FAUNA AND FLORA O F MANGROVE SWAMPS
213
crab. His description was repeated by several authors, Ortmann (1901),
Bab&k (1921), Stebbing (1893) and by the compilers of the Cambridge
Natural History. Verwey (1930) elaborated the account having studied
S. mederi (= S. taeniolata), S. meinerti, S. bataviana and the freshwater
S. nodul-fera. The following account is from Verwey and has been
confirmed by undergraduate students working at Inhaca on S. meinerti.
When these species of Sesarma are immersed in water, it can be
demonstrated by the addition of carmine that water is taken in by way
of openings a t the base of the third maxillipeds (the so-called MilneEdwards opening), and also above the fourth and fifth walking legs,
and exhaled at the upper edge of the buccal cavity, When crabs
are in very shallow water the carapace may be raised to show above
the edge of the abdomen, a slit used for the uptake of a bubble of air
into the gill chamber. This process is usually rather one-sided, either
the right or the left side is raised. The musculature effecting this
movement has not been traced. Water is taken up from shallow
puddles by a different technique. The crab squats down so that the
Milne-Edwards opening is under water and Verwey has shown that
water is taken up during this period of squatting.
When the crabs are in shallow water or exposed to air, water is seen
to emerge from the exhalant opening and then to flow along three
grooves. Two of these lead directly to reticulated areas on the outer
surface of the branchiostegite, the other leads to the orbit and thence
by way of a narrow groove under the lateral margin of the back. These
streams of water flow over two apparently reticulated areas-that
flowing over a fronto-lateral area passes directly to the Milne-Edwards
opening ; that flowing over a lateral area passes rearward to collect over
the opening between the fourth and fifth legs and is from time to time
sucked in when the drop is big enough. Occasionally the pumping may
be strong enough to cause the water to overflow from the orbits on to the
back. This water too, collects at the opening between the fourth and fifth
legs. The apparent reticulation is the result of setae, regularly arranged
on small elevations with the distal ends of the setae clinging together.
Pumping of water up and out through the same exhalant opening is
commonly found among semi-terrestrial species of Metopograpsus ; M .
Zatifrons was seen by Verwey to lift the carapace in the same manner as
Sesarma. Some species of Macrophthalmus, Ilyoplax and Hetaplax,
when they are out of water, also show the pumping of water described
for Sesarma. The pumping of Metaplax crenulatus may be so strong that
occasionally one can see two small fountains spraying water up, to fall
over the back, on which the lines of the pattern lead the streams toward
the inhalant openings between the legs (Fig. 5 5 ) . Species of other
213
crab. His description was repeated by several authors, Ortmann (1901),
Bab&k (1921), Stebbing (1893) and by the compilers of the Cambridge
Natural History. Verwey (1930) elaborated the account having studied
S. mederi (= S. taeniolata), S. meinerti, S. bataviana and the freshwater
S. nodul-fera. The following account is from Verwey and has been
confirmed by undergraduate students working at Inhaca on S. meinerti.
When these species of Sesarma are immersed in water, it can be
demonstrated by the addition of carmine that water is taken in by way
of openings a t the base of the third maxillipeds (the so-called MilneEdwards opening), and also above the fourth and fifth walking legs,
and exhaled at the upper edge of the buccal cavity, When crabs
are in very shallow water the carapace may be raised to show above
the edge of the abdomen, a slit used for the uptake of a bubble of air
into the gill chamber. This process is usually rather one-sided, either
the right or the left side is raised. The musculature effecting this
movement has not been traced. Water is taken up from shallow
puddles by a different technique. The crab squats down so that the
Milne-Edwards opening is under water and Verwey has shown that
water is taken up during this period of squatting.
When the crabs are in shallow water or exposed to air, water is seen
to emerge from the exhalant opening and then to flow along three
grooves. Two of these lead directly to reticulated areas on the outer
surface of the branchiostegite, the other leads to the orbit and thence
by way of a narrow groove under the lateral margin of the back. These
streams of water flow over two apparently reticulated areas-that
flowing over a fronto-lateral area passes directly to the Milne-Edwards
opening ; that flowing over a lateral area passes rearward to collect over
the opening between the fourth and fifth legs and is from time to time
sucked in when the drop is big enough. Occasionally the pumping may
be strong enough to cause the water to overflow from the orbits on to the
back. This water too, collects at the opening between the fourth and fifth
legs. The apparent reticulation is the result of setae, regularly arranged
on small elevations with the distal ends of the setae clinging together.
Pumping of water up and out through the same exhalant opening is
commonly found among semi-terrestrial species of Metopograpsus ; M .
Zatifrons was seen by Verwey to lift the carapace in the same manner as
Sesarma. Some species of Macrophthalmus, Ilyoplax and Hetaplax,
when they are out of water, also show the pumping of water described
for Sesarma. The pumping of Metaplax crenulatus may be so strong that
occasionally one can see two small fountains spraying water up, to fall
over the back, on which the lines of the pattern lead the streams toward
the inhalant openings between the legs (Fig. 5 5 ) . Species of other