176 MARINE INVERTEBRATES 



jections on the swollen base, its terminal end smooth, with a circle of 

 round projections at the orifice ; color green, with a row of dark spots 

 down the center of the dorsal surface and a fainter line of spots on each 

 side at the base of the parapodia. Found on the New England coast. 



FAMILY NEBEIDJE 



GENUS Nereis 



Among the most common of the polychaete worms is the genus 

 Nereis, various species of which are found in all parts of the 

 world. They are abundant under stones, among seaweeds, and 

 living in burrows between tide-marks. They are active, fierce, 

 and voracious. Some attain a length of eighteen or more inches. 

 They are commonly known as "clam-worms/' 

 and are used by fishermen for bait. Nereis 

 has a distinct head, consisting of two parts. 

 One, the prostomium, bears on its upper side 

 four eyes and a pair of short, conical tentacles, 

 and on the lateral sides a second pair of pro- 

 cesses called palps. The palps are more con- 

 Head of Nereis pelagica. . r . 



spicuous than the tentacles, and consist ot 

 two parts, a large base and a small terminal point, the latter 

 capable of being withdrawn. The palps are sense-organs and 

 perhaps test the food. The second part of the head, or peristo- 

 mium, bears on the sides four pairs of long tentacles which are 

 used as feelers. The mouth is on the ventral side, and through it 

 Nereis throws out its phar} r nx, which contains a horny, notched 

 jaw. It seizes its prey with this jaw, which, with the pharynx, 

 is then withdrawn and tears the food apart, acting like a gizzard. 

 The body of Nereis is rounded above and nearly flat below. Each 

 of the segments has a pair of parapodia, bearing a bundle of bris- 

 tles and cirri. The last segment of the body is elongated, cylin- 

 drical, and without parapodia, but has on the end a pair of long 

 cirri, which give the appearance of a divided tail. Each segment 

 of the body, except the head- and tail-segments, contains a pair 

 of excretory tubes (nephridia), ganglia of nerves, and a portion of 

 the intestine and of the vascular system. There are circular 

 muscles by which the worm can diminish its diameter, longitu- 



