﻿392 The Philippine Journal of Science i9u 



the borders of the lake the land is low and is for the most part 

 devoted to the cultivation of rice with abundant irrigation from 

 the numerous streams flowing through it. At a distance of 

 several kilometers from the lake, the land rises to an extensive 

 undulating plain elevated from one hundred to several hundred 

 meters. This region is a part of the old Friar lands, devoted to 

 the cultivation of sugar for many years during the Spanish rule. 

 During the insurrection, in the latter years of the Spanish domi- 

 nation, much of it was laid waste and grew up to cogon grass or 

 jungle. Since the American occupation it is rapidly being re- 

 claimed and devoted to sugar cultivation again, both by the Fili- 

 pinos in a small way and by several American and European 

 companies on an extensive scale. The soil is fertile and un- 

 usually well watered. The region is crossed by numerous small 

 rivers and brooks, many of which are fed by springs and flow 

 throughout the dry season. These streams are peculiar in that 

 they have in most cases cut deeply into the soil, forming deep 

 ravines, and often into the underlying soft volcanic rock, form- 

 ing caiions. The banks of the streams are for the most part 

 densely covered with jungle vegetation. The lake, the extensive 

 irrigated rice fields, and the innumerable rivers and brooks in 

 this country aff'ord abundant and varied breeding places for 

 mosquitoes and furnish unlimited collecting grounds for the 

 species of anophelines that occur in this region. 



All of the mosquitoes used in our experiments have been col- 

 lected and bred from larvse. The species considered in this 

 paper were all collected in Laguna Province on the Calamba 

 Sugar Estate and adjacent country, with the exception of the 

 strain of Anopheles rossii that breeds in brackish or salt water, 

 the larvae of which were collected in esteros on the borders 

 of Manila Bay, about 50 kilometers distant, and brought to 

 Canlubang. 



COLLECTING LARV^ OF MOSQUITOES 



In collecting larvse in the brooks and rivers, it has been found 

 advantageous to wade the stream, preferably against the current. 

 In this way the breeding places are more accessible, and it is 

 often the only way to penetrate the jungle or to gain an entrance 

 into the caiions peculiar to the region. 



A variety of methods were tried in collecting larvse. At first, 

 white porcelain evaporating dishes, about 14 centimeters in 

 diameter, were used. By dipping these dishes into every sus- 

 picious-looking pool, the larvse, if present, were readily seen 

 against the white background. When larvae were found, the 



