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SEASONAL VARIATION IN THE BREEDING PLACES OF ANOPHELES.
Early in the year until the rains begin to fall in May or June, breed-
ing places are scanty and widely separated. All the smaller streams are
dry and many of the larger ones contain but little water. At this time
large areas are absolutely devoid of surface water of any kind. The
first showers of rain have no appreciable effect, sinking rapidly into
the dry and porous soil, and though several inches of rainfall may be
recorded, the streams do not run, nor are any permanent surface pools
formed. But as the rains continue the streams begin to flow in certain
parts of their course and eventually with every succeeding downpour
they become swollen torrent; and in the case of gardens situated on
low-lying ground more or less temporory pools and swamps are formed.
At the height of the rains many of the torrents show no anopheles
larvæ ; but these are to be found in small collections of water of a
temporary nature that occur in the grass and jungle, or even in little
streams and drains which run intermittently and for the briefest period.
After the cessation of the rains during the months of September,
throughout October, and to a less extent during November and Decem-
ber, the streams fed by springs and the general soakage from their beds
become throughout most of their course stocked with the larvæ of ano-
pheles. By the end of December and the beginning of January the small-
er streams are dry or show only occasional small pools here and there,
or perhaps a few trickling springs, the condition we have described re-
sults, and for considerable distances there are no anopheles larvæ to
be found anywhere.
SPECIES OF ANOPHELES.
The common species of anopheles are M. lisloni, N. theobaldi and
P. rossi. The last species is fairly abundant in some places where
suitable breeding places occur; but it is not nearly so conspicuous
in the Duars as in many parts of India. M. barbirost ris is
found in great abundance in a few places; but is not widespread,
or common in the district. N. fuliginosis and A. elegans also occur,
but not to any great extent. A. sinensis is exceedingly common at
Jalpaiguri town, but rare in the Duars. M. Culicfacies, the common