DISPERSAL OF ANOPHELES 261 



at least two and a half miles from the nearest breeding place, and 

 Christophers has noted an instance in which male anophelines have flown 

 at least four hundred yards. 



In addition to the direct method of dispersal, anophelines may become 

 distributed over an area indirectly. All the newly hatched imagines of 

 any brood do not necessarily arrive at the same feeding ground as that 

 from which the parent came, nor do mature females necessarily return to 

 the same breeding place on each occasion to deposit their eggs, or return 

 after oviposition to the same house. Starting from any given centre, 

 therefore, breeding places may become established along any radius, 

 provided that suitable collections of water and food supply are available ; 

 each of these secondary breeding places may in turn become a centre for 

 dispersal, until eventually the species may be found breeding at a very 

 considerable distance from the place at which it originally occurred. At 

 Mian Mir, for instance, James found that culicifacies was able to spread 

 from the surrounding villages into the lines occupied by the British 

 troops by means of isolated houses and breeding grounds between the 

 two. Such breeding places as are of a permanent nature will serve as 

 sources from which surrounding temporary pools may be stocked at the 

 proper season. 



In a few cases anophelines are distributed along the ordinary lines 

 of transport, in carts, railway carriages, river boats, and from port to 

 port in ships. Should the conditions at the place at which they arrive 

 be favourable they may become permanently established there. 



Larvae of Anopheles may be carried long distances down irrigation 

 channels, in which the flow is intermittent, and those which survive may 

 set up new foci. During the anti-malarial operations at Mian Mir the 

 larvae of culicifacies were found to be transported in this way into areas 

 from which the imagines were absent. 



It has already been stated that we are without any reliable cri- 

 terion by which the age of a captured anopheline can be judged, or 



by which the number of batches of eggs which it 



, " , , , , , ,. , j c , ... i , Age Composition 



has laid can be established. Such a criterion would of Anophe i es 



be of great assistance in solving many problems Communities 

 connected with the bionomics of mosquitoes, and 

 in the study of the epidemiology of malaria. The question has been 

 attacked recently by Christophers, and although his preliminary work 

 has not led to any definite conclusions, the subject is of so much 

 importance that an account of it is necessary. 



Christophers, after first describing the development of the ova 



