276 



CCELHELMINTHES 



K 



Order I. Polychaetse. 



The Polychsctae owe their name to the fact that each group of bristles 

 contains many chaetae; but more important is that the bristles of each side 



are supported by a fleshy outgrowth of the 

 somite, the parapodium, in which two por- 

 tions corresponding to the bunches of 

 bristles dorsal, notopod'mm; ventral, neuro- 

 podium- may be recognized (fig. 254). 

 This is the first appearance of true appen- 

 dages, but they differ from those of Arthro- 

 poda in not being jointed to the body nor 

 jointed in themselves. On the dorsal sur- 

 face may occur diverse outgrowths, known, 

 according to position or function, as cirri, 

 elytra, gills, etc.; on the head, palpi and 

 tentacles. The cirri are long processes on the parapodia, and like palpi 

 are tactile (fig. 254). Elytra are thin lamelke which cover the back like 



shingles and thus protect the 

 body (fig. 262). 



Nearly all Polychaetes are dioe- 

 cious and undergo a more or less 

 pronounced metamorphosis; with 

 few exceptions (M anyimkia* from 

 the Schuylkill, Nereis* in California) 

 they are marine. They are usually 



FIG. 260. Head with pro- 

 truded pharynx of Nereis 

 versipedata (after Ehlers). c, 

 cirri, k, jaws; I, head with eyes; 

 p, palpi; t, tentacles. 



FIG. 261. 



FIG. 262. 



FIG. 261. Amphitrite oriiata* (from Verrill). 



FIG. 262. Head of Polynoe spinifera (after Ehlers). Back entirely covered with 

 elytra; cirri and parapodia projecting at the sides. 



divided according to their habits into fixed (Sedentaria) and free forms (Er- 

 rantia). The Sedentaria feed on vegetable matter, usually form leathery 



