that Anopheles pools, and consequently malaria, are seldom 

 found on hilly ground, and that both abound on level soil 

 and in flat valleys between hills. 



At the same time it must be understood that these rules 

 are not without exceptions. Thus larvae may sometimes 

 be found amongst the reeds and partially submerged grass 

 at the margins of lakes and rivers ; or in the little quiet 

 bays and creeks of streams ; or in the small pools lying at 

 the edge of morasses ; or in ponds full of weeds, or in sub- 

 merged rice-fields, even if these contain a certain number 

 of fish. They may also occur in very small puddles during 

 constant rainfall ; and, lastly, may exist in very large 

 numbers in the hollows of rocks left full of water by drying 

 watercourses at the end of the rains. 



The natural situations in which Anopheles larvae occur 

 differ to some extent according to the local conditions of 

 drainage and rainfall, but seem everywhere to be deter- 

 mined by much the same general laws. 



The larvae are sometimes found in artificial collections 

 of water, such as disused wells, borrow-pits, cess-pits, 

 garden cisterns, drain-outfalls, and so on. They may even 

 occur in vessels of water, such as water-butts; and are 

 frequently found in the bilge-water of boats lying idle on 

 shore. 



Occasionally, especially in the presence of thick jungle, 

 undergrowth, or long grass, it is very difficult to find the 

 breeding places of Anopheles at all. Sometimes numbers 

 of the insects collect round houses or encampments in the 

 middle of the bush, evidently attracted by human beings, 

 though it is not possible to discover their larvae anywhere. 

 In such cases it is probable that the breeding pools have 

 been overlooked owing to the copious vegetation, or that 



