226 



J. W. SCOTT MACFIE. 



Table II. 



The Salinity of Thirty Samples of Water in which the Larvae of Stegomyia fasciata 



were found breeding. 



Chlorine in parts per 

 100,000. 



Under 



2 



2-2-9. 



3-3-9. 



4-4-9. 



5-5-9. 



Over 

 5 9. 



Number of samples examined 

 which belonged to each 

 group 



1 



15 



3 



6 



2 

 6-6 



3 



Percentage 



3-3 



50-0 



10-0 



20-0 



10-0 



The highest proportion of chlorine (20 5 parts) found in water in which S. fasciata 

 larvae were breeding was equal to only 032 per cent. NaCl. These observations 

 suggest that t^:. fasciata selects water containing but a trifling proportion of salt for 

 breeding purposes. 



An attempt was made to determine by experiment whether or not S. fasciata 

 did actually select her breeding place in this way. Cigarette tins were placed in pairs 

 in various parts of the laboratory where it was thought mosquitos might be lurking, 

 and in one of the tins 2 per cent, salt solution was placed, and in the other tap 

 water. The result of the experiment was not conclusive, as larvae developed in 

 only one of six tins set out. The one tin in which larvae did develop was, however, 

 a tin containing tap water. The experiment was repeated with 2 per cent, salt 

 solution and tap water to which a little broth had been added to make the media 

 more nutritious ; but the result was exactly the same, namely, larvae of S. fasciata 

 developed in only one tin, a tin containing tap water. 



In another experiment nine S. fasciata mosquitos (eight females and one male) 

 that had already fed were introduced into a large glass jar at the bottom of which 

 there was a layer of 2 per cent, salt solution in which a small beaker containing 

 tap water was immersed. The mosquitos had therefore the choice of a large surface 

 of saline solution, or a small surface of tap water, on w^hich to lay their eggs. 

 Two days later over a hundred eggs were found to have been laid on the tap water^ 

 but on the saline solution there were only four eggs, and these must have been killed 

 almost as soon as they were deposited, for they had not hardened, but were still 

 quite soft and white. In this single experiment the mosquitos certainly showed a 

 preference for the tap water, and a corresponding reluctance to lay their eggs on 

 the saline solution. 



On several occasions larvae of S. fasciata were transferred from the water in which 

 they were found breeding to another medium containing a high proportion of 

 chlorine in which larvae of C. decens or 0. irritans were flourishing. The Stegomyia 

 larvae were always killed by the change, and the results were identical with those 

 obtained in the experiments carried out at Lagos referred to in my former paper. 

 In a medium containing 2,000 parts of chlorine (328 per cent. NaCI) in which 



