256 TREUBIA VOL. Il, 2—4, 
fastened round a hoop of rattan, the space inside the hoop being closed 
by a circular piece of cotton. In the centre of this cotton top-piece there 
is at the outside a loop to which is fastened one extremity of a long 
elastic piece of split bamboo. The other end of this piece of split bamboo 
is fixed in the ground in such a manner that the bamboo, which is 
slightly bent and therefore resilient, keeps the mosquito-gauze stretched. 
These mosquito-nets present the advantage that they do not drift away, 
being kept in the exact spot where they are fixed, and yet are able to follow 
vertical movements of the water surface which may occur in connection 
with the admission or draining away of pond-water. There is also a 
second advantage. The bamboos forming the lower frame can be with- 
drawn one by one from the hem at the bottom of the gauze, after which 
the net can be closed and tied under water. When the loop at the top 
of the net is detached from the long piece of split bamboo, the mosquito- 
gauze kept open by the rattan hoop, with all the mosquitos caught, forms 
an exceedingly light burden. Fixing them by the top-loop to along stick 
or bamboo a coolie can then with the greatest ease carry ten or more 
of these nets with the mosquitos caught, from the spot where they are 
caught to the place, a long distance off in our case, where the captured 
mosquitos must be determined and counted. 
It was the practice to set several of these nets at the same time in 
the same breeding-place, for which the staff of the Public Health Service 
were employed. In this connection a breeding-place should be understood 
as meaning a fish-pond, or speaking more accurately, as will appear from 
what follows, that part of a fish-pond where the submerged vegetation 
described in Chapter IV and represented in our photos 2, 3, 4, 6, 8, 9, 
14 and 15 (Plates VII, VII, IX, XI, XIV, XV, XXII and XXIII), has devel- 
oped. As may be seen from the observation-table (Table IV), it was usual 
to set 7 to 10 or at least 5 nets together in one and the same breeding- 
place. Occasionally we had to be content with fewer than 5 nets per 
breeding-place; this however occurred only in January and February 1919. 
The nets were set in the afternoon and taken in the next morning. The 
corresponding samples of water and submerged vegetation were gathered 
in the morning when the nets were taken in. The number of times a set 
of nets was put out in the Batavia marine fish-ponds was 399. 
Besides this Anopheline larvae and pupae were collected from the 
Batavia empangs 247 times by coolies under the direction of the staff of 
the Public Health Service, mostly from the same breeding-places in which 
a set of mosquito-nets had also been placed. I have already related above 
that it was then only possible to determine and count the imagines (22) 
that developed from the larvae and pupae collected. 
In SCHÜFFNER and SWELLENGREBEL’s Guide for the epidemiological 
malaria-research (Handleiding voor het epidemiologisch malaria-onderzoek) ($'), 
it is rightly remarked on page 53 that when studying an Anopheline 
