214 MOSQUITO LARViE AND THEIR NATURAL ENEMIES. 



'^ This is well illustrated by two examples : 



(a.) I have not found any larva? in the swamps at Vieux-Fort nor 

 in any pools of water that are in any way connected with the 

 main swamp. I'his is because all the pools are reached by the 

 ' Millions ' fish, which will be described later. 



(h.) I have not found larvas in a lagoon at Anse-la-R;iye ; but I 

 have found them repeatedly in pools around the lagoon, and 

 which are connected with the main sheet of water. The reason 

 is that th^ lagoon contains numerous dragon-fly larvae and 

 Grustacea,Which apparently do not invade the small connected 

 pools in the same way as the ' Millions^ fish. 



(7.) After rains, fresh pools are formed in the valle3's, along the edges of 

 the sugar-cane fields, along the sides of roads, and along the irregular 

 beds of the rivers, and these are not connected with the rivers, lagoons, 

 or any main sheet of peruianent water, in the neighbourhood. These 

 are the situations in which the Anopheline larvae are usually found. 



(8.) Cellia argi/rotarsls is found chiefly from the end of August to 

 November, and usually in situations as described in (7), especially when 

 there is protection afforded by matted decaying vegetation and the 

 finer grasses ; they occasionally occur, however, in pools on the 

 surface of' which are funoi and aloae, and where there is little or no 

 decaying matter or sedges. These pools occur in the sandy beds of 

 rivers and are protected from the sun, wind and rain by the over- 

 hanging giant vegetation. 



Cellia alhipes is found chiefly after November, and in shallow water 

 on marsh-lands, and is usually seen feeding on and protected by a 

 certain alga, which grows in a network above and below the surface ; 

 this network affords the larva protection from its natural enemies, 

 except the ' Millions ' fish which quickly penetrates it. 



" I am performing laboratory experiments with the mosquito larva? (Ano- 

 pheline), and find that they will not develop if there is an entire absence 

 of surface food. A deep beaker was filled with marsh water and allowed to 

 stand several days until all matter had sunk to the bottom ; larvae were then 

 placed in it ; they started to die after six days, and the last died on the 

 fourteenth day. In other experiments they have lived longer but have 

 not developed. Control experiments were of course always made and 

 the larvae {Cellia alhipes) hatched out. Another experiment was made 

 allowing sprayed water (imitation rain) to fall for twenty-four hours on the 

 surface of water that contained larvae. The larvae were destroyed. I have 

 also experiuiented with their food supplj^ : sedges and weeds are sterilised 

 and placed in sterilised distilled water, and the larva? having been passed 



