The test-pool experiment. 



and Eurasian houses. It is probable that since the introduction of 

 a pipe water-supply into Madras city, the numbers of this species 

 have largely increased, for its larvae are only found in those wells 

 which, since the introduction of the pipe water-supply, have been 

 unused. 



A, maculatus. The larvae of this species may be found further 

 from houses than those of A. rossi, and whereas larvae of the latter 

 species are usually found in muddy water, the larvae of A. maculatus 

 prefer clear sandy or rocky pools. In the Duars its larvae were 

 found in clear pools on a rice-field. In Hong-Kong (China) its 

 larvae were found by one of us in the small marshy pools on the 

 granite soil of Kowloon. 



Sumc.ent observations have not been made with regard to the 

 remaining species of " anopheles " to enable their favourite breeding 

 places to be particularised, but details of the breeding places in which 

 their larvse have been found will be given in Part II. 



Under unfavourable conditions the selection of suitable breeding 

 places by the different species is not of course so apparent, and 

 many instances might be given tending to show that if all the suit- 

 able breeding places near a village are dried up, " anopheles " will lay 

 their eggs on any collection of water of any kind. The " test-pool " 

 experiment of Stephens and Christophers in Africa is sufficient to 

 prove this, and the same expedient for finding out whether adult 

 " anopheles " are really present in a place or not, when all the natural 

 breeding places have disappeared, has been frequently resorted to 

 by observers in India. 



Even without making artificial pools in a village many examples 

 of the fact that in the absence of more suitable breeding places, 

 " anopheles " will lay their eggs in almost any collection of water, may, 

 be found in nature. In one part of Calcutta (Hastings) in Junes 

 when no breeding place could be found anywhere near, and no adults 

 could be caught in the houses, larvae were found in the cisterns of 

 water on the roofs of the houses. During the hot weather in 

 Mian Mir (Punjab) also, when the irrigation canals had been 

 stopped for some time, and there were no natural breeding place 

 of any kind, " anopheles " larvae were found in very curious 

 situations, as for instance in the swimming bath, in the horse 

 troughs, in tins of water accidentally left about, in the small drains 



52] 



