The present paper supplements and extends previous studies on the epidemiology of malaria. Evidence is presented which establishes the relationship of the climate and the bionomics of the local anopheles to the prevalence and periodicity of epidemic. It is shown that the distribution of rainfall and the prevailing temperatures (indoor and marsh) by affecting the type and conditions of anopheles breeding modify the intensity and recurrence of epidemics. Attention is also called to the fact that the biology and habits of the anopheles, and particularly their range of flight and dispersion have an important relation to the epidemiology of disease and the occurrence of epidemics in unexpected places and at unusual seasons. In studying epidemics of malaria more attention should be given to the range of flight and dispersion of mosquitoes, particularly where the houses are not scattered but grouped in compact villages.