THE GULF-WEED CRAB

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It is said to be timid,

animals cast up by the waves. running off with great speed if scared, but if stopped it shows temper and nips hard. It is also very common, according to Lucas, in Algeria, where it is eaten by the poor. Fine specimens for a naturalist's collection are not easy to catch because of their extreme readiness on the least alarm to ensconce themselves deep in rifts of the rock. If in their headlong haste they sometimes slip into a hole too shallow to contain them entirely, the pursuer will still be likely only to obtain their cast-off legs, since they readily relinquish them all rather than be captured.

Nautilograpsus, Milne-Edwards, 1837, like some of the genera previously described, has third maxillipeds which do not form a complete operculum. In 1825, in Bowdich's 'Excursion to Madeira and Porto Santo,' Leach gave to this genus the name Planes, a wanderer, but from want of a sufficient accompanying description this has been regarded as technically only a manuscript name, not entitled to priority. It may, however, be doubted whether this is a right decision, since a figure of the type species, Planes minutus (Linn.), was appended, and there appears to be but a single species in the genus. The name of wanderer is very appropriate, since this, the common Gulf-weed Crab, is said to occur nearly everywhere on floating weed in the temperate and tropical seas of the globe. If, as is probable, it was the presence of this little crab on the Sargassum bacciferum that Columbus adduced as an argument to prove to his despairing sailors the proximity of land, it was not quite so much to the point as the sailors appear to have thought it. Columbus himself had other and more satisfactory reasons for his own confidence. Patrick Browne calls it the Turtle-Crab, remarking, 'I found this insect on the back of a turtle, near the western islands.'

Eriocheir, de Haan, 1835, meaning 'woolly-hand,' contains a species, Eriocheir japonicus, of very singular appearance, the great claws looking as if they were muffled up in cuffs of long fur. It is represented in the accompanying plate, which is reduced from de Haan's work.

The detached figures show the chelæ of the young male and the female, and the pleon respectively of male and female. By the Japanese this species is called the mountain savage or the hairy crab. It occupies brackish waters, passing from them into fresh-water streams, by means of which it ascends the mountains, where it is often observed on dry land.

Varuna, Milne-Edwards, 1830, has the single species Varuna litterata (Fabricius), common in the Indo-Pacific region, and attracting attention by the marking on the carapace to which the specific name refers. The capital letter H is here considered to be formed with more than usual distinctness by the longitudinal grooves that separate the lateral from the median regions, and the transverse groove which appears to form the upper boundary of the cardiac region.

Sesarma, Say, 1818, includes a large number of species found in the shallow waters of all the warm regions of the globe. In this genus the front' is broad; the third maxillipeds, when closed, still leave open a lozenge-shaped space, and have the large fourth joint traversed by a ridge from the front inner angle to the outer angle behind; the pterygostomian regions have a granular or reticulated surface, which in general is divided into little squares of extreme regularity.

Reference has been already made to Fritz Müller's investigation of the breathing arrangements in land-crabs. He was anxious to put the theory of evolution to a test. The resemblances which prevail among all crabs point, on that theory, to their derivation from a common ancestral form, but the differences which prevail in the numerous genera of land-crabs point to a divergence that must have begun long before they assumed terrestrial habits. That, at least, is what Fritz Müller assumes, and few evolutionists will be inclined to deny it. If, then, several different forms of water-breathers at various times and places have independently developed into air-breathers, it is unlikely that the necessary changes will all be of the same pattern. It is so unlikely that, had it proved to be the case, Fritz

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Müller was prepared to regard it as a very damaging blow to the theory of evolution. The result was just the opposite, as will be seen by a comparison of his observations on several species and genera. Those on Ocypode have been already quoted.

In the family Grapsida he describes, under the name Aratus Pisonii, the species which Milne-Edwards calls Sesarma Pisonii, a sweet little vivacious crab, which climbs the mangrove-bushes and feeds upon their leaves. Its short sharp claws are well fitted for climbing, but they prick like pins when the creature runs over a bare hand. Once, when he had one of these seated on his hand, Fritz Müller noticed that it raised up the hinder part of its carapace, and that by this means a wide slit was opened upon each side over the last pair of feet, affording a view into the branchial cavity. When studying this phenomenon in another species, which he took to be a true Grapsus, he observed that with the formation of the slit behind, the anterior part of the carapace seems to sink so as partly or entirely to close the anterior afferent opening. As the lifting of the carapace never takes place under water, he infers that the animal opens its branchial cavity in front or behind according as it requires to breathe water or air. He had noticed the elevation of the carapace, also, in species of Sesarma and Cyclograpsus, which burrow deep in swampy ground, and often scamper about on the wet mud, or sit watchfully before their burrows. But to observe the action in these is a work of patience, since they can continue to breathe water long after they have quitted the source of supply.

That reticulation of the shell between the afferent and efferent branchial orifices, which has been mentioned in the character of the genus Sesarma, has a special purpose. The squared meshes of network are due partly to fine tuberculation and partly to curious geniculate hairs forming over the surface a sort of fine hair-sieve. When the water issues from the branchial cavity it spreads through this network, and can take up fresh oxygen, whereupon the appendages of the third maxillipeds, working in the