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  .—Thucydides iv. 76; Diodorus xvi. 85-86; Plutarch, Alexander, ch. 9; Sulla, chs. 16-19; Appian, Mithradatica, chs. 42-45; W. M. Leake, Travels in Northern Greece (London, 1835), ii. 112-117, 192-201; B. V. Head, Historia Numorum (Oxford, 1887), p. 292; J. Kromayer, Antike Schlachtfelder in Griechenland (Berlin, 1903), pp. 127-195; G. Sotiriades in ''Athen. Mitteil.'' 1903, pp. 301 ff.; 1905, p. 120; 1906, p. 39 , 1908, p. 65.

  CHAETOGNATHA, the name given by R. Leuckhart to a small group of transparent and for the most part pelagic organisms, whose position in the animal kingdom is a very isolated one. Only three genera, Sagitta, Spadella and Krohnia, are recognised, and the number of species is small. Nevertheless these animals exist in extraordinary quantities, so that at certain seasons and under certain conditions the surface of the sea seems almost stiff with the incredible multitude of organisms which pervade it. Rough seas, &c., cause them to seek safety in dropping into deeper water. Deep-sea forms also occur, but in spite of this the group is essentially pelagic.

 CHAETOPODA (Gr. , hair,  , foot), a zoological class, including the majority of the (q.v.), and indeed, save for the  (q.v.), co-extensive with that group as usually accepted. They are divisible into the (q.v.) or Archiannelida, the Polychaeta containing the marine worms, the Oligochaeta or terrestrial and fresh-water annelids (see ), the Hirudinea or leeches (see ), and a small group of parasitic worms, the  (q.v.).

The distinctive characters of the class Chaetopoda as a whole are partly embodied in the name. They possess (save for certain Archiannelida, most Hirudinea, and other very rare exceptions) setae or chaetae implanted in epidermal pits. The setae are implanted metamerically in accordance with the metamerism of the body, which consists of a prostomium followed by a number of segments. The number of segments in an individual is frequently more or less definite. The anterior end of body always shows some “cephalization.” The internal organs are largely repeated metamerically, in correspondence with the external metamerism. Thus the body cavity is divided into a sequence of chambers by transverse septa; and even among the Hirudinea,