_266 TREUBIA VOL II, 2—4. 
considerable measure by the large numbers of kepala timah which are 
nearly always present there. | have consequently arrived at very much the 
same conclusion as for instance WILSON (47) and SEYMOUR SEWELL and 
CHAUDHURI (°°), from both of which authors I have already quoted in 
Chapter VI a few passages bearing upon the problem under discussion. 
On the other hand we have already seen before that, even where large 
numbers of kepala timah are present, the mosquito production in the empangs 
containing floating algal masses or higher submerged plants reaching up to just 
beneath the surface of the water is by no means reduced to nil. All sorts of 
factors finally contribute to prevent the consumption of all the larvae and pupae 
present in the ponds by these little fish, however eager they may be in devouring 
larvae and pupae. Something similar will also be often the case in other 
breeding-places than the empangs. Hence it may be but very rarely expec- 
ted that the introduction of animals preying on mosquito larvae and pupae 
in a natural breeding place of mosquitos should prove an absolutely effective 
means of combating the mosquito-pest or the malaria-peril. 
I have gone into this question of the importance of Haplochilus panchax 
(HAM. BUCH.) as an eradicator of mosquito larvae and pupae in some 
detail, because SWELLENGREBEL (%) recently thought himself obliged, on 
the strength of some experiments and a few observations, to arrive at 
conclusions which do not agree with my views as stated here. 
In the article in question by SWELLENGREBEL (°) three little fish are 
discussed as destroyers of mosquito-larvae and pupae, viz. Haplochilus 
panchax (HAM. BUCH.), Ophiocephalus striatus BL., and Dangila cuvieri C.\V.. 
Concerning Haplothilus panchax (HAM. BUCH.) it resulted from a 
simple experiment, for the purpose of which once 3 and twice 2 individuals 
were kept in 10 L. glasses, that as SWELLENGREBEL (2) himself says “this 
small fish is extremely voracious”, and that “two specimens may eat 100 
larvae in half an hour’s time”. These experiments were taken with animals 
freshly caught, which had therefore not fasted for any length of time. 
Thus far the experiments. Besides these SWELLENGREBEL (°?) examined 
the intestinal tract of 26 Haplochilus panchax (HAM. BUCH.) captured in 
sea fish-ponds in which a great many larvae of Myzomyia rossii GILES 
occurred. In the alimentary canal of only 2 of these he found remains of 
Anopheline larvae; the intestinal tract of 15 individuals contained other 
animal food, whilst the alimentary canal of the remaining fish contained 
nothing but “vegetable matter”). Furthermore SWELLENGREBEL (°°) in a 
1) It is not clear to me me what SWELLENGREBEL (2) means here by “vegetable 
matter”. Haplochiius panchax (HAM. BUCH.) is a pure carnivore, feeding exclusively 
on live animals. After reading the article by SWELLENGREBEL (©) discussed here 
I examined the intestinal contents si 84 more kepala timah. Only in one instance did I 
find any vegetable matter, namely a few small fragments of Chaetomorpha-threads in 
the intestinal tract of a kepala Eman which had a.o. eaten Gammaridea, Now these 
Gammaridea build dwelling-tubes of all sorts of fine vegetable matter, among which 
also Chaetomorpha-threads, These fragments of Chaetomorpha-threads had therefore 
probably been consumed together with the Gammaridea. 
