344 J. W. SCOTT MACFIB — ACTION OF SALT ON STEGOMYIA LARVAE. 



tank like that shown in PI. XXXII. fig. 2 were reproduced in the laboratory by 

 means of tins in the bottom of which small holes were pierced. The tins were half 

 lilled with soil and small stones, and an inch of water was added on the top. 

 The drainage was arranged so that the surface of the soil became exposed after 

 about one hour. The artificial pools thus formed were filled up every morning, 

 and allowed to drain away as described. Thus a free surface of water was 

 present for about one hour each day only. The soil, however, remained moist 

 throughout the day. 



Into such artificial pools pupae, mature larvae, and young larvae of Stegomyia 

 fasciata were introduced. In the case of pupae the majority always hatched in 

 the course of three or four days. In one experiment started with ten pupae, four 

 had hatched within the first 24 hours, three more during the next 24 hours, and 

 two more during the third day ; only one pupa perished. Mature larvae were 

 found to be much less resistant to desiccation. They not infrequently pupated, 

 but in our experiments none of the pupae hatched. Young larvae also survived 

 only a short time, and did not undergo their normal development. Some of them 

 however, remained alive until the sixth day ; and it is possible that had the pools 

 been renewed more often, or allowed to persist a little longer, as no doubt they 

 often do under natural conditions, the larvae might have matured, pupated and 

 even hatched out into mosquitos. 



The chief danger of such occasional pools therefore is that pupae, washed into 

 them from other pools or from the gutters of bungalows, may complete their 

 development in them. But as even immature larvae may also live for a number 

 of days in such situations, it would perhaps be a wise precaution to treat these 

 places with larvicides. 



