. Elementary text-book of zoology. Zoology. 344 NEMATHELMIXTHES. phala they are branching subcutaneous canals. With a few excep- tions the Nematheltninthes have separated sexes, and develop directly without metamorphosis. The larvae and sexual animals are not unfrequently distributed in two different hosts. The majority of the Nemathelminthes are parasites either during the whole period of their life or at different stages. There are, however, also free living forms which often show the closest relationship to the parasitic members of the group. Order 1.—NEMATODA (THREAD-WORMS).* Nemathelminth
. Elementary text-book of zoology. Zoology. 344 NEMATHELMIXTHES. phala they are branching subcutaneous canals. With a few excep- tions the Nematheltninthes have separated sexes, and develop directly without metamorphosis. The larvae and sexual animals are not unfrequently distributed in two different hosts. The majority of the Nemathelminthes are parasites either during the whole period of their life or at different stages. There are, however, also free living forms which often show the closest relationship to the parasitic members of the group. Order 1.—NEMATODA (THREAD-WORMS).* Nemathelminthes, with mouth and ali- mentary canal. They are principally parasites. The Nematodes possess an extremely elongated thread-like body, which may be provided with papillae at the anterior pole in the region of the mouth, or with hooks and spines within the oral cavity. The mouth leads into a narrow oesophagus, which usually has thick muscular walls, a chitinous lining, and a triangular lumen, and is frequently dilated behind to a muscular bulb (pharynx). In certain genera (Shabditis, Oxyuris], the chitinous lining of the pharynx is raised into ridges or tooth-like prominences, to which the * Besides the older writings of Rudolphi. Bremser, Cloquet, Dujardin. compare Diesing, " Systema helminthum," 2 Bde Wien, Diesing, " Eevision der Nematoden," Wimcr Sitziint/xbrricJitt', 1860. Claparede, •'De la for- mation et de la fecondation des ceufs ehez les vers Nematodes," Geneve, 1856. A. Schneider. "Monographic der Nematoden," Berlin. 186ii. R. Leuckart, " Untersuchimgen iiber Trichina spiralis," Leipzig and Heidelberg, 1866, 2nd edition; also " Die menschlichen ; etc., Tom. II., Leipzig and Heidelberg, 1876. C. Claus, li Ueber Leptodera appeudicnlata," Marburg. 1868. 0. Butschli, '• Untersuchungen iiber die beiden Nematoden der Periplaucta orieiitalis," ZeitzscJtr. fiir H'/. Zool., Tom. XXI.,
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1884
