Page:Encyclopædia Britannica, Ninth Edition, v. 6.djvu/689

Rh CRUSTACEA 655 class; 1 and the Scorpionidae should of course still form a part of the class Arachnida, which may, however, be conveniently placed beside the Crustacea, as in the annexed diagram (fig. 64), in which their probable morphological and ancestral relationship is indicated. TYPES OF EXISTING CRUSTACEA. Sub-class 1. THORACIPODA (or Malacostraca). I. PODOPHTHALMIA : (1.) DECAPODA (a) BKACHYURA. Crabs are certainly the highest representatives of the Crustacean class, and in this ten-footed order 2 are included some of the most active and intelligent members of the community, the &quot;land-crabs,&quot; and &quot;shore-crabs,&quot; and also the largest living representative of the class, the Inachus Kempferi from Japan. Crabs furnish the best illustration among the Crustacea of that concentration of organs around a single nerve- centre, which Professor Dana aptly terms cephalizatiori. Instead of a long vermiform body composed of a large number of annuli, each having its own nerve-ganglion, we have in the crab one large cephalo-thoracic ganglion repre senting nearly the entire nerve force of the body, the supra- 03sophageal ganglion only giving rise to the nerves of sense and volition. (See fig. 9, nerves of Maia. ) This highest cephalizecl type is exemplified by Maia, but as a matter of fact tho triangular crabs, of which Maia squinado and Inachus Kempferi are examples, do not embrace, by any means, the liveliest and most intelligent of the order ; on the contrary, we should decidedly award the highest place for intelligence to the quadrangular land and shore-crabs; indeed, it is amongst such genera as Grapsus, Gelasimus, Ocypoda, Gecarcinus, &c., that we find the most rapidly moving terrestrial forms of Crustacea. Most of the land-crabs retreat to burrows in the ground during the heat of the day, and issue forth at dusk to feed on the growing crops of sugar-cane, rice, or maize. The Gecarcinus ruricola (see ante, fig. 21) is peculiarly destruc tive to the young sugar-canes in the West Indies. In the highlands of the Deccan land-crabs are most abundant. Gecarcini are found at Mahableshwar at an elevation of 4500 feet above the sea. These land-crabs probably do not visit the sea at all, as do the Jamaica land-crabs, but de posit their eggs, when near the time of hatching, in the freshwater streams, the banks of which they are known to frequent. Many of the land-crabs have the chelate limbs largely developed, usually more strongly so in the males, e.g., the male of Macrophthalmus Latreillii ; in others one claw only is very disproportionately enlarged, as in the males of 1 In a paper on the structure of the Xiphosura and their relationship with the Eurypterida (Quart. Journ. Oeol. Soc., 1866, vol. xxiii. p. 85), the writer first suggested the probable genealogico-morphological rela tionship between Pterygotus and Scorpio ; and in a subsequent com munication (op. cit. 1871, p. 46) he combated the proposal of Dr Anton Dohrn to remove the Trilobita, Eurypterida, and Xiphosura from the Crustacea, and to combine them with Scorpio as a new class beside the Crustacea ; he also pointed out wherein the evidence relied upon by Dohrn for establishing such an order fails. The classification of the Eurypterida and Xiphosura proposed in his monograph (Pal. Soc. Mon. Merostomata, Pt. i.-iv., 1866-72) has been adopted by Pro fessors Owen and Huxley both, and has received the sanction of many eminent carcinologists. The writer has given his views as to the close affinity between the extinct Trilobita and the modern Isopoda in Brit. Assoc. Reports, Edinb., 1871, and Geol. Mag. 1871, vol. vm. p. 289, pi. 8. of which are distinguished by having their compound eyes placed on movable eye-stalks (hence called &quot;stalk-eyed Crustacea&quot;). They also have the gills covered by the carapace, forming, in fact, a more or less completely enclosed branchial chamber. Only one other Crustacean viz., Tanais (fig. 38), an Isopod, has such an arrangement in Tanais also the eyes are pedunculated. In Nebalia (2 in fig. 57), a Phyllopod, the eye is pedunculated, but in these instances the peduncle is not articulated. In the Trilobita several species occur with compound pedunculated eyes, but the eye-stalk has 110 articulus. the &quot; calling-crab&quot; (Gelasimus), which are said in running to carry this claw elevated as if beckoning with it. Fritz Miiller says, however, that the species common in Brazil (a small Gelasitmis with one claw very large) always holds it FIG 65. The &quot; Calling-dab&quot; (Gelasimus), $ a land-crab common In the cassava- fields, Brazil. closely pressed against, its body. Vast numbers of land- crabs are met with on the sea-shore and among rocks along the coast, especially in the wanner temperate and sub-tropi cal regions of the earth. Of the genus Thelphusa one freshwater species ( T. jluviatilis) is a native of the rivers of southern Europe. It is eaten by Catholics during Lent, and hence called &quot; Lenten crab.&quot; This crab is also common to the rivers of India. Although some land-crabs are certainly vegetarians in diet, the class, as a whole, are carrion feeders, greedily devouring animal matter even in a putrescent state. The Portunidae and Carcinidce perform the duties of sanitary police around our coasts between tide-marks, being assisted by swarms of &quot;sand-hoppers&quot; (Talitrus locusta] ; whilst below low-water mark the prawns, Maias, great crabs, and lobsters share the task. Many sea-side resorts would bo extremely unwholesome were it not for the labours of these useful but unpaid scavengers. The swimming-crabs are mostly predaceous; forms like Portunus pelagicus and Polybius Henslowii (ng. 66) have exceedingly thin shells, and all the feet, save the great chelate claws, are modified into oars. They are thus en abled to live and hunt at their ease, often hundreds of miles from land. The writer has seen Henslow s swimming-crab in the middle of the FIG. 66. HenslowsSwimminR-crab./ &amp;gt; 3^i ws//cns/o-f?. -P.- .&amp;lt; Leach, coast of Cornwall. Bay of Biscay tar out of sight of land. Crouch, the Cornish naturalist, states that they fasten upon pilchards and mackerel with their knife-like claws, and never relax their hold until the ter rified victim floats exhausted on the surface. Two genera of Tertiary Land-crabs have been described from English localities (Goniocypoda? and Litoricola).* Macrophthalmus occurs fossil in China, where it is prized as a valuable materies medical Ranina,&quot; the frog-crab &quot; of the Indian Ocean and Japan, occurs in Tertiary rocks 6 in Bunde and Ebenda, Germany, in San Stefano, Italy, and 3 Goniocypoda Edwardsii, H. Woodw., L. Eocene High Cliff, Hampshire Oeol. Mag., 1867, vol. iv. pi. 21. fig. 1, p. 529. Eocene, Portsmouth, Quart. Journ. Geol. Soc., vol. xxix pi. 2, P- M 5 Notes on Chinese Materia Medico, by D. Hanbury, F.L.b., l fu dJiDd Salter s Chart of the Fossil Cnistacca, engraved by J. W. Lowry ; Stanfords, Charing Cross, 1865.
 * The crabs belong to the legion Podophthalmia, all the members
 * Litoricola glabra, H. Woodw., and L. dentata, H. Woodw., U