VERMES 



137 



SUBCLASS I. POLYCH^TA 



The Polychseta (Gr. 7roXv<;, many, and x aiT V, 

 bristle) are highly developed, marine Chaeto- 

 poda, very common in the sand and under stones 

 along the shore, and also found in dec]) water 

 ( Fig. 126). The body is generally greatly elon- 

 gated, sometimes consisting of hundreds of seg- 

 ments, and there is often a distinct, highly 

 differentiated head. This may bear two or more 

 eye and soft processes called palps or tentacles. 

 The mouth is on the ventral side of the head, 

 and opens into a pharynx, often protrusible and 

 provided with strong chitinous teeth. Almost Fig. 727. Pofynoe 



. setosissima. Dorsal 



every segment posterior to the head bears a pair asp ect, with pharynx 

 of lateral appendages, soft outgrowths from the protruded. (After 



1-1 11 11 j v Ti u 4-1 Quatrefages, from 



body-wall, called parapodia. I hey have the p a ,k,r and lias- 

 form of flattened, well's Text-book.) 



vertical plates, usu- 

 ally divided into two or more lobes 

 arranged in a dorsoventral series, 

 and bear the setae, which are usu- 

 ally very numerous and long. To 

 the dorsal edge of the parapodia 

 there are often attached long, slen- 

 der processes, sometimes shorter 

 and richly branched, the branchiae, 

 or gills, which are the chief organs 

 of respiration. Some curious- 

 looking Polychaeta are covered 

 with large overlapping scales, 

 which are really attached to the 

 parapodia and extend completely 

 over the dorsal surface (Fig. \2~). 

 In others, like the sea mouse 

 (Fig. 128), the bristles are very 

 long, delicate, hairlike, and iri- 



FlG. 128. Aphrodite aculeaia, the sea flpoppnf 

 mouse. (From Ludwig-Leunis' Synop- 

 sis der Thierkunde.) In this subclass the sexes are 



