172 



Annelida. 



■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 p r 1 agi c, 

 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. 



Pig. 136. Chain-forming Chtetopod 

 {Myrianida fasciata), with very long dorsal 

 oirri. — After 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. 



