. Zoology : for students and general readers . Zoology. PLANARIAN WORMS. 143 body (Fig. 95, /), from which nerves pass in different directions, but a true nerve-cord is not known with cer- tainty to exist.* The eyes are very simple, indicated by two or more, sometimes thirty, dark pigment spots. In certain forms, such as Macrostomum, there is a ru- dimentary ear (otocyst). Most of the Planarians, land and aquatic, have organs of defence in the form of minute, stiff rods, either coiled up in an irregularly spiral manner, or short and straight, contained in oval cells. These bodies are shot out
. Zoology : for students and general readers . Zoology. PLANARIAN WORMS. 143 body (Fig. 95, /), from which nerves pass in different directions, but a true nerve-cord is not known with cer- tainty to exist.* The eyes are very simple, indicated by two or more, sometimes thirty, dark pigment spots. In certain forms, such as Macrostomum, there is a ru- dimentary ear (otocyst). Most of the Planarians, land and aquatic, have organs of defence in the form of minute, stiff rods, either coiled up in an irregularly spiral manner, or short and straight, contained in oval cells. These bodies are shot out in great numbers when the animals are irritated, but are not retractile, being pro- jected clear from the skin. In being neither retractile nor barbed, they differ from the lasso-cells of the jelly- fishes. That, however, they are true urticating organs has been proved by Mr. Thwaites (at the suggestion of Mr. Moseley), who, on •fnnpViino- pprf'iin OpvlnnpsiP «, male ' genltal-canal; *, oviducts; I, TOUCnmg cercam i^eyionchc eperm-sac; m, opening into the oviduct. land - planarians with his -AfterQuatrefages. tongue, felt an unpleasant tingling or scalding sensation, accompanied by a slight swelling. * Schmarda describes the nervous system of Bipalium dendropMlus as formed of two pairs of ganglia, from tlie hinder of which arise two par- allel nerve-threads, which dilate into at least nine swellings. Moseley discovered no more than one pair of ganglia in the species of Bipalium he examined. Blanchard has demonstrated "successive ganglionic repetitions along the nervous-threads at the right and left sides of the mid-line of the body of a large Planarian {Polydadus Oayi Blanch.). "— Clark's " Mind in Nature," p. Fisr. 9^.—Polycelis Imvigata. a, mouth ; b, buccal cavity ; c, (esophageal orifice ; d, stomach ; e, branclies of the stomach • /, lia ; g, testes ; A, vesiculae seminales ;. Please note that these images are extracted from scanned page
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectzoology, bookyear1879
