LIFE HISTORY AND SEASONAL PREVALENCE 133 



that freezing for a couple of days, killed all the larvae, while no 

 pupae survived more than twenty-four hours. Desiccation, 

 on the other hand, was better borne by the nymphs, which 

 in a few days, were transformed into very active Mosquitoes, 

 in spite of being placed in dry river sand, so that the drying 

 up of a pool does not stop the developinent of such insects 

 as have reached this stage, while the larvae were all dead 

 in two days if dried at 20° C, and both stages were killed 

 by two minutes' exposure to a temperature of 40°. Experi- 

 menting in India, I found that larvae were usually dead and 

 decomposed before the mud of the pool in which they had 

 lived had dried up by ordinary evaporation. Nearly all 

 species can live only in fresh water, but Bancroft found a 

 species, which has been named marinus, by Mr. Theobald, 

 living in sea water, and Ficalbi collected the larvae of G. 

 nemorosus {salinus) in a salt marsh. 



Celli found that Anopheles larvae died within thirteen 

 hours in sea water, and could not live in mixtures stronger 

 than two parts of fresh to one of sea water, which agrees 

 with the results of Ficalbi's recent observations on the salt 

 marshes of Cervia, where he found that though they 

 abounded in neighbouring sweet water pools, they were 

 never present in the actual salt pools, and were only excep- 

 tionally found in even slightly brackish water. Stephens 

 and Christophers found that mangrove swamps never con- 

 tained Anopheles larvae, so that the idea that these salt- 

 water shallows are a cause of malaria is erroneous, though 

 one can well understand that a saturated atmosphere, reek- 

 ing with the emanations of vegetable putrefraction, may be 

 extremely unhealthy for other reasons. Moreover, although 

 they speak of them as being found in fresh water marshes, 

 it is evident from what they write that, strictly speaking, 

 they are no more to be found in such situations in Africa 

 than they are in India, as they proceed to explain that they 

 found them, not in the main marsh, but in the pools around 

 it. In running water, unless the current be very slow, they 

 cannot exist, and hence they are never found in rivers, 

 except in extremely sluggish streams, such as the Cam, 

 where Theobald mentions having once found them. 



