j„^, MARINE WORMS. PHYLUM ANNELIDA 



in most respects, lead a free and predacious existence. Of 

 these the genus Nereis, of which several species are found on our 

 coasts, is a good example ; Nereis cultrifera (Fig. 124) is common 

 under stones on the south coast of England, where it is known 

 as the red cat and is used as bait. The body of this worm is 

 about six inches in length, of a greenish colour, with red on the 

 Hmbs and where the dorsal blood vessel shows through, roughly 

 cylindrical, tapering towards the hinder end, and divided into 



Fig. 124. — Nereis cultrifera. — From Thomson. 

 a., Anus ; c, tentacular cirri ; e., eyes ; p., palp ; pe., peristomium ; t., tentacles. 



about eighty segments. Like the earthworm, it is covered with a 

 thin cuticle, but instead of having a small number of short chaetse 

 protruding directly from the body-wall, it has many longer 

 ones borne on movable lobes called parapodia, of v/hich a pair 

 is found on each somite. A parapodium (Fig. 125) is a fiat, hollow 

 vertical process of the body-wall, standing out at the side of 

 its segment. It is cleft into two principal lobes, a dorsal noto- 

 podium and a ventral neuropodium. Each of these is again 

 divided into smaller lobes and bears at its base a slender process 

 known as a cirrus. A stout, deeply embedded chseta or aciculum, 

 which does not project to the exterior, supports the notopodium 

 and another the neuropodium, and each of these bears a tuft 

 of other chaetae. In the sexually mature stage of the worm known 

 as Heteronereis these are oar-shaped and there are additional 

 complications in the parapodia. The front end of the body is 

 modified to form a definite head (Fig. 126). This consists of the 



