140 



MOSQUITOES AND MALARIA 



[OH. 



on cloudy moist days, and others again may have actively diurnal 

 habits and feed by day like Stegomyia. An example of the 

 latter habit is seen in the species A . (Myzorhynchus) barbirostris, 

 which swarms in the forests of Malay and is most bloodthirsty 

 throughout the daytime. Another diurnal species is Anopheles 

 aitkeni. Even the boldness and persistence, or even the small 

 size of particular species, may add greatly to their effect in 

 transmitting malaria under particular circumstances. 



But in addition to these differences in habits which indirectly 

 affect the transmission of malaria, there is the very important 

 question of the relative suitability of different species of Ano- 

 pheles for the development of the parasite. When it was shewn 

 that certain species of Anopheles carried malaria and that 

 Culex and other biting insects did not, it was assumed that 

 the power to act as a suitable host to the malaria parasite was 

 common to all Anophelines. The first instance of an Anopheles 

 being shewn not to transmit malaria was in the case of the 

 common Indian species A. (Myzomyia} rossii. This species is 

 found quite commonly in very large numbers associated with 

 every degree of prevalence of malaria, but it has not yet 

 been shewn to act as a transmitting agent under natural 

 conditions, though it can be infected experimentally. Not 

 infrequently this species occurs along with others which are 

 actively concerned in the spread of malaria, but though under 

 these circumstances a considerable percentage of both A . (Myzo- 

 myia) culicifacies and A. (Nyssorhynchus) stephensi have been 

 found with sporozoites in the salivary glands, A. (Myzomyia) 

 rossii has never been found infected. This peculiar fact, re- 

 garding which the following independent figures have been 

 given, is not easy to explain, but there seems little doubt that 



