256 MEDICAL ENTOMOLOGY 



The subject is a difficult one, for a large number of observations must be 

 allowed to accumulate before reliable conclusions can be drawn, and 

 workers in this field are severely handicapped by the difficulty which 

 exists in imitating natural conditions sufficiently closely to enable one to 

 carry out prolonged and exact experiments w r ith mosquitoes in captivity ; 

 the lack of any reliable criterion by which the age of any given specimen 

 can be judged has also proved a serious obstacle. Although a good deal 

 has been ascertained with regard to the breeding habits of the more 

 important species, their seasonal prevalence, their mode of spread from 

 one locality to another, and the manner in which they tide over the cold 

 weather or an unfavourable season, there are many subjects of almost 

 equal importance on which our knowledge is very scant}". Among 

 these might be mentioned the relations of the sexes with reference to 

 copulation and feeding, the length of life and the conditions which 

 determine it, the number of batches of eggs and the time at which each 

 is laid, and the choice of host in the different species. Almost all the 

 observations recorded have been made on female anophelines, and very 

 little is known about the male. 



As the larvae and pupae of the Anophelina are aquatic and free- 

 swimming, the essential condition for their breeding is a collection of 



water which will last sufficiently" long to enable them 

 Breeding Habits 



to complete their early stages, and which is either 



stagnant or flows just slowly enough not to wash them away ; food 

 material will usually be abundant wherever there is organic matter. 

 Such a condition is to be found almost anywhere, but in addition there 

 are some subsidiary requirements, more or less peculiar to the species, 

 which have to be fulfilled, each species exhibiting a predilection for some 

 particular environment, so that out of the half dozen or so Anopheles which 

 may be prevalent in any locality, only two or three will be found in the 

 same breeding place. The choice is more restricted in some species 

 than in others. 



A large number of the Anophelina breed in running water, and the 

 larvae of many of the species may be collected from the edges of rivers 

 and streams, where they obtain shelter among dead leaves, sticks and 

 other debris which collects in such places. In small streams which run 

 along dry river beds, and where fresh water collects in pools, larvae can 

 usually be found. Many other species breed in rain water puddles, in 

 rice fields, in irrigation channels, and in wells and tanks. Several 

 species, for instance, Anopheles ludlowi, and Anopheles Stephens!, habit- 

 ually breed in brackish water, and the latter even in sea water along the 



