Classification into groups containing closely allied forms. 



tropics. By placing individuals with similar characteristics in 

 groups the difficulties of deciding whether two individuals really 

 belong to distinct species are, to a great extent, overcome ; for the 

 general appearance, habits, and above all the pathological signifi- 

 cance of the species of each group are the same, and for those who 

 are unable to undertake the minute examination necessary to 

 accurately determine the species, it is of some advantage to 

 determine the group to which any specimen belongs. If two 

 individuals such as listoni and funestus, for example, are alike 

 in their general characters, in their habits and breeding places, and 

 in their power of carrying malaria or other tropical disease, it is 

 really unnecessary, except from a purely entomological point of 

 view, to separate them as distinct species. The object of the worker 

 on tropical diseases is to separate into distinct genera and species 

 only those insects which, from some marked difference in habits, 

 or from any other reason, exert a different influence on any tropical 

 disease. If, for example, it were proved that all " anopheles" mos- 

 quitoes were alike in habits and in their power of carrying malaria, 

 the tropical worker would have little object in separating them 

 even into different species : it would be sufficient for him to study 

 " anopheles" mosquitoes as a whole. It is known, however, that the 

 habits of different species differ markedly, and, for this reason, their 

 influence on the spread of disease must be different. A species 

 which habitually lives and finds its food apart from man cannot 

 have the same influence on the prevalence of malaria as a species 

 which is always found near human dwellings. In any rational 

 classification of " anopheles," therefore, the question of habits in 

 nature is a very important one of more importance, we think, than 

 a slight, though constant, structural difference in any one stage 

 of the insect's life. 



We have accordingly divided the Indian " anopheles" into ten 

 groups. 



GROUP I. 



The "anopheles" of this group are, as a rule, large black mos- 

 quitoes with long spidery legs. The wings are marked with two 

 minute yellow or white spots on the costal border. Very many 

 varieties occur among the mosquitoes of this group, to which 

 many names have been given. We have described two types, 



