. Evenings at the microscope : or, Researches among the minuter organs and forms of animal life . Zoology; Microscopy; Microscopes. 206 EVENINGS AT THE MICEOSCOPE. joint are permeated by a slender membranous tube, which is the poison duct, and which terminates at the open extremity of the former, while at the other end it commu- nicates with a lengthened oval sac where the venom is secreted. This, of course, we do not see here, for it is not sloughed with the exuviae, but retained in the interior of the body; but in life it is a sac, extending into the cephalo-thorax,—as that part of the body

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. Evenings at the microscope : or, Researches among the minuter organs and forms of animal life . Zoology; Microscopy; Microscopes. 206 EVENINGS AT THE MICEOSCOPE. joint are permeated by a slender membranous tube, which is the poison duct, and which terminates at the open extremity of the former, while at the other end it commu- nicates with a lengthened oval sac where the venom is secreted. This, of course, we do not see here, for it is not sloughed with the exuviae, but retained in the interior of the body; but in life it is a sac, extending into the cephalo-thorax,—as that part of the body which carries the legs is called,—and covered with spiral folds pro- duced by the arrangement of the fibres of its contractile tissue. "When the Spider attacks a fly, it plunges into its victim the two fangs, the action of which is downwards, and not from right to left, like that of the jaws of insects. At the same instant a drop of poison is secreted in each gland, which, oozing through the duct, escapes from the perforated end of the fang into the wound, and rapidly produces death. The fangs are then clasped down, carrying the prey, which they powerfully press against the toothed fang of bpideh. edges of the stout basal piece, by which means the nutritive fluids of the prey are pressed out, and taken into the mouth, the dried and empty skin being rejected. The poison is of an acid nature, as experiments performed with irritated spiders prove ; litmus paper pierced by them becoming red as far round the perforations as the emitted fluid spreads. In the slough, the upper surface of the cephalo-thorax is always detached as a thin plate, convex outwardly, con- cave inwardly. As it is upon the front portion of this division of the body that the eyes are situate, the slough displays these with great clearness and beauty beneath the microscope. Here you may see them. The whole slough. Please note that these images are extracted from scanned page images that may have been dig

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