Title: Text book of zoology
Identifier: cu31924000397905 (find matches)
Year: 1896 (1890s)
Authors: Boas, J. E. V. (Johan Erik Vesti), 1855-1935; Boas, J. E. V. (Johan Erik Vesti), 1855-1935. Lehrbuch der Zoologie
Subjects: Zoology
Publisher: London, Sampson Low, Marston
Contributing Library: Cornell University Library
Digitizing Sponsor: MSN

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172 Annelida. â a few, or a single one. In some i'orms it has been found that tho individuals which produce buds develop no genitalia, whilst these are present in forma produced by budding, so that a regular alternation of genera- tions occurs; in other cases, however, both kinds of indi- viduals are sexual. Most Ohii^topods are marino, and for the iriost part crocj) about on, or burrow into, the soft bottom*; others (Oligochaitse) live in like maniicv in fresh- water or in damp earth; many forms, which usually live on the bottom, are yet able to swim by serpentine movotnents. A few are, however, truly pr 1 agic, and like other pelagic animals are transparent and provided with eyes, which for Annelids are of enormous size. A con- siderable number form tubes, consisting of foreign particles, mud, clay, sand, small stoiK^s, fragments of gastropod or lamellibranch shells, or rliizopod sIkOIs cemented together by the secretion of certain skin glands; tho separate particles are either irregularly united or neatly fitted into one another like a mosaic. The glands often secrete a chitinous tube, on which are plastered foreign bodies: in other forms tho case consists exclusively of the hardened secretion of the skin glands, and is then either chitinous or calcareous. The tube increases in sine .as the growth of the animal advances : lines of growth may be clearly discerned just as on a snail-shell. The tube is either fastened to some foreign object or lies free; rarely the animal carries it >tbout. Some Chaetopods, which are provided with strong pharyngeal teeth, lead a predatory life, others feed on algas; many are mud and earth- feeders, living on organic particles contained in mud, sand, or o;irth.
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Pig. 136. Chain-forming Chtetopod (Myrianida fasciata), with very long dorsal oirri.âAfter H. Milne Edwards. Order 1. Polychata. The prostomium and the peristomium are usually furnishu<l with appendages (cirri); eyes are frequently present. The cluetas ai'o borne upon true parapodia frequently provided with cirri; gills may * Some species can bore into rook, stone, or clay, but how they do it is not understood.

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