66
Characters of the larva.—The frontal hairs of the larvae found in Bombay
possess a few fine lateral branches similar to those seen on the larvæof N.
stephensi. Palmate hairs are present on the thorax as well as on. the abdominal
segments ; they are generally large and prominent ; the leaflets are provided
with a well marked shoulder which is usually serrated and pigmented at the
origin of the terminal filament. The terminal filament is short.
Ovum.—Upper surface very narrow ; floats do not touch margin of upper
surface ; lower surface not ornamented.
Myzomyia Culicifacies.
150. There is no necessity to enter into a detailed description of this
mosquito which resembles M. listoni very closely. The specimens met with in
Bombay have been usually slightly larger and rather paler in colour than
IL listoni and possess a marked culicine attitude when at rest.
Major S. P. James mentions as a characteristic distinction between this
mosquito and M. listoni, the fact that the 1st fork cell is less than 11/2
times the length of the 2nd fork cell, and the wing fringe has 2 white areas
instead of 5.
Larva and Ova.—The larvæ and ova are indistinguishable from those
of M. listoni.
Section 2.
151. INFECTION OF MOSQUITOES.—In discussing the mosquitoes
of Bombay in relation to the spread of malaria the vast bulk of the insects that
exist in the City may be at once passed over. Neither the ubiquitous Culex
fatigans nor the annoying Stegomyia are dangerous from the point of view of
malaria, and other mosquitoes which belong to the Culicine family are non-
carriers of the disease likewise.
152. Among mosquitoes of the Anopheline family (to which the carriers
of malaria alone belong) there are, as has already been pointed out, 7 species
present in Bombay. By far the most common species is Nysso-myzomyia rossi.
It abounds everywhere and is often to be found in extraordinary numbers ; and
it is a matter of some importance to learn whether or not it is concerned in the
transmission of malaria in Bombay.
153. A large amount of evidence has been collected from time to time
which appears to show that N. rossi is not concerned in the spread of
malaria in India. In 1901 Stephens and Christophers, the members of the Royal
Society's Commission on Malaria, examined very large numbers of N. rossi
caught in dwelling-houses in Calcutta, Mian Mir, Ennur and the Bengal Duars
without finding a single infected insect. They record the dissection of 1,189
specimens, 860 of which were caught at Mian Mir and Ennur, at the same time
and in the same places as smaller numbers of M. culicifacies. In both stations
malarial parasites were uniformly absent from rossi whereas in specimens of
M. culifacies, sporozoits of malaria were present to the extent of 4.6 per
154. But although these observations of Stephens and Christophers aro
almost conclusive, it was felt that it would be wise to make absolutely sure
that rossi did not behave in a different manner under conditions present
in Bombay, and this point was investigated early in the course of the
enquiry. In 1908 Major W. Glen Liston, I. M. S., caught a number of adult
mosquitoes in dwelling-houses while investigating malaria near the New Docks
in the Frere Road. Among those mosquitoes two species of anopheles were
present, Nysso-myzomyia rossi and N. stephensi ; and examination of a number
of the latter resulted in the important discovery that they were infected
with malarial parasites in as high a proportion as 25 per cent. In view of this
fact the same locality was chosen as a suitable place from which to obtain
mosquitoes for systematic examination, and during the investigation adult
mosquitoes were caught there at frequent intervals, With few exceptions these
mosquitoes when caught were found to be full of blood, presumably derived from
the inmates of the houses in which they were found. Among these inmates were
many children who showed a spleen index of 70 to 80 per cent. and a parasite