Lectures on the comparative anatomy and physiology of the invertebrate animals : delivered at the Royal College of Surgeons . ous fluid are lodged in that well-known pyriform dilatationformed by the last joint of the tail, and which is terminated by theslender, sharp, recurved sting.*] A minute slitmay be observed near the point, which is thecommon outlet of two slender ducts, that gra-dually dilate into two secreting sacs, lodged inthe cavity of the expanded part of the joint,and separated from each other by a double ver-tical partition. Their chief tunic is formed bya layer of smooth muscula
Lectures on the comparative anatomy and physiology of the invertebrate animals : delivered at the Royal College of Surgeons . ous fluid are lodged in that well-known pyriform dilatationformed by the last joint of the tail, and which is terminated by theslender, sharp, recurved sting.*] A minute slitmay be observed near the point, which is thecommon outlet of two slender ducts, that gra-dually dilate into two secreting sacs, lodged inthe cavity of the expanded part of the joint,and separated from each other by a double ver-tical partition. Their chief tunic is formed bya layer of smooth muscular fibres, external towhich is a stratum of cylindrical cells. The poison-apparatus of spiders is placed atthe opposite extremity of the body. The perfo-rated sting or fang forms the second joint of themandible or modified antenna, upon which ithas a gynglymoid movement, and lies concealedand protected, when not in use, in a furrow withdentated margins upon the basal joint {, mf). The poison gland {fig. 169, a) is an elongated ovoid vesicle,the exterior of which is characterised by spiral folds produced by the 169. Mygale. * XXIV. p. 535. t Prep. No. 2161. ARACHNIDA. 4o7 arrangement of the fibres of the contractile tunic. The duct (b) tra-verses the basal joint of the mandible and the cavity of the fang (c),and terminates in a fissure on its convex surface near the point. Inthe true Aranece, the Clubiones, and the Lycozw, the poison glandsextend into the cephalothorax ; but in the bird-spiders {Mygale)they are limited to the mandibles. It is probable, therefore, thatthe effects of a Avound occasioned by these gigantic spiders may beexaggerated: those species of our native spiders, which are most for-midably armed, cause little or no inflammation in piercing the humanskin ; but their poison seems to take fatal effect upon insects. Themechanical laceration, and the sucking out their juices, must, how-ever, be taken into the account of the lethal powers of the spidersasexerc
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