The question to which we have tried to find an answer is why malaria is almost absent in the southern region (II) within our field of observation, whereas it is endemic in the northern (I). We found Anopheles slightly less frequent in the former, but the difference is irrelevant, and the density of the Anopheline population in Region II is considerable, compared with almost all the European malarious countries we visited and where A. maculipennis is the local vector.
If this difference in the incidence of malaria is at all caused by a difference of the Anopheline faunas of the two regions (which need not be the case), then the biological distinctions are the only important ones. Morphological differences cannot interest us unless they are correlated with the former. Still we began by studying the latter, because they are easier to observe and to measure.