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 ARACHNIDA Remaining pairs of appendages similar in form and function, each tipped with two or three claws. Opisthosoma when segmented showing the same number of somites as in the Pedipalpi; usually unsegmented, the prse-genital somite constricted to form the waist; the appendages of its 3rd and 4th somites retained as spinning mammillae. Respiratory organs (see Fig. Q3,stg), as in the Amblypygi, or with the posterior pair, rarely the anterior pair as well, replaced by tracheal tubes. Intromittent organ of male in the apical segment of the 2nd prosomatic appendage. Sub-order a. Mesothelae (see Figs. 60 to 62).—Opisthosoma distinctly segmented, furnished with 11 tergal plates, as in the Amblypygi; the ventral surface of the 1st and 2nd somites with large sternal Fig. 61. —Liphistius desuitor. Ventral view with the prosomatic appendages cut short excepting the chelicer® (!) whose sharp retroverts are seen. Between the bases of the prosomatic limbs an anterior and a posterior sternal plate (black) are seen. 1, the sternum of the first opisthosomatic or genital somite covering the genital aperture and the first pair of lung-sacs. In front of it the narrow waist is formed by the soft sternal area of the prse-genital somite ; 2, the sternite of the second opisthosomatic somite covering the posterior pair of lungsacs ; 3 and 4, the spinning appendages (limbs) of the opisthosoma ; a, inner, f>, outer ramus of the appendage; 11, sternite of the eleventh somite of the opisthosoma: in front of it other rudimentary sternites; an, anus. (Original as above.) plates, covering the genital aperture and the two pairs of pulmonary sacs, the sternal plates from the 6th to the 11th somites represented by integumental ridges, weakly chitinized in the middle. The two pairs of spinning appendages retain their primitive position in the middle of the lower surface of the opisthosoma far in advance of the anus on the 3rd and 4th somites, each appendage consisting of a stout, many-jointed outer branch and a slender, unsegmented inner branch. Prosoma as in the Mygalomorphee, except that the mesosternal area is long and narrow. Family—Liphistiidse {LipMstius, *Arthrolycosa). Sub-order b. Opisthothelae (see Fig. 63). —Opisthosoma without trace of separate terga and sterna, the segmentation merely represented posteriorly by slight integumental folds and the sterna of the 1st and 2nd somites by the opercular plates of the pulmonary sacs. The spinning appendages migrate to the posterior end of the opisthosoma and take up a position close to the anus ; the inner branches of the anterior pair either atrophy or are represented homogenetically by a plate, the cribellum, or by an undivided membranous lobe, the colulus. Tribe 1. Mygalomorphse.—The plane of the articulation of the appendages of the 1st pair to the prosoma (the retro vert) vertical, the basal segment projecting straight forwards at its proximal end, the distal segment or fang closing backwards in a direction subparallel to the long axis of the body. Two pairs of pulmonary sacs.

Fig. 62.—Liphistius desuitor. Lateral view. I to VI, appendages of the prosoma cut off at the base ; o, ocular tubercle; prcegen, the pree-genital somite; 1 and 2, sternites of the first and second opisthosomatic somites; 3 and 4, appendages of the third and fourth opisthosomatic somites, which are the spinning organs, and in this genus occupy their primitive position instead of migrating to the anal region as in other spiders ; 5, tergite of the fifth opisthosomatic somite ; 11, eleventh opisthosomatic somite ; an, anus. (Original.) Families—Theraphosidse Pcecilotheria). Barychelidee (Barychelus, Plagiobothrus). Dipluridae (Diplura, Macrothele). Ctenizidse (Cteniza, Nemesia). Atypidse (Atypus, Calommata). Tribe 2. Arachnomorphse.—The plane of the articulation of the appendages of the 1st pair to the prosoma horizontal, the basal segment projecting vertically downwards, at least at its proximal end, the distal segment or fang closing inwards nearly or quite at right angles to the long axis of the body. The posterior pulmonary sacs (except in Hypochilus) replaced by tracheal tubes ; the anterior and posterior pairs replaced by tracheal tubes in the Capon iid;». Principal families—Hypochilidse (Hypochilus). Dysderidae (Dysdera, Segestria). Caponiid:e (C'opcuua, Nops). Filistatidie (FUistMa). Uloboridic (Uloborus, Dinopis). Argiapidae. (Nezphila, Gasteracantha). Pholcidse (Pholcus, Artema). Agelenidse (Tegenaria). Lycosidte

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(Lycosa). Clubionidse (Clubiona, Olios, Sparassus). Gnaphosidaa (Gnaphosa, Hemiclcea). Thomisidse (Thomisus). Attida: (Salticus). Urocteidae (Uroctea). Eresidse (Eresus). Rem,arks on the Aranece.—The Spiders are the most numerous and diversified group of the Arachnida; about 2000 species are known. No noteworthy fossil spiders are known ; the best preserved are in amber of Oligocene age. Protolycosa and Arthrolycosa occur in the Carboniferous. Morphologically, the spiders are

Fig. 63.—Ventral view of a male mygalomorphous Spider. I to VI, the six pairs of prosomatic appendages; a, copulatory apparatus of the second appendage ; 6, process of the fifth joint of the third appendage ; M, mouth ; pro, prosternite of the prosoma; mes, mesosternite of the prosoma: observe the contact of the cox® of the sixth pair of limbs behind it; compare Liphistius (Fig. 61) where this does not occur; stg, lung aperture; gn, genitalaperture; a,anus with a pair of backwardly migrated spinning appendages on each side of it; compare the position of these appendages in Liphistius (Fig. 61.) (From Lankester, “ Limulus an Arachnid.”)

remarkable for the concentration and specialization of their structure, which is accompanied with high physiological efficiency. The larger species of Bird’s Nest Spiders (Avicularia), the opisthosoma of which is as large as a bantam’s egg, undoubtedly attack young birds, and M ‘Cook gives an account of the capture in its web by an ordinary house spider of a small mouse. The “retrovert” or bent-back first pair of appendages is provided with a poison gland opening on the fang or terminal segment. Spiders form at least two kinds of constructions—snares for the capture of prey and nests for the preservation of the young. The latter are only formed by the female, which is a larger and more powerful animal than the male. Like the scorpions the spiders have a special tendency to cannibalism, and accordingly the male, in approaching the female for the purpose of fertilizing her, is liable to be fallen upon and sucked

Fig. 64.—Liphistius desuitor. Under side of the uplifted genital or first opisthosomatic somite of the female ; g, genital aperture; p, pitted plate, probably a gland for the secretion of adhesive material for the eggs ; l, th« edges of the lamell® of the lung-books of the first pair. (Original drawing by Pocock.) dry by the object of his attentions. The sperm is removed by the male from the genital aperture into a special receptacle on the terminal segment of the 2nd prosomatic appendage. Thus held out at some distance from the body, it is cautiously advanced by the male spider to the genital aperture of the female. For an account of the courtship and dancing of spiders, of their webs and floating lines, the reader is referred to the works of M‘Cook (30) and the Peckhams (31), whilst an excellent account of the nests of trap-door spiders is given by Moggridge (32). References to systematic works will also be found at the end of this article (33). Order 4. Palpigradi = Microthelyphonida (see Fig. 65).—Prosoma covered above by three plates, a larger representing the dorsal elements of the first four somites, and two smaller representing the dorsal elements of the 5th and 6th.