner under natural conditions as is shown by the fact that, breeding 

 places which early in the season contained large numbers of larvae 

 of N. stephensi, later in the year contained larvae of Gulex conco- 

 lor also ; and subsequent examination has shown that Gulex 

 concolor alone remained. 



The larvae of Gulex concolor does not seek its prey, but waits 

 for its approach. It usually assumes an almost horizontal position 

 just below the surface of the water, admirably suited for attack 



