rest.


CHAPTER 5. RESPIRATION IN LAND CRABS.

Among the numerous facts in the natural history of the Crustacea upon
which a new and clear light is thrown by Darwin's theory, besides the
two forms of the males in our Tanais and in Orchestia Darwinii, there is
one which appears to me of particular importance, namely, the character
of the branchial cavity in the air-breathing Crabs, of which,
unfortunately, I have been unable to investigate some of the most
remarkable (Gecarcinus, Ranina). As this character, namely, the
existence of an entrance behind the branchiae, has hitherto been
noticed, even as a fact, only in Ranina, I will go into it in some
detail. I have already mentioned that, as indeed is required by Darwin's
theory, this entrant orifice is produced in different manners in the
different families.

In the Frog-crab (Ranina) of the Indian Ocean, which, according to
Rumphius, loves to climb up on the roofs of the houses, the ordinary
anterior entrant orifice is entirely wanting according to Milne-Edwards,
and the entrance of a canal opening into the hindmost parts of the
branchial cavity is situated beneath the commencement of the abdomen.

The case is most simple in some of the Grapsoidae, as in Aratus Pisonii,
a charming, lively Crab which ascends the mangrove bushes (Rhizophora)
and gnaws their leaves. By means of its short but remarkably acute
claws, which prick like pins when it runs over the hand, this Crab
climbs with the greatest agility upon the thinnest twigs. Once, when I
had one of these animals sitting upon my hand, I noticed that it