182
WILLIAM MACNAE
can as an adult live in salinities up to 28%, and as a tadpole in salinities
up to 39%,. Over most of the area of distribution such salinities will
rarely be reached in any mangal, disturbed or undisturbed. But
towards the limits of its distribution R. cancrivora lives in areas with
very marked dry seasons, and here much of the mangal has been cleared
and salt production carried out on the higher levels of the intertidal
flats. This frog occurs both as an adult and as a tadpole in the vicinity
of these salt pans. The experimental animals which Gordon et al. used
came from the vicinity of Bangkok where in December-January high
salinities may be encountered.
Gordon and Tucker (1965) state that the tadpoles are good osmoregulators, using mechanisms similar to those employed by euryhaline
teleost fishes. They suggest that the tadpoles probably drink the
hyperosmotic medium and excrete the salts by some extrarenal pathway. Adults (Gordon et al., 1961) show a strong convergence to
elasmobranch fishes, retaining urea within the body fluids. The change
from one mechanism to the other has not been investigated. It must
take place a t metamorphosis. I n Malaya, I was told by Lord Medway
that metamorphosis is induced by a heavy dilution of the water in
which the tadpoles are living. The development of the tadpole can
apparently proceed in brackish water but is arrested just before
metamorphosis ; at this stage the tadpole enters a state analogous to
the insect diapause, waiting for the flood of fresh water which will give
it the stimulus and the medium of low salinity in which metamorphosis
can be achieved. I n the ever-wet of Malaya this may be at any season
but in regions with wet and dry seasons metamorphosis will follow the
first flood of the wet season.
B. Insects
The insects associated with the canopy appear to be typical
terrestrial insects.
The weaver ants or tailor ants Oecophylla deserve some attention
(Fig. 58). These ants all look much alike and although several species
have been described many authorities would recognize only one, Oe.
smaragdina Fabr. Vanderplank (1960) and Way (1954a,b) have studied
these ants in relation to crops which are grown close to the sea. They
have shown that ants have various sizes of workers, soldiers and several
queens associated with each colony. Each colony comprises several
nests and usually all the nests in one tree will belong to one colony.
Their food is derived from two sources: they lap up the honeydew
produced by the coccids on the trees they inhabit, and, in addition to
this source of fuel, they require protein which they obtain by preying
WILLIAM MACNAE
can as an adult live in salinities up to 28%, and as a tadpole in salinities
up to 39%,. Over most of the area of distribution such salinities will
rarely be reached in any mangal, disturbed or undisturbed. But
towards the limits of its distribution R. cancrivora lives in areas with
very marked dry seasons, and here much of the mangal has been cleared
and salt production carried out on the higher levels of the intertidal
flats. This frog occurs both as an adult and as a tadpole in the vicinity
of these salt pans. The experimental animals which Gordon et al. used
came from the vicinity of Bangkok where in December-January high
salinities may be encountered.
Gordon and Tucker (1965) state that the tadpoles are good osmoregulators, using mechanisms similar to those employed by euryhaline
teleost fishes. They suggest that the tadpoles probably drink the
hyperosmotic medium and excrete the salts by some extrarenal pathway. Adults (Gordon et al., 1961) show a strong convergence to
elasmobranch fishes, retaining urea within the body fluids. The change
from one mechanism to the other has not been investigated. It must
take place a t metamorphosis. I n Malaya, I was told by Lord Medway
that metamorphosis is induced by a heavy dilution of the water in
which the tadpoles are living. The development of the tadpole can
apparently proceed in brackish water but is arrested just before
metamorphosis ; at this stage the tadpole enters a state analogous to
the insect diapause, waiting for the flood of fresh water which will give
it the stimulus and the medium of low salinity in which metamorphosis
can be achieved. I n the ever-wet of Malaya this may be at any season
but in regions with wet and dry seasons metamorphosis will follow the
first flood of the wet season.
B. Insects
The insects associated with the canopy appear to be typical
terrestrial insects.
The weaver ants or tailor ants Oecophylla deserve some attention
(Fig. 58). These ants all look much alike and although several species
have been described many authorities would recognize only one, Oe.
smaragdina Fabr. Vanderplank (1960) and Way (1954a,b) have studied
these ants in relation to crops which are grown close to the sea. They
have shown that ants have various sizes of workers, soldiers and several
queens associated with each colony. Each colony comprises several
nests and usually all the nests in one tree will belong to one colony.
Their food is derived from two sources: they lap up the honeydew
produced by the coccids on the trees they inhabit, and, in addition to
this source of fuel, they require protein which they obtain by preying