116 PROCEEDINGS ENTOMOLOGICAL SOCIETY 



once evident a difference in the time of appearance of the disease 

 after the men were encamped in the forest. In the second case the 

 disease would appear much later than in the third. But the first 

 alternative might show either a long or short period, according to 

 what the actual mode of infection was, whether by the infection of 

 local overlooked Anopheles from latent cases among the men them- 

 selves or by infection of the men individually outside of camp by 

 already infected mosquitoes. 



But whatever explanation be the true one, the burden of proof 

 rests upon the investigator, in this case Dr. Lutz, and we have the 

 right to expect that proof should be complete or to reject the 

 explanation offered." 



Continuing the discussion Mr. A. H. Jennings said: "In 1909, a 

 survey of the basin of the Chagres River in Panama was made by 

 the engineers of the Isthmian Canal Commission. The parties 

 engaged on this work suffered from malaria and in March of that 

 year I was instructed to make a general investigation of the mos- 

 quito fauna of the region with special reference to the sources of 

 malarial infection. The Chagres, Boqueron and Pequini rivers 

 were ascended, the latter to within a few miles of its headwaters, 

 and a careful study was made of mosquito conditions along all of 

 the streams traversed. 



Except along their lower courses, the country through which 

 these rivers flow is uninhabited and seldom penetrated by the na- 

 tives, who venture into the interior during the height of the dry 

 season only. The dry season is so only in name in the country 

 surrounding the sources of the rivers comprising the Chagres sys- 

 tem; heavy rains and sudden floods occur even during this season 

 and few days pass without more or less rain. 



I found Anopheles albimanus Wied., the principal malaria carrier 

 of the Panama region, to be entirely absent from the uninhabited 

 country and this was not from the lack of suitable breeding places, 

 as many such were found. The only species of Anopheles present 

 along the upper reaches of the rivers were eiseni and neivai. The 

 former I found breeding with some freedom in pools at the rocky 

 edges of the rapid streams and also in tree-holes, both situations 

 being characteristic of the species. Anopheles neivai was found in 

 the leaf axils of bromeliads and was not found in any abundance. 



