Lectures on the comparative anatomy and physiology of the invertebrate animals : delivered at the Royal College of Surgeons . tracting the air from the water. The spiders of the genera Segestria and Dysdera have four stig-mata, situated on the under and anterior part of the abdomen : theanterior one on each side {Jig- 168, a)is the aperture of the pulmonary sac (6);the lower orifice (c) leads to a short andwide cylinder, from which radiate nume-rous tracheae (c?) having the usual shiningsurface. These tubes are united togetherin bundles, and diverge to the surround-ing parts by dissociation, n
Lectures on the comparative anatomy and physiology of the invertebrate animals : delivered at the Royal College of Surgeons . tracting the air from the water. The spiders of the genera Segestria and Dysdera have four stig-mata, situated on the under and anterior part of the abdomen : theanterior one on each side {Jig- 168, a)is the aperture of the pulmonary sac (6);the lower orifice (c) leads to a short andwide cylinder, from which radiate nume-rous tracheae (c?) having the usual shiningsurface. These tubes are united togetherin bundles, and diverge to the surround-ing parts by dissociation, not by trueramification, like the tracheae of mitesand insects. One bundle is dispersedthroughout the abdomen ; another entersthe cephalothorax and resolves itselfinto groups corresponding in numberwith the limbs to the extremity of Avhichthe fine silvery tracheae can be Epeira and some other spiders thereis a transverse fissure in front of the spin-nerets, from which a short tracheal trunkproceeds : this sends off four simple flat-tened tracheae, devoid of the spiral filament, which extend, gradually G G 4 168. Respiratory organs, Stgestria 456 LECTURE XIX. attenuating to the base of the abdomen.* The pulnaonary sac ^, 170, h\ which receives the air by the anterior respiratory ori-fice, is of an elliptical form ; the vascular surface is augmented by anumber of broad and close-set lamellae which project into its interior. In the scorpion {^fig. 164), the stigmata or pulmonary orifices areeight in number, four on each side of the under surface of the an-terior broad segments of the abdomen (1, 2, 3, 4). They havethe form of oblique fissures, surrounded by a thickened margin, towhich tlie name of peritrema has been given. The vascular liningmembrane of the cavity adheres to this margin, and is at firstsimple, but afterwards gives attachment to a series of twentybroad and close-set lamellag, arranged, as in the spiders, like theleaves of a book. The genus Phrynus
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Keywords: ., bookauthorowenrichard18041892, bookcentury1800, bookdecade1850
