. Outlines of zoology. nce is very short, spiders trusting mostto their exquisite sense of touch, by which they discriminate SPIDERS. 369 the various vibrations on a web line. The senses of smell,hearing, and taste are also present, but little is known the organs. Body cavity, endosternite, and coxal glands generallyresemble those of scorpions. The spider usually sucks theblood and juices of its prey,and beliind the gullet liesa powerfully suctorial region,strengthened by chitinousplates, and worked by the small mid-gut arisefive pairs of long cssca, a pairrunning forw
. Outlines of zoology. nce is very short, spiders trusting mostto their exquisite sense of touch, by which they discriminate SPIDERS. 369 the various vibrations on a web line. The senses of smell,hearing, and taste are also present, but little is known the organs. Body cavity, endosternite, and coxal glands generallyresemble those of scorpions. The spider usually sucks theblood and juices of its prey,and beliind the gullet liesa powerfully suctorial region,strengthened by chitinousplates, and worked by the small mid-gut arisefive pairs of long cssca, a pairrunning forwards and a pairpassing into the bases of eachpair of legs, and then backagain. These cseca sometimesanastomose. Farther back themid-gut gives off numerousdigestive outgrowths, which filla large part of the secretion digests pro-teids. Terminally there is alarge cloaca, and where theintestine joins this, four much-branched excretory Malpighiantubes are given off, which are fig. 193.—Dissection, of ^i-a/d. said toorigin. be endodermal in from the ventral surface.—AfterCuvier. Chelicerae ; 2, pedipalps cut short;3-6, walking legs ; ^.1, large thoracicganglion; gfi^ ganglion at base ofabdomen; , chambered tracheaeor lung-books—at the left side theanterior is cut open to show thelamellae (/.); w., muscle of abdomen;st.^ and stJ^, stigmata of lung-books;ov., ovary ; sp., spinnerets. A three-chambered heart,containing colourless blood,lies within a pericardium nearthe dorsal surface of theabdomen. It gives off ananterior and a posterior aortaand lateral vessels; and thecirculation corresponds in general to that of the scorpion. In a few forms (Tetrapneumones) respiration is effected by four lung-books, in the large bird-catching My gale (Fig. 193). In the vast majority (Dipneumones) there are two lung-books, and tubular tracheae in addition. The 24 37° PHYLUM ARTHROPODA. Stigmata of the lung-books lie on the anterior ventral surfaceof the abdomen; the tra
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Keywords: ., bookcentury1900, bookdecade1910, bookidcu3192, booksubjectzoology
