Outlines of zoology . noderms. — This is a well-defined series, including star-fishes,brittle-stars, sea-urchins, sea-cucum-bers, and feather - stars. Thesymmetry of the adult is usuallyradial, though that of the larva isbilateral. A peculiar system, knownas the water - vascular system, ischaracteristic, and is turned to various uses, as inlocomotion and respiration. There is a marked tend-ency to deposition of lime in the tissues. The develop-ment is strangely circuitous or indirect. Segmented worms.—It is hopeless atpresent to arrange withany definiteness thoseheterogeneous forms towhich the
Outlines of zoology . noderms. — This is a well-defined series, including star-fishes,brittle-stars, sea-urchins, sea-cucum-bers, and feather - stars. Thesymmetry of the adult is usuallyradial, though that of the larva isbilateral. A peculiar system, knownas the water - vascular system, ischaracteristic, and is turned to various uses, as inlocomotion and respiration. There is a marked tend-ency to deposition of lime in the tissues. The develop-ment is strangely circuitous or indirect. Segmented worms.—It is hopeless atpresent to arrange withany definiteness thoseheterogeneous forms towhich the title worm is given. For this titleis little more than aname for a shape,assumed by animals ofvaried nature who be-gan to move headforemost and to acquiresides. There is noclass of worms, butan assemblage—a mob—not yet reduced toorder. It seems useful, however, to separate those whichare ringed or segmented from those which are former are often called Annelids, and include two chiefclasses:—. Fig. 13.—Crinoid or feather-star. UNSEGMENTED WORMS. (i) Chaetopoda or Bristle-footed worms, lob-worm ; and (2) Hirudinea or Leeches. earthworm.
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Keywords: ., bookcentury1900, bookdecade1910, bookidcu3192, booksubjectzoology
