ARACHNIDA mammal) with the large chelae brings its tail over its head, and deliberately punctures the struggling victim twice with its sting (Fig. 52). The poison of the sting is similar to snake-poison (Calmette), and rapidly paralyses animals which are not immune to it. It is probably only sickly adults or young children of the human race who can he actually killed by a scorpion’s sting. When the scorpion has paralysed its prey in this way, the two short chelicera? are brought into play (Fig. 53). By the crushing action of their pincers, and an alternate backward and forward movement, they bring the soft blood-holding tissues of the victim close to the minute pin-hole aperture which is the scorpion’s mouth. The muscles acting on the bulb-like pharynx now set up a pumping action (see Huxley, 26); and the juices*—but no solid matter, excepting such as is reduced to powder—are sucked into the scorpion’s alimentary canal. A scorpion appears to prefer for its food another scorpion, and will suck out the juices of an individual as large as itself. When this has taken place, the gorged scorpion becomes distended and tense in Pio. 52.—Drawing from life of the Italian the mesosomatic region. It Scorpion Euscorpius italicus, Herbst, is certain that the absorbed holding a blue-bottle fly with its left ■ { d _ t chela, and carefully piercing it between J , . . rv , th, ali head and thorax with its sting. Two mentary canal alone, but pass insertions of the sting are effected and also into its csecal off-sets, the fly is instantly paralysed by the ducts of the poison so introduced into its body. which , . are , ithe/ oox (From Lankester, Journ. Linn. Soc.) gastric glands (see rig. 33). All Arachnida, including Limulus, feed by suctorial action in essentially the same way as Scorpio. Scorpions of various species have been observed to make a hissing noise when disturbed, or even when not disturbed. The sound is produced by stridulating organs developed on the basal joints of the limbs, which differ in position and character in different genera (see Pocock, 27). Scorpions copulate with the ventral surfaces in contact. The eggs are fertilized, practically in the ovary, and develop in situ. The young are born fully formed and are carried by the mother on her back. As many as thirty have been counted in a brood. For information as to the embryology of scorpions, the reader is referred to the works named in the bibliography below. Scorpions do not possess spinning organs nor form either snares or nests, so far as is known. But some species inhabiting sandy deserts form extensive burrows. The fifth pair of prosomatic appendages is used by these scorpions when burrowing, to kick back the sand as the burrow is excavated by the great chelae. References to works dealing with the taxonomy and geographical distribution of scorpions are given at the end of this article (28). Section /3. Epedinata.—The primitive distinction between the mesosoma and the metasoma wholly or almost wholly obliterated, the two regions uniting to form an opisthosoma, which never consists of more than twelve somites and never bears appendages or breathing-organs behind the 4th somite. The breathing-organs of the opisthosoma, when present, represented by two pairs of stigmata, opening either upon the 1st and 2nd (Pedipalpi) or the 2nd and 3rd somites (Solifugse, Pseudo-scorpiones), or by a single pair upon the 3rd (? 2nd) somite (Opiliones) of the opisthosoma, there being rarely an additional stigma on the 4th (some Solifugse). The appendages of the 2nd somite of the opisthosoma absent, rarely minute and budlike (some Amblypygi), never pectiniform. A prae-genital somite is often present either in a reduced condition forming a waist (Pedipalpi, Aranese, Palpigradi) or as a full - sized tergal plate (Pseudo-scorpiones) ; in some it is entirely atrophied (Solifugse, Holo- Fig. 53.—The same Scorpion somata, and Rhynchostomi). Lateral carrying the now paralysed fly held in its chelicera;, the eyes when present diplostichous. chelae liberated for attack and Remarks.—The Epectinate Arachnids defence. Drawn from life. do not stand so close to the aquatic (From Lankester,/owm.Lma. ancestors of the Embolobranchia as do Soc..) the Pectiniferous scorpions. At the same time we are not justified in supposing that the scorpions stand in any way as an intermediate grade between any of the existing Epectinata and the Delobranchia. It is probable that the Pedipalpi, Aranese, and Podogona have been separately evolved as distinct lines of descent from the ancient aquatic Arachnida. The Holosomata and Rhynchostomi are probably off-shoots from the stem of the Aranese, and it is not unlikely (in view of the
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structure of the prosomatic somites of the Tartarides) that the Solifugse are connected in origin with the Pedipalpi. The appearance of tracheae in place of lung-sacs cannot be regarded as a starting-point for a new line of descent comprising all the tracheate forms ; tracheae seem to have developed independently in different lines of descent. On the whole, the Epectinata are highly specialized and degenerate forms, though there are few, if any, animals which surpass the spiders in rapidity of movement, deadliness of attack, and constructive instincts. Order 2. Pedipalpi (Figures 54 to 59).—Appendages of 1st pair bisegmented, without poison gland ; of 2nd pair prehensile, their basal segments underlying the proboscis, and furnished with
Fig. 54.—Thelyphonus, one of the Pedipalpi. A, ventral view; I, chelicera (detached); II, chehe ; III, palpiform limb; IV to 1VI, the walking legs ; stc, sterno-coxal process (gnathobase) of the chelae; si , anterior sternal plate of the prosoma ; s<2, posterior sternal plate of the prosoma ; pregen, position of the prae-genital somite (not seen); l, l, position of the two pulmonary sacs of the right side ; 1 to 11, somites of the opisthosoma (mesosoma plus metasoma) ; msg, stigmata of the tergo-stemal muscles ; an, anus. B, dorsal view of the opisthosoma of the same ; pregen, the prae-genital somite ; p, the tergal stigmata of the tergo-sternal muscles; paf, post-anal segmented filament corresponding to the post-anal spine of Limulus. (From Lankester, Q. J. Mic. Sci. N.S. vol. xxi. 1881.) sterno-coxal (maxillary) process, the apical segment tipped with a single movable or immovable claw ; appendages of 3rd pair different from the remainder, tactile in function, with at least the apical segment many-jointed and clawless. The ventral surface of the prosoma bears prosternal, metasternal, and usually mesosternal chitine-plates (Fig. 55). A narrow prse-genital somite is present between opisthosoma and prosoma (Figs. 55, 57). Opisthosoma consisting of eleven somites, almost wholly without visible appendages. Intromittent organ of male beneath the genital operculum (= sternum of the 1st somite of opisthosoma).
Fig. 55.—Thelyphonus sp. Ventral view of the anterior portion of the body to show the three prosomatic sternal plates a, h, c, and the rudimentary sternal element of the prse - genital somite ; opisth 1, first somite of the opisthosoma. (From a drawing made by Mr. PickardCambridge, under the direction of Mr. R. I. Pocock.)
Note. — The possibility of another interpretation of the anterior somites of the mesosoma and the prae-genital somite must be borne in mind. Possibly, though not probably, the somites carrying the two lung-sacs correspond to the first two lung-bearing somites of Scorpio, and it is the genital opening which has shifted. The same caution applies in the case of the Aranese. Excalation of one or of two anterior mesosomatic somites, besides the prse-
