GENERAL SURVEY OF CH&TOPODA. 



205 



tubes, — limy, sandy, papery, or gelatinous. They are not nearly 

 related, but possess in common certain adaptive characters, such as the 

 aggregation of gills, cirri, tentacles, and sense organs to the anterior 

 exposed part of the body ; the reduction of the parapodia, often used 

 solely for clambering in the tube; the absence of "jaws," and the 

 habit of feeding on minute Algo? or other substances suspended in 

 water. Among these are included Serpula, which forms twisted limy 

 tubes outside shells and other marine objects ; the aberrant Sabellaria, 

 which often builds reefs of porous rock formed of the aggregated 

 sandy tubes ; the common Terebella or Lattice conchilega, with its tubes 



Fig. 90. — Free-living Polychsete {Nereis cultrifera). 



Note, as compared with A renicola., the absence of gills, and the 

 well-developed parapodia which are absent from the peris- 

 tomium (pe.), or first true segment. The prostomium bears 

 eyes(e.), and the small tentacles (t.) ; p., the large palps, c; 

 the four paired cirri borne by the peristomium ; a., the anus 

 with two long cirri. 



of glued sand particles ; and the strange Chtztoptents, found in deep 

 water, within its yellow parchment-like tube. 



III. EcbiuridEe. — In holes in the rocks on the warmer coasts of 

 Europe there lives a curious "worm" — Bonellia viridis , of a beautiful 

 green colour, with a globular body, and a long, grooved, anteriorly 

 forked, pre-oral protrusion. Such, at least, is the female ; but the male 

 is microscopic in size, lives in or on his mate, and is exceedingly 

 degenerate. His gut is without mouth and anus, the surface is covered 

 with cilia, and the body cavity almost obliterated. Related to Bonellia, 

 but of less anomalous shape, are a few other forms, like Thalassema and 

 Echiurus. 



In all, the body in the adult shows mere traces of segmentation ; 



