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ARAOHNIDA

segments of the 5th and 6th pairs of prosomatic appendages. Lateral eyes, when present, represented by separate ocelli. The prse-genital somite, after appearing in the embryo, either is obliterated (Scorpio, Galeodes, Opilio, and others) or is ictained as a reduced narrow region of the body, the “ waist, between prosoma and mesosoma. It is represented by a full-sized tergal plate in the Pseudo-scorpiones. Section a. Pedinifera.—The primitive distinction between the mesosoma and the metasoma retained, the latter consisting of six somites and the former of six somites in the adult, each oi which is furnished during growth with a pair of appendages. Including the prse-genital somite (Fig. 16), which is suppressed in the adult, there are thirteen somites behind the prosoma. The appendages of the 1st and 2nd mesosomatic somites persisting as the genital operculum and pectones respectively, those of the 3rd, 4th, 5th, and 6th somites (? in Palceophonus) sinking below the surface during growth in connexion with the formation of the four pairs of pulmonary sacs (see Fig. 17). Lateral eyes monostichous. Order 1. Scorpionidea.—Prosoma covered by a single dorsal shield, bearing typically median and lateral eyes; its sternal elements reduced to a single plate lodged between or behind the basal segments of the 5th and 6th pairs of appendages. Appendages of 1st pair tri-segmented, chelate ; of 2nd pair chelate, with their basal segments subserving mastication ; of 3rd, 4th, 5th, and 6th pairs similar in form and function, except that in recent

’ig. 49.—Ventral view of a restoration of Palceophonus Hunteri, Pocock, the Silurian Scorpion from Lesmahago, Scotland. Restored by Mr. R. I. Pocock. The meeting of the coxse of all the prosomatic limbs in front of the pentagonal sternum ; the space for a genital operculum ; the pair of pectens, and the absence of any evidence of pulmonary stigmata are noticeable in this specimen. (See Pocock, Quart. Jour. Micr. Sci. 1901.)

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and Carboniferous forms the basal segments of the 3rd and 4th are provided with sterno-coxal (maxillary) lobes, those of the 4th pair meeting in the middle line and underlying the mouth. The live posterior somites of the metasoma constricted to form a “ tail,” the post-anal sclerite persisting as a weapon of offence and provided with a pair of poison glands (see Figs. 8, 10, 12, 13, 14, 15, 21, and 22). Sub-order Apoxypoda.—The 3rd, 4th, 5th, and 6th pairs of appendages short, stout, tapering, the segments about as wide as long, except the apical, which is distally slender, pointed, slightly curved, and without distinct movable claws. Family—Pabeophonidae, Pakeophonus (Figs. 48 and 49). Sub-order Dionychopoda.—The 3rd, 4th, 5th, and 6th pairs of appendages slender, not evenly tapering, the segments longer than wide; the apical segment short, distally truncate, and provided with a pair of movable claws. Basal segments of the 5th and 6th pairs of appendages abutting against the sternum of the prosoma (see Fig. 10 and Figs. 51, 52, and 53). Family—Pandinidae {Patxdinus, Opisthophthalmus, Urodacus). ,, Yejovidse (Kcejovis, Jurus, Euscorpius, Broteas). ,, Bothriuridse (Bothriurus, Cercophonius). ,, Buthidae {ButJms, Centrums). ,, Carbon,, Remarks on the Order Scorpionidea. —The Scorpion is one of the great animals of ancient lore and tradition. It and the crab are the only two invertebrates which had impressed the minds of early men sufficiently to be raised to the dignity of astronomical representation. It is all the more remarkable that the scorpion proves to be the oldest animal form of high elaboration which has persisted to the present day. In the Upper Silurian two specimens of a scorpion have been found (Figs. 48, 49), one in Gothland and one in Scotland, which would be recognized at once as true
 * Cyclophthalmidae (Cydophthalmus)
 * Eoscorpiidae (i?oscorpws, Centromachus J iferous.

scorpions by a child or a savage. The Silurian scorpion, Ralocophonus, differs, so far as obvious points are concerned, from a modern scorpion only in the thickness oi its legs and in their terminating in strong spike-like joints, instead of being slight and provided with a pair of terminal claws. The legs of the modern scorpion (Fig. 10 : Fig. 51) are those of a terrestrial Arthropod, such as a beetle ; whilst those of the Silurian scorpion are the legs of an aquatic Arthropod, such as a crab or lobster. It is probable that Pig. 50.—Comparison of the sixth prosomatie limb of a recent Scorpion (B), of Palseophonus (C), and of Limulus(A), showing their agreement in the number of segments ; in the existence of a movable spine, Sp, at the distal border of the fifth segment; in the correspondence of the two claws at the free end of the limb of Scorpio with two spines similarly placed in Limulus ; and, lastly, in the correspondence of the three talonlike spines carried on the distal margin of segment six of recent Scorpions with the lour larger but similarly situated spines on the leg of Limulus; s, groove dividing the ankylosed segments 4 and 5 of the Limulus leg into two. (After Pocock, Q. J. Mic. Sci. 1901.)

the Silurian scorpion was an aquatic animal, and that its respiratory lamellse were still projecting from the surface of the body to serve as branchke. No trace of “stigmata,” the orifices of the lungchambers of modern scorpions, can be found in the Scottish specimen of Palteophonus, which presents the ventral surface of the animal to view. On the other hand, no trace of respiratory appendages excepting the pectens can be detected in the specimen (see Fig. 49). Fossil scorpions of the modern type are found in the Coal Measures. At the present day scorpions of various genera are found in all the warm regions of the world. In Europe they occur as far north as Bavaria and the south of France. The largest species measure

•pIG Drawirw from life of the desert Scorpion, Buthus australis, Lin.,. from Biskra, N.”Africa. (From Lankester, Journ. Linn. Soc. Zool. vol. xvi. 1881.) 9 inches from the front of the head to the end of the sting, and occur in tropical India and Africa. Between 200 and 300 species are known. The scorpions use their large chelae for seizing prey and for fighting with one another. They never use the sting when (as frequently happens) they attack another scorpion, because, as was ascertained by A. G. Bourne (24), the poison exuded by the sting has no injurious effect on another scorpion nor on the scorpion itself. The stories of a scorpion stinging itself to death when placed in a circle of burnin coals are due to erroneous observation. When placed in such position thescorpion faints and becomes inert. It is found (Bourne, 24) that some species of scorpion faint at a temperature of 40° cent. They recover on being* removed to cooler conditions. A scorpion having seized its prey (usually a large insect, or small reptile or