N. H. SWELLENGREBEL AND J. M. H. SWELLENGREBEL-DE GrAAF 1 91 
% 
to be the only Anophelines infected, all others, including M . aconita and 
N. maculatus, failing to show malaria parasites. In this case we must admit 
one or both of these species to be a possible vector, although the indirect 
index pointed to N. maculatus as being the principal vector. 
6. M. umbrosus. This species was found infected but once. Experimental 
infection succeeded with tertian only, at a rate much below that of M . sinensis. 
Therefore M. umbrosus cannot be admitted as the cause of a severe epidemic, 
moreover, the indirect index never pointed to its being a dangerous species; 
still we mention it separately, because Watson (1911) considers it to be the 
chief vector in the plains of the Malay Peninsula, and Barber (1918) succeeded 
m infecting specimens from some localities and not from others. We presume 
therefore that its infectivity is variable, and it should, at least, be suspected. 
Nevertheless, M. umbrosus has not the importance which attaches to M. aconita , 
N. maculatus and M. ludlowi. 
7. In this section we shall consider certain species with a relatively low 
N. I. (under 1 per cent.), although in epidemic regions the N. I. may rise to 
3 per cent. (M. rossii). The species in question are M. rossii, M. barbirostris , 
N. punctulata (tesselata ), and M. indefimta. These species are not confined to 
malarious regions. We are inclined to include C. kochii in this category although 
Schiiffner (1918 b) once found it to be more highly infected than the presumed 
local vector (M. aconita ). 
All of these species have been infected experimentally, but it would appear 
as if natural infection of the vectors is small in regions of low endemicity owing 
to the paucity of gamete-carriers. Of the species enumerated, M. indefinita is 
the least important. 
8. S. aitkenii (with its larval varieties insulae florum and papuae). 
Further information regarding this species is required. It was found ex- 
clusively in highly malarious regions associated either with M. aconita, 
, N. maculatus, or N. annulipes var. moluccensis. The last species is the most 
common Anopheline in the eastern part of the Malay Archipelago; regarding 
its infectivity we can say nothing for the present. Furthermore we have failed 
to find natural infection in M. ftava, M. albotaeniatus, M. maurilianus, M.gigas, 
N. schuffnerii, N. jamesii, and N. kawarii. 
Arranging the above species with regard to their epidemiological signifi- 
cance, we obtain the following sequence: 
(1) Myzomyia ludlowi ; (2 ) Myzomyia aconita ,, Nyssorhynchus maculatus , 
(perhaps also Stegomyia aitkenii ); (3) Neomyzomyia leucosphyra, Myzorhynchus 
umbrosus ; (4) Nyssorhynchus fuliginosus, Myzorhynchus sinensis (? = No. 6): 
I * \ 1 m /I / / /a m 7. ^ 7. . ' . / O \ 1 ^ v . _ 
(5) Cellia kochii ; (6) Myzomyia rossii, Myzorhynchus barbirostris , Neomyzomyia 
punctulata (tesselata)', (7) Myzomyia indefinita. 
Parasitology xn 
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