elevated the hinder part of its carapace, and that by this means a wide
fissure was opened upon each side above the last pair of feet, through
which I could look far into the branchial cavity. I have since been
unable to procure this remarkable animal again, but on the other hand, I
have frequently repeated the same observation upon another animal of the
same family (apparently a true Grapsus), which lives abundantly upon the
rocks of our coast. Whilst the hinder part of the carapace rises and the
above-mentioned fissure is formed, the anterior part seems to sink, and
to narrow or entirely close the anterior entrant orifice. Under water
the elevation of the carapace never takes place. The animal therefore
opens its branchial cavity in front or behind, according as it has to
breathe water or air. How the elevation of the carapace is effected I do
not know, but I believe that a membranous sac, which extends from the
body cavity far into the branchial cavity beneath the hinder part of the
carapace, is inflated by the impulsion of the fluids of the body, and
the carapace is thereby raised.

I have also observed the same elevation of the carapace in some species
of the allied genera Sesarma and Cyclograpsus, which dig deep holes in
marshy ground, and often run about upon the wet mud, or sit, as if
keeping watch, before their burrows. One must, however, wait for a long
time with these animals, when taken out of the water, before they open
their branchial cavity to the air, for they possess a wonderful
arrangement, by means of which they can continue to breathe water for
some time when out of the water. The orifices for the egress of the
water which has served for respiration, are situated in these, as in
most Crabs, in the anterior angles of the buccal frame ("cadre buccal,"
M.-Edw.), whilst the entrant fissures of the branchial cavity extend
from its hinder angles above the first pair of feet. Now that portion of
the carapace which extends at the sides of the mouth between the two