27

PART II.

I.—OBSERVATIONS ON THE CHARACTERS AND HABITS OF ANOPHELES
MOSQUITOES AND THEIR LARVÆ.

       AT an early stage in our investigations it became evident that the number of
species of anopheles mosquitoes that exist in India was much larger than
had been anticipated, and that the descriptions of the anopheles which had been
recorded, both from India and from other countries, were so inadequate as to
render their identification difficult, if not, in many cases, impossible.

       Until recently, however, this was a matter of small importance from a
medical point of view, because the fact that some species of anopheles might
be more important than others in connection with the transmission of malaria
had not been generally recognised by observers, the majority of whom had
therefore been content with a study of the anopheles genus as a whole, without
recognising the importance of a study of each species separately.

       Our observations, however, have shown that the different species of ano-
pheles differ very markedly not only in their habits and breeding places, but
also in their relation to the prevalence of malaria in different places, so much
so, indeed, that whereas the presence of one species appears to be almost
always associated with a considerable amount of malaria, the presence of another
species appears to exert no influence whatever on the prevalence of the disease.

       For these reasons, if for no other, it is certainly of the greatest practical
importance to be able to identify the different species of anopheles correctly,
and to study the habits, life history, and pathological significance of each
species separately.

       Unfortunately, however, the classification of anopheles is at present in an
early stage, and the difficulties of identification of any particular species are
enhanced by the fact that a considerable number of anopheles mosquitoes have
been lately described as new species, which differ in only very minute respects
from existing species.

       It is doubtful whether all these so called new species are really distinct,
and it becomes necessary to enquire whether the characters by which entomol-
ogists separate closely allied species are sufficiently constant to be relied upon,
or whether the large number of species which differ but slightly from each
other are in reality only variations of one or two existing species.

       A. Culicifacies (Giles), for example, may be taken as a type of the group
which I have called the group of "small brown anopheles with unbanded legs."
The five following mosquitoes in India which resemble A. Culicifacies closely
have been described as new and distinct species :—A. Fluviatilis (re-named
A. Christophersi by Mr. Theobold), A. Listonii (Giles), A. Listoni (Liston),
A. Indica (Theobald), and A. Jeyporiensis, as well as the African species

E 2