234 



COLLEGE ZOOLOGY 



tCJtf 



IcrJ 



dors.vess- 



we/tf- vess 

 -ne.ca 



Fig. 164. — Anatomy of Nereis, dors, vess, dor- 

 sal vessel; gl, oesophageal glands; int, intestine; 

 ne.co, nerve-cord; ncph, nephridia; ms, oesoph- 

 agus; palp, palp; para, parapodia; perisl, peri- 

 stome ; perist.tent, peristomial tentacle ; ph, 

 pharynx with its jaws ; praest, prostomium ; 

 tent, prostomial tentacles; vent. vess, ventral 

 vessels. (From Parker and Haswell.) . 



the sexes usually separ« 

 ate; and (2) the Oligo- 

 celeta, like the earth- 

 worm, with a lesser 

 number of sessile setas 

 projecting out from the 

 body-wall ; hermaphro- 

 ditic. 



Subclass 1. Polychceta 



Nereis. — Nereis (Fig. 

 163), the sand or clam 

 worm, is a common 

 annelid living in burrows 

 in the sand or mud of the 

 sea-shore at tide level. 

 The burrows are some- 

 times two feet deep and 

 are kept from collapsing 

 by a lining of mucus 

 which holds together the 

 grains of sand. By day 

 the sandworm rests in 

 its burrow, but at night 

 it extends its body in 

 search of food, or may 

 leave the burrow en- 

 tirely. 



A comparison of the 

 figures of Nereis (Figs. 

 163-165) with those of 

 the earthworm (Figs. 

 153-154) shows that 

 these two animals have 

 much in common, but 



