. Outlines of zoology. Zoology. Fig. 14.—Earthworm. Chsetopoda or Bristle-footed worms, earthworm and lob-worm; and Hirudinea or Leeches ; and some smaller classes. Unsegmented " ;—These differ from the higher " worms " in the absence of true segments and appendages, and resemble them in their bilateral symmetry. The series includes Turbellarians or Planarians; the parasitic Tre- matodes or Flukes; the parasitic Cestodes or Tape-worms; the Nemerteans or Ribbon-worms; the frequently, parasitic Nema- todes or Thread-worms; and several smaller classes. As to certai
. Outlines of zoology. Zoology. Fig. 14.—Earthworm. Chsetopoda or Bristle-footed worms, earthworm and lob-worm; and Hirudinea or Leeches ; and some smaller classes. Unsegmented " ;—These differ from the higher " worms " in the absence of true segments and appendages, and resemble them in their bilateral symmetry. The series includes Turbellarians or Planarians; the parasitic Tre- matodes or Flukes; the parasitic Cestodes or Tape-worms; the Nemerteans or Ribbon-worms; the frequently, parasitic Nema- todes or Thread-worms; and several smaller classes. As to certain other forms, such as the sea-mats (Polyzoa or Bryozoa), the lamp-shells (Brachiopoda), and the worm- like Sipunculids, it seems best, at this stage, to confess that they are incertcz sedis. But the general fact is not without interest, that in the midst of the well-defined classes of Invertebrates there lies, as it were, a pool from which many streams of life have flowed; for among the heterogeneous " worms " we detect affinities with Arthropods, Molluscs, Echinoderms, and even Vertebrates. At this stage we may notice that in all the above forms the typical symmetry is bilateral (see p. 33) (in Echinoderms, the radial symmetry. Fig. 15.—Bladderworm stage of a Cestode.—After Leuckart. a, Early stage with head inverted. £, Later stage with head Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Thomson, J. Arthur (John Arthur), 1861-1933. Edinburgh, Glasgow and London, H. Frowde and Hodder & Stoughton
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Keywords: ., bookauthorth, bookcentury1800, bookdecade1890, booksubjectzoology
