228 



J. W. SCOTT MACFIE. 



Experiment XIV. 



Day of the 

 experiment. 



2 % salt solution. 



Tap water. 



1 



20 pupae of S. fasciata intro- 

 duced. 



20 pupae of S. fasciata introduced. 



3 



All the pupae have hatched. 



Three pupae remain. 



4 





All the pupae have hatched. 



5 



8 a.m. The first mosquitos fed 



8 a.m. The first mosquitos fed on 





on blood. 



blood. 



9 



No eggs yet. 



The first batch of egg^ laid. 



15 



No eggs, no larvae. 



The first larvae hatched. 



17 



No eggs, no la.rvae. 



More eggs laid. 



19 



No eggs and no larvae yet. 

 Saline fluid poured oif, and 

 replaced by tap water. 



More eggs ; and many larvae. 



20 



Eggs laid on the surface of the 

 water. 





21 



More eggs laid. 



First pupae seen. 



23 





First adults emerged. 



24 



First larvae hatched. 





30 



First pupae seen. 





32 



First adults emerged. 





On the tap water the first batch of eggs "was laid on the ninth day, and further 

 batches of eggs were deposited in rapid succession. On the salt solution, on the 

 contrary, no eggs had been laid up to the nineteenth day, but on replacing the salt 

 solution by tap water, eggs w^ere deposited immediately w^hich hatched into larvae 

 in the usual time. 



As this experiment was conducted with a relatively small number of mosquitos, 

 a large number of pupae, namely a hundred, were placed in 2 per cent, salt solution 

 in a large glass jar. All the pupae had hatched out by 8 a.m. on the third day, and 

 on the fourth day the females began to feed on blood. Although the experiment 

 AVas carried on for twenty-three days, no larvae appeared in the jar ; but on the 

 eighth day some white bodies were seen on the surface of the medium which 

 resembled newly -laid eggs. These bodies did not turn black, but on microscopical 

 examination it was evident that they were really eggs. They were quite soft, so 

 that the pressure of a coverslip was sufficient to burst them. These eggs, as they 

 were laid, must have been affected by the saline medium so profoundly and so 

 rapidly that they neither hardened, nor turned black. Later, a very few black eggs 

 were seen. As they were in the middle of clumps of the white eggs, it is probable 

 that at first they may have been protected from contact with the saline fluid. 

 They did not, however, hatch into larvae, so that presumably they were killed by 

 it later. 



These experiments seem to prove that the female S. fasciata either will not lay her 

 eggs on 2 per cent, salt solution, even when no alternative breeding place is offered 

 to her, or if her natural instinct compels her to do so, the eggs thus laid are rapidly 

 killed by the solution, and no larv^ae result. Experiments have not yet been carried 

 out with solutions of salt of a lower concentration than 2 per cent., but as the results 

 with this percentage were so pronounced, it is not improbable that weaker solutions 

 would have some similar deterrent effect. 



